Diary Of An ADI

A Driving Instructor's Blog

An 'outdoor area' at a local pubMy local newspaper published an article about which pubs would be opening on 12 April. For anyone who doesn’t know, it’s those with outdoor drinking areas who are allowed to do so.

The photo above is the ‘outdoor’ drinking area of one of those being touted. Precisely how is it ‘outdoors’?

I’m now waiting for someone to convince me that if you stand in the middle of the Yorkshire Moors, you’re still ‘outdoors’ if someone builds four brick walls around you and plonks a roof on top (and, no doubt, installs heating and lighting).

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SpringWell, just over a year since the pandemic hit, and save for a few weeks at the end of last summer when it was relatively safe, on Monday I’ll be starting lessons again.

Unlike some complete prats out there, I realise that COVID a) actually exists, and b) is quite dangerous if you get it, so I will be taking it slowly and safely. Pupils will have to wear masks (unless exempt), they get gelled at the start of the lesson, the car gets wiped down in between (and fogged periodically), and I have a supply of lateral testing kits for myself – which I will use twice per week, and feed results back to the NHS as per the system. It may come as a surprise to the aforementioned prats, but as well as not wanting to catch COVID myself, not wanting to pass it on to anyone else is still pretty high on my list. I don’t want to be adding to the 127,000 who have already died from COVID – because I have morals.

I’ve had my first vaccination (the second is due in May), and I know that at least two of my pupils have either had it or have appointments booked. More importantly, both of my parents have now had both of their jabs – it has always been them I was most concerned about. Also, my pupils who are at school tell me they’re being tested regularly, which is good.

The fun has now started. One pupil has moved house since I last saw her, and instead of a 2 minute drive she’s now 40 minutes away and will be doing her test at a different centre to the one we had originally planned for. She doesn’t know that yet, and I know she’ll argue to use the original – but if people are doing one hour lessons and live in Hucknall, Colwick is a bit off the radar. Especially so at midday. I’ve been there, done that, and the T-shirt says clearly that it can take well over an hour just get to from Hucknall to Colwick and back again depending on the traffic and road closures.

Then there are the ‘can I have a lesson next week?’ texts. Except I vaguely remember (and I was right) that several of them work rotas with You-Know-Who on zero hours contracts, and ‘next week’ roughly translates to a free hour on Thursday at 5pm and one on Sunday at 9am, because they’re working (or at school) the rest of the time. And even that is subject to change if You-Know-Who calls them in.

Several other haven’t responded to my texts yet. Young people have their phone glued permanently to their hands the rest of the time, yet I can never figure out why some of them take a day or more to reply to any text. It’s like I’ll text them on a Monday with ‘are we still on for Saturday?’ By Thursday, no response. So I’ll text again, thinking about filling their slot with someone else who wants a lesson, and that will finally prompt them to tell me they still want it, like the first text never happened.

It’s just like old times already. And I haven’t started yet.

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The Chillmax AirI wrote this in the very hot summer of 2019, but each year around spring time adverts start appearing involving these ‘revolutionary no-install air conditioners’.

Be aware that these devices do not work to anything like the levels claimed. The original article follows.

Early in July 2019, I saw the Chillmax Air advertised on TV in one of those shouty ads. Then, the same evening, I was shopping in Asda and saw it on display. I am an idiot for things like this, and bought it on impulse so I could test whether it worked or not.

As a chemist, I know that in order to cool a large space effectively you’re going to need something with a big fan and a special refrigerant. In practical terms, that means a fairly bulky device with a motor-driven compressor, a closed radiator for the refrigerant to pass through, a fan to suck air in and blow it across the radiator, and a wide exhaust pipe through the wall or window to get rid of the ‘removed heat’. In some cases, you also need to collect or drain the condensed water that comes out of the air as it cools. A typical proper air conditioner for a small or medium-sized room will be about the size of bedside cabinet. The Chillmax Air is not much bigger than six CD cases glued into a cube.

If you’ve used a normal desk fan you will know that you only feel cooler if you’re sweating a bit. That’s because the fan evaporates your sweat as it pushes air over it, and that evaporation is accompanied by a small cooling effect – it’s called ‘evaporative cooling’. If you’re not sweating, you don’t feel the effect. Conversely, if the surrounding air is very humid, then no matter how powerful your fan is, you will feel little or no cooling because sweat can only evaporate if the air has capacity to hold additional moisture (I’ll explain that a bit more later, because it’s what determines whether the Chillmax is any good).

As an aside, many liquids exhibit the evaporative cooling effect. In the case of diethyl ether (the stuff they used to use as an anaesthetic), if you force it to evaporate very quickly you can even freeze water (if you do it properly). However, ether is both highly flammable and toxic, so apart from demonstrating it in the school lab (where I remember it from, partly due to the massive headache the fumes gave me), it doesn’t have much practical application these days. Early refrigerators used it, which was spectacularly dangerous.

The Chillmax Air uses the evaporative cooling effect of water, and this is much less than with ether – similar to sweat, in fact. The unit consists of a reservoir at the top, which you fill with normal tap water, and this drips down on to a radiator unit which has ten sideways-stacked fibre panels in it through which a fan blows air. The water evaporates from the fibre panels, and the evaporatively cooled air comes out through the front grille. According to the marketing spiel on the TV ads, you’d be forgiven for thinking you’re going to get frostbite if you sit too close. I knew this wasn’t going to happen, but I wanted to know just how effective the Chillmax was.

When I first set it up and turned it on, the first thing I noticed was that the fan is quite powerful, so you get a good flow of air directed at you – but note that that it’s only a 5″ computer fan, so it can’t beat a proper desk fan for air flow. The air did seem a little cooler compared with what my desk fan was blowing at me, but it also felt ‘softer’ – that’s very important, and I’ll explain later. But the big question was how much cooler was the exhaust air?

I fired up my trusty data logger and left it in front of my desk fan for 30 minutes for the control data. Then I moved it and suspended it in front of the Chillmax for the same period of time. This is what it recorded (the red line is where I moved it).

Chillmax - temperature log in hot and sticky conditionsThe ambient temperature where I ran the test was about 29ºC. The Chillmax brought this down by about 4ºC.

So, the Chillmax definitely cools the air that passes through it. Let’s work on the assumption that it would be able to get the same 4ºC drop no matter what the ambient temperature was. If your room is 38ºC, pulling it down to 34ºC still means it’s bloody hot. And also note that since the Chillmax is physically so small, the cooling is very localised – it won’t cool a room down, and you have to have it less than a metre from your face to feel anything.

Now, some people might be thinking that a 4ºC is better than nothing at all. And they’d be right if it was just a matter of temperature. But there’s more to it than that. I mentioned that the exhaust from the Chillmax felt ‘softer’. I knew what it was, but my data logger shows it in numbers.

These are is the data for relative humidity recorded at the same time as the temperature measurement, above (the red line is where I moved the logger). The humidity went up dramatically – a jump of about 30%RH.

Chillmax - RH log in hot and sticky conditionsAs I’ve already explained, the Chillmax works by evaporating water on fibrous panels by forcing air across them. That water has got to go somewhere, and in this case it comes out as vapour in the cooled air. In the right light, you can actually see it – it’s essentially fog. And just like when it’s foggy outside, and everywhere gets damp, this vapour can condense on surfaces. My data logger collected some and began to drip during the test, and I have since discovered that it also condenses on the front grille and can drip periodically, so you’d need to be careful what you had underneath it if you placed it on a shelf. The fan is quite powerful enough to project the drips forward slightly when they drop.

The ambient humidity in the room where I did the test was about 44%RH. The Chillmax sent that up to over 70%RH.

It’s this elevation of the humidity of the cooled air which really brings into question whether the Chillmax is worth the investment. You’re probably aware that you can have a hot summer day in the high 20s where it is pleasant and comfortable, but a cooler and overcast day might be horribly sticky – or muggy. That’s because of the humidity, or water vapour in the air.

The amount of water vapour that air can hold varies with the temperature. Once you reach the maximum, any extra vapour condenses out as a liquid – misted up windows, dampness, even drips and pools of moisture on window sills or under lamp posts. Cold air can only hold a small amount of moisture before condensation occurs, but hot air can carry much more (think ‘sauna’). Although ‘humidity’ technically refers to the amount of water in the air, the figure most people are referring to when they say it is relative humidity. This is the amount of moisture in the air expressed as a percentage of the maximum amount it could hold at that temperature, hence the units %RH. It’s a very complicated subject, but the important factor for us here is that when it is warm or hot, higher relative humidity is uncomfortable. Indeed, you may have seen weather forecasts where they give the actual temperature and the ‘feels like’ equivalent – that’s a reference to the ‘Heat Index’, which takes into account the effect of the %RH. Here’s a graphical chart for that.

Heat Index - graphical representationAs an example, if the air temperature is 30ºC and 50%RH, it will feel like 31ºC, but if the humidity goes up to 80%RH, then it will feel like 38ºC – even though the thermometer still tells you it’s 30ºC.

Another example. If the air temperature is 35ºC, at 50%RH it will feel like 41ºC, but send the humidity up to 80%RH and it’ll feel like 57ºC – even though the thermometer still reads 35ºC.

The calculation for this is complex (you should see how long my Excel formula for it is). It is non-linear, and the increase in ‘feels like’ is greater at higher temperatures. It also contains an element of opinion/perception, which is why there’s no point using numbers above about 60ºC. But the ‘Heat Index’ is what forecasters use. Incidentally, the official health designations for the colours are: yellow – caution; amber – extreme caution; orange – danger; and red – extreme danger. Vulnerable people need to take these into consideration before going out in hot weather.

However, this is where the problems come in for the Chillmax and similar devices. If it’s 35ºC and 40%RH, it’ll feel like 37ºC. Cool the air to 31ºC but send the humidity up to 80%RH, and it’ll feel like 41ºC. So it’s actually hotter in terms of comfort. Do the same comparison when the surrounding temperature is 38ºC, and the ‘feels like’ goes from 43ºC to over 50ºC!

At lower temperatures the Chillmax will produce a slight net cooling effect. But if the air temperature is above about 30ºC (and 50%RH) – which isn’t excessively hot or humid to start with – it’ll actually make you feel warmer. And if it is already humid outside, you’ll feel hotter still.

Proper air conditioners remove water from the air they cool. This removal of moisture is why the air from proper air conditioners feels crisp, as opposed to the ‘softness’ of moist air. The Chillmax does the opposite of normal A/Cs, and adds moisture.

Aesthetically speaking, the Chillmax is a cube – more or less – about 15cm along each side. There are two buttons on the top rear, one which changes the fan speed to one of three settings (or off), with a blue LED for each, and another button that turns the night light on or off. There’s a flap on the top front through which you add the water. The radiator system is a plastic-framed insert which you access by pulling the front grille out. It slots in and out easily. You can’t officially replace the fibre inserts in the radiator, but you can buy the whole radiator assembly from JML for £15. My only major gripe is the power cable. The jack plug that goes into the Chillmax is quite stubby and doesn’t go into the socket very far, so it is easy to dislodge it. However, the cable itself is quite long, and the  mains plug is a moulded UK type.

JML claims the Chillmax can run for up to 10 hours per fill, but this is likely on the lowest of the three fan speeds, since on top speed it runs out in less than three hours.  JML sells the humidification as a positive without relating it to the comfort relationship between temperature and %RH, but note what I said above. If you want to cool down in humid weather, it isn’t just the temperature that needs to come down.

Does it really work?

It does cool the air by a few degrees, so in that sense it works. However, it also sends the humidity up, and in most cases that actually makes you feel hotter and more uncomfortable. In that sense, it doesn’t work.

Will it cool more if I use ice water?

No. Evaporative coolers are not influenced significantly by the temperature of the water used in them. The temperature of the air that comes out depends on the temperature (and humidity) of the air going in, and the science of evaporation. Only this evaporation results in the cooling effect observed.

Will it cool more if I put the filter in the freezer?

It might – while you’re blowing air over ice. But once they defrost, which will happen in a few minutes in the temperatures you’ll likely be experiencing, then no. You’ll also have more condensate to deal with from the melted ice pouring out of the front grille.

You may see reviews on Amazon claiming that freezing the filters (or using ice cubes in the water tank) does give cooler air. Trust me – apart from what I just said about blowing air over ice, it doesn’t. Science is involved, and evaporative cooling doesn’t work like that.

Can I use it to cool my PC?

Someone found this article on the search term “jml chillmax air for pc cooling”. No. Blowing damp air into your PC would be dangerous, potentially expensive, and would only gain you 4ºC at best.

Can you get larger versions?

You can certainly get larger evaporative coolers, though not the Chillmax specifically. The working principle is that the larger the surface area of water, and the greater the airflow over that water, then the greater will be the possible drop in temperature at the front end. However, cooling effectiveness is influenced greatly by the RH of the air going in.

If the air is very dry, then a large evaporative cooler might be able to drop inlet air at 30ºC down by as much as 10ºC. However, if the inlet air is very humid, the temperature drop could be as little as 1ºC. In the UK, the realistic temperature drop you could expect on a non-humid day for a large cooler would be around 5-6ºC, but on a sticky day you’d only get about a 3ºC drop.

Suppliers of these devices say that they need good ventilation or extraction, and I would imagine that’s so the humid air can escape. If you’re evaporating more water to get better cooling on larger devices, you’re also producing a lot more water vapour. Be careful if you read any of the reviews – people may have noticed cooling in already cooler conditions, but trust me – if it’s very warm and humid, you will not notice any effect.

People say it works

Be careful when you read those one-line reviews. If you test it when it’s only 20ºC outside – as many of these people have – then yes, it blows noticeably cooler air at you. But science is involved, and at temperatures above about 28-30ºC you’ll actually feel hotter. The fact that it increases humidity is the key factor. Remember that the reason you even found this article was probably because it’s over 30ºC outside – the more above that it is, then the more hits I get.

So, does the Chillmax work?

It cools the inlet air by several degrees. But it sends the humidity of that air up considerably, and this cancels out the benefits of the cooling effect when it is very hot. The ‘Heat Index’ is the key detail, as explained above.

Only the air being directed at you is cooler. Once that slightly cooler air has passed through warmer air, it’ll be close to ambient again. The device cannot cool down a room. It’s far too small for that.

Humidity can carry much further, though. So in a small room, you could easily increase the ‘ambient’ RH without any cooling at all, and that will make it feel even hotter. If it is already hot, the amount of water vapour the air can hold before reaching 100% RH will be substantial. The increased humidity of the outlet air does produce localised condensation, so you have to be careful to keep it away from electrical sockets where it might drip on them. The unit also contains a significant volume of water when full, so you don’t want to knock it over.


It’s that time of the year, people! In the UK, at any rate. Spring starts this weekend, and my tree is already putting out catkins. Time to start feeding.

Our Silver Birch in June 2017I originally wrote this article back in 2014. At that time, our tree began to produce a lot of yellow leaves in mid-June, and after a lot of research I managed to figure out the cause and remedy, which was what this article was originally about.

However, 2018 was the hottest year on record. The heat lasted for months, and it introduced another problem (which may well have been a contributing factor back in 2014 without me realising it) that affected pretty much every tree in the country. Heat stress.

The article becomes popular each year, but things kicked off much earlier in 2019, and I suspect that this was down to a combination of the after-effects of the 2018 drought and a relatively dry and mild Winter. As a result, people began to see problems much earlier because their trees were already on the back foot.

We also had a lot of green fly in 2019, possibly caused by the mild winter. In Spring and early Summer they were merrily chowing down on the new leaves on my tree. I bought some Ladybird larvae and released them into the canopy, and they seemed to do the trick.

But to summarise the subject of premature yellowing and leaf drop in Silver Birches over the last few years, it can occur for the following reasons:

  • nutrient deficiency
  • iron deficiency
  • lack of water and heat stress
  • manganese deficiency

It’s easy to get all of them at once. And do not under-estimate the importance of water – even if you think the soil is wet enough, there’s a good chance that deep down the tree doesn’t see it the same way.

When I first experienced yellowing back in 2014, I was worried. I thought my tree was dying. Googling for an answer was pretty much useless, because most of the technical advice is American and focuses on the Bronze Birch Borer (a beetle that feeds on white birches), which isn’t known outside of  North America, or the drawbacks of trying to grow trees in deserts or swamps (neither of which Birches are particularly fond of). And that was only from the experts. These days, if you don’t know the answer to something, standard procedure is to guess the most outlandish explanation possible, spread it around, then defend it vigorously when people laugh at you. The average tree-growing American was quite prepared to blame their problems on the Democrats, the Republicans, or an alien conspiracy!

So back in Blighty, the Birch Borer was definitely out. And although the British never shut up about the bloody weather, we were growing ours in normally-drained British garden soil, where it had been happily and vigorously growing for the previous 15 years.

I concluded that yellowing/leaf drop can be caused by nutrient and iron deficiencies in the soil. I subsequently discovered, especially in 2018, that lack of moisture and prolonged high air temperatures can lead to heat stress, which birches are highly susceptible to (I wrote a separate article about it in August 2018).

None of these problems are confined to Silver Birches. All trees and plants can be affected by nutrient deficiencies or heat stress. And you simply have to deal with the problem using the appropriate, easily purchased treatments. All of the suggested treatments mentioned in this article are shown in the box below.

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My original 2014 problem was characterised by bright, canary yellow leaves – just like in the Autumn. Not as widespread throughout the canopy – just a few clusters – but still enough for the tree to start shedding them. I can’t remember where I found it, but somewhere in amongst the interminable forum pages and obscure “ask the expert” sites rattling on about the bloody Birch Borer I came across a single one-line comment that made absolute sense and led me down the nutrient deficiency path.

Birches favour a slightly acidic soil – they are sometimes referred to as ericaceous (lime-hating). Therefore, you can replace essential nutrients and fix any issued with nitrogen deficiency using ericaceous fertiliser. Initially, I used the Miracle-Gro solid version, which is available from garden centres and online (including eBay and Amazon). It’s not expensive, and you often get multi-pack deals. You can also get liquid varieties, such as the one manufactured by Doff, which I switched to in 2018 because of my new irrigator toy. And you can also buy  slow-release granules, which work for up to three months, and which are great for treating small areas (I use them in my containers of Blueberries, which are also ericaceous).

Normal fertiliser is no good for birches – it has to be the ericaceous stuff, so don’t waste your time using whatever it is you have in the garage or shed if it doesn’t say it is specifically for ericaceous plants. You just dissolve or mix it with water as per the pack instructions, and spread it around the tree. The slow-release granules are sprinkled on the ground and initially watered in (I just wish they’d make the damned things in camouflage green, instead of the “hey, look at me all over the lawn” multicoloured mix they actually are). Then, when it rains – or in subsequent watering sessions – more of it dissolves and the feeding continues. In all honesty, you cannot rely just on the slow-release type if you have an immediate yellowing problem. You’ve got to get a lot of food down to the roots fast.

Leaves suffering from chlorosisIron deficiency causes yellowed leaves to look like those in the images here. It’s known as chlorosis.

Most plants have leaves which are usually green because they contain chlorophyll – and chlorophyll is green. Simplifying the subject, chlorophyll is what allows plants to convert light energy into sugars that they can use as food through the process called photosynthesis. Plants use iron to produce chlorophyll, so if there isn’t enough iron in the soil the tree can’t make enough chlorophyll, and you get yellowed leaves. The tree compensates for being hungry (if it hasn’t got chlorophyll it can’t make food for energy) by going into shutdown and shedding those leaves.

Chlorosis is resolved using sequestered (or chelated) iron, such as Maxicrop. It’s a seaweed extract, so perfectly natural, and it comes as a liquid. You can mix it in with your fertiliser and water it in at the same time. I buy it in commercial 10L containers, which is more cost-effective than buying it in 1L bottles. It stains like hell, so be careful not to drop any on pathways and decking (it’s OK when it’s diluted, though).

Close-up of leaves suffering from chlorosisAnother symptom of soil nutrient deficiency is that new leaves may be small and misshapen, instead of the classic Birch leaf shape. Some of ours were like that in that first season, though I didn’t take any photos of them.

A single application of fertiliser in that first year stopped the leaf drop almost immediately once the already-yellow leaves had fallen. The tree even threw out some large catkins, which had been absent up until then, so it obviously enjoyed what I’d fed it. Since 2014, I begin feeding every few weeks from the beginning of March with both fertiliser and iron, and had no significant issues after than until 2018.

Close-up of our tree's leaves in June 2017To get iron into the soil, you can also water-in iron (ferrous) sulphate periodically. It also has the advantage of gradually  acidifying the soil, which might be useful if yours is a bit too alkaline. If your soil pH is above about 6.5, then iron already in the soil is not available to the plants growing in it, and this can cause chlorosis problems. Iron sulphate is also a superb moss killer and grass greener – my lawn loves it.

The brand I recommend is by TradeFarm NI – is a free flowing and stable powder as long as it is kept dry (I think it is either the monohydrate or dihydrate salt). Be wary buying cheaper brands which are ‘damp’ (heptahydrate) crystals, because they go off very quickly and turn brown (which is the ferric salt, and this could be corrosive to plants). I recommend TradeFarm NI from experience, having been down the route of the other kind.

Why does nutrient deficiency occur? Well, bear in mind that when trees and plants die back in winter in the wild, the leaves they shed decompose and return nutrients to the soil as they do so. In urban gardens leaves are usually swept up and taken to the tip to keep the garden looking tidy. That means the soil becomes depleted of those nutrients over time and you get problems like this. I used to think that all you did was plant a tree and watch it grow, but I know now that you have to look after them like any other plant in your garden.

You have to keep these treatments going at least once a month between March and September, and you have to follow the same routine each year, or at least over alternate years. If you don’t, the problem will just come back at some point.

Now we come to the extremely hot summer of 2018. Around the end of June that year, I once again noticed a few sprays of yellow appearing. I briefly wondered what was going on, but I guessed right away it might be linked to the prolonged high temperatures and low rainfall we’d experienced up until then. After Googling it I concluded my tree was, indeed, suffering from heat stress. The solution to this is to get water down to the roots – it’s called deep watering – but that’s easier said than done.

One way of doing it is to use deep watering spikes. These are tapered tubes that are hammered into the ground around the tree, and into which water is fed slowly so that it gets to the roots deep down. I didn’t have time for that (with the ground as dry as it was, it’d have been like trying to hammer a nail into plate steel), so I went for the longer-term sprinkler method. Every night, I set the sprinkler going and watered for a couple of hours in each of several zones to ensure even saturation. We didn’t have any hosepipe restrictions, and I wouldn’t have continued if we had. This allowed water to seep down deep into the hard soil, and it fixed the problem in less than a week. It also turned a completely brown lawn into a lush green carpet.

With hindsight, all trees in 2018 had much thinner canopies than usual. The leaves on my own trees were smaller than they were in previous years, but about a week after starting deep watering the birch produced some new shoots and the leaves that appeared were much larger. And some very fat catkins also appeared. And with further hindsight, I am convinced that lack of moisture deep down may well have also contributed somewhat to my original problem.

As a result of the heat stress problem, and still needing to keep the other treatments going, I have now invested in a combined watering/fertilising system, which I have written about separately. I can highly recommend that device – the Access Irrigation Static Dilutor.

Can you rescue leaves which have turned yellow?

No, probably not. I suppose that chlorosis could be reversed if you caught it early enough, but if the leaf is dead and the tree has triggered its shedding mechanism, you’re going to lose them.

The important thing is that by feeding and watering the tree you can stop any further yellowing – and believe me, the first time you do it the effects will be quite noticeable within a short time.

Do you have to keep treating the trees?

Yes. If you don’t, the problem just comes back once the tree has used up what you’ve fed it, especially if you bin the leaves again the following autumn. Huge trees will suck up all the nutrients and water, and if you’re raking up and binning the leaves each year (or if the soil is dry and there are no prolonged periods of rain) nothing gets returned to the soil.

How often should you feed?

Treat them once or twice a month from March until September. And water regularly.

Can heat and drought cause them to lose leaves?

Yes. If they are stressed you may get them dropping leaves. In extreme cases the leaves can go brown and the tree can even die. It’s a good idea to water them deeply during hot, dry periods. Once or twice a week should be enough, though more frequently won’t hurt if the dry period is prolonged.

Remember that after a period of drought (or prolonged dry weather) it needs an extended period of rain to wet the soil again, especially deep down. A few heavy downpours won’t do it, and you will still need to help things along.

Will a Birch recover from drought?

It depends on whether the drought killed it or not. A reader wrote to me in 2018, mentioning that his tree had lost its leaves, and I advised that the only thing he could do right then was to feed and water – and hope for the best. He wrote to me in 2019 to tell me the tree had started to rock in the wind, and that a tree surgeon had subsequently declared it dead, and had had to remove it. Apparently, the roots were rotten.

There’s no way of knowing if it was just the drought that did the damage. The tree may have been weakened by not feeding and watering over previous years, and the drought was just the final nail in the coffin. But the 2018 heatwave certainly caused problems.

Is there any other way to deal with the problem?

You have to get nutrients and iron back into the soil. And you need water in order for the roots to be able to access those nutrients. Yes, you could use your own mulch or bought compost, but obviously this is not so attractive in a normal garden (removing it is what got you here in the first place). It would also take longer to have an effect. But it would still work, given time.

When do Birch trees normally start to shed their leaves?

In the Autumn! In the UK this is from around September-October, and the onset varies up and down the country. It often seems triggered by a noticeable drop in night time temperatures. The leaves will begin to fall from that point – very lightly at first, then increasing as the yellowing spreads.

Why do birch trees drop leaves so early?

They don’t. They drop them in Autumn, like all other trees which shed their leaves each year. If yours is turning early, you may have a problem.

How do you apply these treatments?

You make up the required solution as directed on the pack, then water it into the area specified. I use a combined watering/fertilising system, which I have written about separately. However, you can use a watering can and hosepipe/sprinkler as necessary. Note that if the ground is dry, a watering can won’t get the nutrients down to the roots, so a heavy watering is essential.

Why are fallen leaves sticky?

You’ve probably got greenfly! Specifically, the birch aphid, Euceraphis betulae. They feed on the European Birch, Betula pendula, and they increase in number during warm and dry weather – which is what we have right now (and did have for most of the winter). Aphids secrete honeydew as they feed, and that’s the sticky stuff you’re seeing. Apparently, you can get different species of greenfly that feed on specific trees.

You can kill them with a soap/water mixture, though no one has ever been able to tell me precisely how you apply that to a 20 metre high tree. And the same goes for any chemical method relying on direct contact. An alternative solution is to introduce predatory insects – something that eats aphids. The best one is the Ladybird larva, and you can buy them online. There are other predatory insects you can buy, too.

My tree is losing branches and twigs

If the tree is weak then it is understandable that twigs and small branches might fall off. Once they’re stronger this will stop. In any case, if it is windy, a few dead twigs are bound to fall off. It’s just nature – and birches also have a fungus which can cause small twigs to die and fall.

Early in the year, another likely problem is crows (the winged variety). From March (February in 2019) they will be nest-building, and they are very, very selective in their choice of twigs for the purpose. We get them nesting near us, and they will tear off a hundred twigs and drop them until they get the one they want. It’s nature, so we don’t worry.

Why do Silver Birches drop so many twigs?

As I said above, crows (and similar birds). As of February/March they are usually actively nest building.

When do birches start to show leaves?

In spring, obviously, but the precise date varies depending on both the tree and the weather. In 2019, they were about a month earlier than 2018 in the UK. Mine is usually showing leaves sometime during April each year.

I’ve got catkins but no leaves

Someone found the site in April 2018 with that query. You’ll probably find that in a couple of weeks you’ll have lots of leaves. As I have said in this article, I start feeding mine from March onwards. Leaves start sprouting a week or two earlier than my neighbours’ trees, and the foliage on mine is usually much denser. The catkins often come before the leaves.

Are the leaves changing early this year?

This was a generic search term used to find the blog in mid-July 2017. The short answer is no, they are not – not in July in the UK, anyway. They change towards the end of September in the UK.

Do Weeping Silver Birches lose their leaves in Autumn?


When do Silver Birch leaves go all brown?

They don’t. The leaves should go yellow and fall off in the autumn.

I had quite a few visitors from this search term in 2018, and when I looked it up it seems that extreme cases of chlorosis and heat stress can result in leaves turning brown (see this supplementary article). It could also be a disease or infestation which you could treat, but the tree itself might also be dead – especially if it has been having any of the problems I mentioned above over previous years. Best to call in the experts.

Does this advice only apply to Silver Birch trees?

No. Chlorosis can affect many plants, and lack of nutrients is a universal issue. You might need a different fertiliser to address any nutrient problem, but iron will likely fix chlorosis. Lack of water can kill virtually any plant.


The COVID penaltyWell, I had my first jab on Thursday. I got myself officially registered as a carer (I don’t understand why I already wasn’t), and booked immediately.

It didn’t hurt, though I have to say it was the most uncomfortable jab I can remember having. Mind you, that might have been just a throw of the dice as to where the needle went in. No side-effects until about 15 hours later, when I ached a bit for about six hours. After that, no signs at all – not even an aching arm.

For any of the nutjobs out there, I don’t send the TV funny when I walk past it, nor do I attempt to phone home when I’m near a Wi-Fi hub. And as far as I can ascertain, my mind is not being controlled remotely by anyone.

The only minor downside (to me, at any rate) is that I had the AstraZeneca vaccine. If allowed to choose, I’d have preferred the Pfizer/BioNTech one. Why? Because of the nutjobs.

You see, no vaccine is ever 100% effective. That means that every time you go out, if you are ‘challenged’ by someone carrying the virus, there’s a 20% chance you’ll catch it. It’s not quite that simple, but it’ll do for this discussion. The problem then is the number of times you are ‘challenged’ – and the more non-vaccinated people there are, the greater the number of challenges. It’s like saving a penalty in football – if you only get called on to try once, you might save it. But if you have to save 100 penalties, the likelihood of letting one in increases. And the nutjobs out there are the penalty-takers, so the more of them there are, the greater your chance of letting one in.

Having said that, there is mounting evidence that having been vaccinated also reduces the chances of you becoming seriously ill if you do catch COVID, so you could say it’s like having two goalkeepers trying to save the penalty.

The AstraZeneca jab is less effective than the Pfizer one according to the clinical trials, hence my preference.

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DVSA LogoA DVSA alert clarifies once and for all that theory test certificates will not be extended for road safety reasons.

The government has further considered the impact of the coronavirus pandemic on the validity period of theory test certificates.

After careful consideration and in response to a recent petition the government has decided not to extend theory test certificates for road safety reasons.

This is the government’s decision – not DVSA – so I’d advise a lot of people to think of that before venting on social media.


Smearing windscreen in rainPlease note that screen wash – even at its most concentrated – has a very low alcohol content and cannot be used as a hand sanitizer.

I’ve mentioned this in the smearing windscreens article, but we’re approaching that time of year where it gets wet and cold, and a lot of crap gets thrown on to your glass and builds up into a nasty film that doesn’t easily wash off.

It amazes me that some people – even driving instructors – only put water in their wash bottles (if they have anything in at all). And hearing them try to justify it just cracks me up.

Water on its own does not have sufficient wetting properties to attack oil, wax, and grease, and even proper washer fluid can have problems – it’s why  you get that mosaic pattern left behind when you wipe in the wet. You need a good detergent to clean off oily deposits, and a small amount of alcohol to assist with wetting. Alcohol also functions as an antifreeze, so whereas using just water means you’re going to get a popsicle with the first frosts, a proper washer fluid will protect you to well below freezing as long as you have it at the right concentration.

You can buy two types in the stores – concentrated, or ready-to-use. In most cases, the ‘concentrated’ stuff will act as an antifreeze when used neat down to about -9°C for the most expensive brands, or -6°C for the routine stuff (some brands claim -20°C). The freezing temperature is dependent on the amount of alcohol in it, and it’s obviously cheaper to make with less alcohol. For most of the year, you might use this concentrated stuff diluted between about 1:5 to 1:10 with water, but the colder it gets the more concentrated liquid you need to avoid freeze ups.

The ready-to-use stuff is used neat, but you need to be aware of what temperature it will go down to before it freezes. Some brands are good to -4°C, and with the weather in early 2021 in the UK that would almost certainly freeze up on you. If you’re somewhere where it gets really cold, it would be no good at all. They also sell ‘summer screen wash’, which contains little or no alcohol.

The price of typical concentrated screen wash varies from about £5 per 5L in summer, to about £8 in winter (when you need it the most). The ready-to-use stuff is similarly priced, even though it is more dilute. In a bad winter, with lots of rain and slush, I can easily get through 5L of washer fluid each week. I use less in summer, but over a year it can mount up. Not to a huge amount, but it’s still an overhead.

If you’re going to buy it, my advice is to stock up in summer when the prices are lower, and only get the concentrate so you’re not paying someone to dilute it for you. You often get BOGOF offers in summer.

However, it can be cheaper to make your own (it definitely was when I first published this). I got the idea when I had a freeze up one time (I was late switching to my winter mix), and solved the immediate problem by nipping into a hardware store and buying a bottle of methylated spirits. Adding that to my wash bottle depressed the freezing point and I was running again within 30 minutes. There was also the fact that my garage was overflowing with the stuff I’d stocked up on.

When I started making my own concentrate I was using bio-ethanol, which is a clean-burning fuel for home heaters. However, most of this comes from the EU (even the UK-branded stuff), and as a result of the insanity of Brexit the price has gone up to cover import duties.  You can still get it for as little as £3.40 per litre, but the number of suppliers has dropped and the price of UK supplies has gone up. Alternatively, denatured ethanol supplied as a cleaning agent can also be used, and you can get it for as little as £3.80 a litre.

Washer fluid needs to do two things:

  • clean
  • not freeze when it gets cold

It’s basically just a mixture of alcohol and water with a bit of detergent.

The alcohol – usually as ethanol – functions as an antifreeze and a wetting agent. The whole subject of freezing point depression in alcohol/water mixtures is a huge topic in physical chemistry, but the bottom line is that pure water freezes at 0°C, whereas adding alcohol lowers (depresses) the freezing point. A 10% ethanol/water mixture freezes at -4°C, a 20% mixture freezes at -9°C, and a 30% mixture freezes at -15°C. A typical commercial concentrate might claim that it freezes at -6°C when used neat, and this means it must contain 15% alcohol.

Alcohol is the most expensive ingredient in screen wash, and 5L of a 15% solution will have 750mls of ethanol in it. The cost of alcohol varies depending on current circumstances, but it’s cheaper the more you buy.

Whatever detergent you use has to be relatively non-foaming – you don’t want bubbles blowing down the street when you use it – and it has to be the kind that is actually going to attack the crud that gets on your windscreen. This is another big chemistry subject, but to cut a long story short, Traffic Film Remover (TFR) is ideal. TFR gets anything off your car – tar, oil, mud, insects, bird crap, dead squirrels, that sort of thing. I get mine from JennyChem, who also supply a range of car products the car washes use. You only need to use it at a concentration of between 1% and 2%, so one 5L container goes a long way, and will make up to 70 batches of screen wash.

Finally, there’s the water. It depends on how anally retentive you are on the subject (for me – very). Tap water is what most people would use, but – and depending on where you live – this can leave mineral deposits on the glass as streaks if you’re in a medium or hard water area. You can buy deionised water, which has the minerals removed, but it costs money – unless you have access to a supply of it, which you might. Alternatively, rain water (boiled and filtered), or – and what I use – the condensate from a dehumidifier, provides soft water which leaves no streaks.

Making your concentrate is easy. Get an empty 5L container (the kind screen wash usually comes in), add 750mls ethanol, 75-100mls TFR, and top up to 5L with water. Mix well by shaking the container. Used neat, this will protect down to about -6°C, but in summer you can dilute it as low as 1 part to 5 parts of water (1:5).

Personally, I make my screen wash fluid ready-to-use as I need it (I make three or four batches at a time and just keep them on hand, making more as required). In summer, I just make it with less alcohol – 100mls or so – and use more water.

For comparison, if I bought a 5L bottle of screen wash concentrate right now (February 2021) which was good down to -6°C when used neat, it would cost somewhere between £8 and £11. A 5L batch of my own stuff good down to the same temperature would cost £3.12.

A 5L bottle of ready-to-use summer mix would cost £6 bought online. My own summer mix costs £1.22 (though it could be as little as £0.27 without any alcohol in it).

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What if the temperature goes below -6°C?

You just need a higher alcohol content. Protection to -6°C requires about 15% alcohol, but 20% will give -9°C, and 25% will give about -12°C. However, bear in mind the flash point of alcohol solutions. My advice is  not to exceed 25% alcohol by volume.

How can I prepare for cold temperatures?

Use common sense. In summer, a high alcohol content of the screen wash in your car is just a waste of money. Dilute the concentrate about 1:5 with water (it would freeze at just below -0°C). When it gets colder, and sub-zero temperatures are likely, a 1:1 dilution will cover you to about -2°C, a 2:1 dilution to about -4°C, and a 3:1 dilution to about -5°C. As we have said, the concentrate used neat would be good as low as -6°C.

Can I make it with more alcohol in it?

Yes, but be careful. Ethanol is flammable, even in water mixtures. On its own it has a flash point of 14°C (that means that at that temperature and above, a combustible vapour exists that can easily be ignited). A 10% solution in water has a flash point of 49°C, which is much safer. A 20% solution has a flash point of 36°C, which is still safe unless you store it in a very hot place. A 30% solution has a flash point of 29°C, and this is quite likely to be encountered in hot weather. My advice is not to exceed about 25% of ethanol.

A concentrate made using 1L (20%) of ethanol instead of 750mls will be good down to  -9°C. A 25% mixture will cover you down to -12°C. Any more than that, and be careful. Don’t store a strong winter mix in your car during the summer. And definitely don’t carry any neat ethanol during the summer months.

Can I use isopropanol instead?

Also known a Propan-2-ol, 2-Propanol, and Isopropyl Alcohol (IPA).

Short answer, yes – but only if the sub-zero temperatures are a few degrees below zero. IPA has a lower flashpoint than ethanol, and  anything above 20% is risky. IPA also has a distinctive smell.

Can I use Methanol?

I’m just going to say no. It’s poisonous, and could be dangerous, so for that reason you should not use it.

Can I use methylated spirits?

Usually, this contains methanol as the denaturant – though sometimes other chemicals are used. It also has a strong smell. Apart from the time I used it in an emergency, I would advise against it. However, if you can find ‘denatured ethanol’ or ‘denatured ethyl alcohol’, and can be sure it doesn’t have methanol in it, that would be fine. It’s usually (not always) the blue stuff that contains methanol.

It seems complicated making your own

That’s why there is a market for ready-to-use screen wash. It’s up to you.

I just use water as a screenwash

Water on its own is no good. If the temperature falls, it will freeze. Even if it doesn’t freeze in your main washer bottle, it will in the pipes and at the nozzles, and freezing water is quite capable of splitting pipes or closed containers. Water alone doesn’t clean many things off the glass – it won’t touch oil, grease, or squashed insects, and it will struggle with tree sap.

If you do get a freeze up, trying to use the pump might cause it to burn out. Although I haven’t come across the problem recently, even if it doesn’t split your feed pipes it can cause them to become detached inside the car (it was a regular occurrence (well, it happened twice) on a Citroen Xantia I used to have many years ago).

Remember that if you are driving without the ability to keep your windscreen clear, you are committing an offence. The Road Vehicles (Construction and Use) Regulations 1986 says:

Every wiper and washer fitted in accordance with this regulation shall at all times while a vehicle is being used on a road be maintained in efficient working order and be properly adjusted.

Arguably, you are not complying with this if you just use water. If it freezes (or the bottle is empty) and you drive, you’re definitely not complying with it. It is shocking that some ADIs are apparently doing this.

Can you dilute ready to use screenwash?

Of course you can. It’s not a magic potion – just a mixture of water, alcohol, and detergent. I wouldn’t dilute the ready-to-use stuff more than about 50:50 with water, though, because the detergent probably wouldn’t do its job properly. And if it has a stated freezing point, just remember that diluting it means it will freeze at a higher temperature, and that could catch you out in winter.


DVSA LogoAn email alert from DVSA came through today. In it, they outline measures for handling the increased demand for tests.

I wrote recently that only specific key workers can still get tests. This email doesn’t make it clear in regards the time frames based on the key worker situation, but I am assuming that it means once we can all start working again. To that end, they are running a recruitment campaign for driving examiners.

So if the last 12 months has put you off being self-employed, that might be something to consider.

One key point in the email is that DVSA says:

How to reduce waiting times

We also need support from you, your pupils and our examiners to help us reduce driving test waiting times…

It is vital that your pupils are test-ready when rearranging their tests, as tests could be at short notice.

I know it will fall on a lot of deaf ears, but since most pupils – even those who were test ready – haven’t driven since March 2020, there’s just an incey-wincey chance that booking a test for them as soon as you can get one is going to backfire, because they won’t still be test ready.

I guess the upside to that (for some people) will be that if their little darlings fail, they can then blame DVSA about the length of time for the next test, the reason they failed, and so on.

Plus ça change…


Cooked riceAt the moment, my newsfeed is filled with stories about ‘the best rice cooker’ – probably as a result of my browsing history, I admit.

They’re all-singing, all-dancing electric things that do far more than you actually need. Now, I know that a lot of Asian people swear by electric rice cookers, but they tend to be fairly simple machines. In the West, we try to incorporate functions that are useless – like being able to play Netflix movies while you’re controlling the central heating. Stuff like that.

I can tell you now as an absolute fact, the only rice cooker you will ever need – assuming you have a microwave oven – is the Sistema Rice Cooker. All you do is put one measure of rice in the pot, add one and three quarters (or two) measures of water, and a little salt, and microwave on high for 9-10 minutes. Give it a stir, let it stand for another 5 minutes, and you have perfect rice. Period.

And it’s about a tenth of the price of the fancy ones. Sistema make some good food storage containers, too.

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£20 notesPeople keep asking this. I’ve had two emails this week: how much do you earn as an instructor? When it is asked online, almost every time some dipstick somewhere tries to answer it by doing it all wrong, or by making it too complicated.

If you were in a salaried position where the stated wage was £30,000 per year, that would be before tax and National Insurance. Any comparison for being self-employed also has to be before tax and NI. That’s because tax and NI are different for everyone (single, married, disabled, and God knows what other things). You need to keep these out of it in order to compare with self-employed income.

In a salaried position, you get the stated wage no matter what you do. If it says you get £30,000 a year, then you get £30,000 a year – before tax and NI. If you change to another salaried job, if the stated wage of the new job is £32,000, then you will be earning £2,000 more – before tax and NI.

To compare a self-employed job, you need to get an equivalent figure before tax and NI.

Being self-employed is different to being salaried, because you are not guaranteed an income. It depends on how much work you do, and in the case of a driving instructor, that work could be anything from 0 hours up to 50+ hours in any given week. It would be utterly stupid to budget based on doing 50 hours every week, and what you need is the average for an entire year. Since you are trying to predict a career change, you need to assume a sensible average figure and not just a big number you like the sound of – and which you would not be able to achieve reliably, if at all.

If being an ADI is going to be your main source of income, you need to be thinking of around 30 hours as a safe and sensible average figure once you are established. In reality, work will fluctuate, and if you end up averaging 35 or 40 hours, that’s great. But don’t get carried away, because something might happen which brings the average down to 25 hours or even less, and it is much harder to sustain a higher average than it is a lower one. If you underestimate, anything more is a bonus. But if you overestimate, not achieving it could be disastrous if you’ve bet your house (or mortgage repayments) on it.

Then there is your hourly lesson rate. Not everyone can charge £40 an hour. Some ADIs live in areas where £25 might be at the top end of what people will pay. Find out what your area’s average is and use that. In Nottingham, for example, £30 an hour is a sensible and realistic hourly rate right now (elsewhere on the blog I have referred to figures of £25 and £27 from when those were typical rates).

Finally, how many weeks will you work? Let’s assume – sensible assumptions are important when you’re self-employed – that you work 48 weeks of the year.

The maths is now quite simple. 30 hours a week times by £30 an hour times by 48 weeks means you will be taking £43,200 from your pupils each year. That’s your turnover (total income).

But you also have business costs, or expenses. You have to pay for your car, fuel, insurance, and so on, and you use your turnover to pay for these. No matter what you see the feral monkeys on social media claiming, they do not run a car ‘for nothing’. One way or another there is a weekly business cost associated with even the most dilapidated and ancient jalopy you could find. The vast, vast majority of instructors will have weekly vehicle costs of at least £100 (for the whole 52 weeks of the year). Fuel is also around £100 for a 30 hour week (for the 48 weeks you work).

Combining these, your car costs will amount to £100 times by 52 weeks, totalling £5,200. Fuel usage is £100 times by 48 weeks, which totals £4,800. Together, that’s £10,000 of expenses.

Therefore, your actual income – your wage before tax and NI – based on an average of 30 hours per week at £30 per hour is £43,200 minus £10,000, which equals £33,200.

Before you drool all over your keyboard, it’s worth considering a few realistic and quite possible variations in this calculation. Firstly, what if you only average 25 hours a week instead of 30? In that case, your annual wage would drop to around £26,500.

Secondly, what if you do 30 hours, but can only charge £27? In this case, your wage would be around £29,000.

Thirdly, what if you average 25 hours and can only charge £27? Now, your wage would be around £23,000.

And finally, what if you don’t get anywhere near an average of 25 hours in your first year? Will it be enough to pay your bills?

It’s easy to put all this into a simple spreadsheet to compare the different scenarios and variables. But one look at what’s happened in the last year should be enough to hammer it home that there are never any guarantees, and any future-looking calculation is only an estimate. So if you are planning a new career, be almost pessimistic in your assumptions. If you work everything out based on 40 hour weeks and £35 an hour lessons, but end up with 20 hour weeks and £25 an hour lessons, you’re going to end up very disappointed indeed.

As soon as you try and discuss this with people, the first things they’ll say will be along the lines of ‘my car doesn’t cost me anything’ or ‘well I only spend £60 a week on fuel’. Or some other contrarian nonsense. I’ve explained the one about cars ‘not costing anything’ in the main Should I Become An Instructor article, and it is a nonsense claim as far as planning a career change is concerned. The amount of fuel you use is specific to you and the area you teach in. Someone in a big city, with all their pupils closely packed into a small area, might well have lower mileage (and lower fuel costs). Someone in the middle of the countryside will quite possibly have significantly higher fuel costs. In Nottingham, £100 a week is roughly what fuel costs are for me if I work for around 30 hours. And that’s a common ballpark figure for many instructors.

Play around with the calculations by all means, but don’t always look for the most attractive numbers. If you plug in a low fuel bill, low car costs, and top-end lesson prices, the result might seem wonderful, but at the end of the day you’re going to have to go out there and do it – and that’s where the hard work starts.

Just remember not to try and factor in tax, National Insurance, pensions, savings, bills, or anything else when trying to do a like-for-like comparison with salaried jobs. All that comes later when you have to deal with self-assessments and HMRC.

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