A Driving Instructor's Blog

Our Silver Birch in June 2017It’s late-February, 2019, and this article is already receiving a lot of hits.

The original was written in 2014, after my tree began to show yellowing in the middle of summer. It has been popular each year since, but in 2018 it went through the roof! The extremely hot summer resulted in heat stress in a lot of plants and trees, and Silver Birches were no exception.

The last week has been very mild, and the last two days have seen mid-double digits. I’m already noticing early season hayfever (tree pollen gets me) as a lot of blossom is starting to appear. I also noticed today that the first Hawthorn leaves are beginning to break out of their buds. They’re at least a month early.

Is this a warning of another very hot year? I don’t know, but I’m going to start the annual iron and feed treatment in the next week. I would also remind everyone that the last winter has been quite dry, so following on from last year’s heatwave, if it DOES get hot again the ground will have a head start on any heat-related issues.

Premature yellowing and leaf drop in Silver Birches can occur for the following reasons:

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

And it’s easy to get all three at once.

Back in 2014, our Silver Birch tree began to yellow and drop leaves mid-June! We were worried, and Googling for an answer was next to useless. Most of the technical advice was North American, and focused on the Bronze Birch Borer (a beetle that feeds on white birches), or the perils of trying to grow trees in either a desert or a swamp. Our trees had none of the beetle infestation symptoms other than leaf drop, and although the British never shut up about the bloody weather, we were not growing ours in anything other than normally-drained British garden soil.

After a lot of research, and after sifting out the crap, I discovered that yellowing/leaf drop is usually caused by deficiencies of nutrients and/or iron in the soil. In 2018, I further discovered that lack of moisture and/or high temperatures can cause the same symptoms – it’s called heat stress, and I’ll discuss it later (I wrote a separate article about it in August 2018).

Note that the problems described are not confined to Silver Birches. All trees and plants can be affected, though you may need a different fertiliser for those.

The problem we had in 2014 was characterised by bright, canary yellow leaves – just like in the Autumn – which began falling off the tree. Although the yellowing wasn’t as widespread throughout the tree as it is during Autumn proper, it was worrying all the same. I can’t honestly remember where I found this now, but somewhere in the hundreds and hundreds of forum pages and obscure “ask the expert” sites rattling on about the bloody Birch Borer I came across two easily-applied ideas that made absolute sense, and which could be implemented without calling in David Attenborough and Rentokil. Fertiliser and Iron Treatments

Nitrogen deficiency is resolved using ericaceous fertiliser (for lime-hating plants, which is what birch trees are). It is available from various manufacturers, such as Miracle-Gro, and can be bought from most decent garden centres and from many online retailers (including eBay and Amazon, where I usually get mine). It only costs about £5 a box of the granules, and there’s enough to manage a decent sized tree for at least half a season. You can also get liquid and slow-release varieties (since 2018. I’ve shifted to the liquid variety because of my new irrigator toy, and the slow-release kind would be great for those treating small plots of plants).

Normal fertiliser is no good for birches – it has to be the ericaceous stuff – and you just dissolve it in water and spread it around the tree. Remember that the roots extend outwards quite a long way and you’ll need to cover a wide area, but concentrate on the drip-zone (the area covered by the branches). The slow-release versions are just sprinkled on the ground and watered in, and they apparently work for up to 3 months (if I’m using them, I make sure I brush them into the gaps between paving stones, or the edge of the lawn – I wish they’d make the damned things in camouflage green, instead of the “hey, look at me all over the lawn” mix they actually are).

Leaves suffering from chlorosisLeaves that look like those in the images here are suffering from iron deficiencyknown as chlorosis.

Leaves are green because they contain chlorophyll (which is green). Simplifying the issue, chlorophyll allows plants to convert light energy into sugars they can use via the process called photosynthesis. Chlorophyll contains iron, so if there isn’t enough iron you get less chlorophyll (hence the yellow colour), and the plants compensate for lack of food by shedding leaves. That’s what you can see here.

Chlorosis is resolved using sequestered (or chelated) iron, such as Maxicrop, shown above. It comes as a liquid, and you can mix it with your fertiliser and water it in at the same time. As of 2019, I’ve discovered a source of Maxicrop in 10L tubs, which is more cost-effective than buying it in 1L bottles.

Close-up of leaves suffering from chlorosisSoil nutrient deficiency may also lead to new leaves being small and misshapen, instead of the classic Birch leaf shape. Some of ours were like that in that first season.

After a single application of fertiliser treatment in 2014, leaf drop stopped almost immediately once the already-dead leaves had fallen. The tree even threw out some catkins, which had been absent up until then. In 2015, I started feeding every few weeks from March with both fertiliser and iron and we had no leaf drop at all. In 2016, it was the same, with very fat catkins hanging from the branches, along with quite significant new growth. In May 2017 our tree looked like the photo at the top of this article, and here’s a close-up of the leaves from that year. Does that look healthy, or what?

Close-up of our tree's leaves in June 2017An additional iron treatment for the longer term is to water-in iron (ferrous) sulphate periodically. This replaces iron in the soil, too, but it also acidifies the ground over time, which is beneficial for ericaceous plants. It’s also very good for your lawn – iron sulphate is a moss-killer and a grass-greener (it’s sold for these purposes, and I use it several times a year to kill moss in the lawn).

Why does nutrient deficiency occur? Well, you have to bear in mind that when trees and plants die back in winter, the leaves they shed decompose and return nutrients to the soil as they do so. In urban gardens, though, leaves are usually swept up and taken to the rubbish tip to keep the garden looking tidy. Over time, the soil becomes depleted of those nutrients and you get problems like this. It’s fairly obvious looking at it now, but I was like everyone else in thinking that when you planted a tree you just forgot about it and let it grow – when it turns out you need to look after them almost as much as you would a tomato plant or an ornamental cactus!

You have to keep the treatment 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).

Now we come to the extremely hot summer of 2018. Around the end of June, I once again noticed a few sprays of yellow appearing. I wondered what was going on, but I immediately guessed 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 driven 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 in 2018 (and with the ground as dry as it was, it’d have been like trying to hammer a 6-inch nail into plate steel), so I resorted to 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 soil, and it fixed the problem in less than a week. How could I tell?

Well, with hindsight, all trees in 2018 had much thinner canopies than usual – heat stress isn’t just confined to birches. The leaves on my own trees were smaller than they were in previous years (and I have the photographic evidence of that). About a week after starting deep watering the tree produced some new shoots and the leaves that appeared were much larger. And some very fat catkins also appeared.

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. 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.

I would imagine that chlorosis could be reversed if it is caught early, since pale leaves are not necessarily dead – they’re just iron-deficient. In that case, you might be able to save some partially-yellowed leaves by applying the chelated iron treatment. I have a real example of that. In early June 2018 (before the heatwave really kicked in) I noticed my neighbour’s usually-dark green Cherry Tree leaves were very pale and many yellow ones were falling. I told her about the iron treatment and she bought a bottle. The leaves on that tree are now dark green again and no more have fallen.

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.

Treat your trees from March until September. Feed at least once a month (even two to three times during the earlier months) – and water regularly in hot weather anyway, as they do need moisture.

How often should you feed?

I initially started doing it once a month in the first season, and carried on at the same rate into the second and third. However, I now do it twice a month because one year – and I can’t remember which – towards the end of the season I noticed a few signs a chlorosis about a month before the normal autumnal change.

Can heat and drought cause them to lose leaves?

Yes. If they are stressed you may get them dropping leaves, and if not treated the leaves can even go brown and die on the tree (I saw a lot of Silver Birch trees on road verges like that in 2018). 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.

As I explained above, the hot weather we experienced in summer 2018 caused my tree to show a some yellow leaves. I commenced deep-watering from June, as well as feeding regularly. This was the first time heat/drought has been a problem, so it caught me out a little. However, after a week of deep-watering leaf-yellowing stopped completely, and the tree was healthy throughout the rest of the heatwave (as was the lawn, which was parched brown, but ended up lush green).

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.

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?

The short – and very obvious – answer is: in the Autumn. It can vary a little up and down the country (just as Spring tends to start earlier the further south you are), but in the Midlands they usually start to show sprays of yellow from late September to early October. 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.

In 2016 (almost overnight during the first week or so into October), ours produced a lot of yellow on the inside, whereas the outer canopy remained green – it looked rather nice. The neighbours’ trees had much sparser canopies than ours and they had clumps of yellow all over. Astronomical Autumn officially begins sometime towards the end of September in the UK (meteorological Autumn starts in early September) and you probably can’t do much to fix your trees after August if you’ve got the early yellowing problem. I’d still recommend a good feed or two, but not beyond the end of September. But be ready to start feeding from March.

It’s worth noting that a few isolated yellow leaves on a tree which fall in windy weather are not really indicative of a major problem. When you have sprays of yellow, or if you’re losing dozens of leaves in one go, that’s when you should take action.

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 have a problem – probably one which can easily be sorted by reading through this article.

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 have now invested in 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.

I do this up to twice a month between March and September. In 2018, I was deep watering every night during the heatwave.

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.

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 have a pair that have nested near us for the last 10 years or so. 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 2019 they are actively nest building (it’s usually March, but the warm end to winter has kicked them off early). They will carefully select the twig they want, but the sods will tear off loads more before they find it.

I watched one on a dead Birch tree when I dropped a pupil off last week. He (or she) had broken off a bloody big twig – almost a branch – and was trying to get into a position to fly out of the branches with it.

Also note that we’ve had some high winds recently (2019) and that might knock a few loose twigs down.

My tree is taking a long time to show any leaves

I’m not an expert, but if this happened to me – and knowing what I know now – I’d start feeding it pronto. Of course, it might just be slow – some trees do seem to lag behind others – but a good feed can’t do any harm. Mine was in full leaf by May 2018, whereas neighbour’s trees were still in the process of producing leaves judging from the light that came through their canopies. In hindsight, and following my observations throughout the year, the heatwave seemed to have stressed trees to the extent that their canopies were sparser than usual (leaves were smaller), and this may have been what you were experiencing.

In the worst case, your tree might not be in good condition at all, but you’d have to call the experts in for that.

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 started sprouting a week or two earlier than the neighbours’ trees in 2018, and the foliage on mine is much denser. The catkins came before the leaves.

I strongly recommend feeding them regularly as a matter of course – and watering if the ground is dry.

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, anyway.

In hot and dry weather, many trees can become “distressed” and start to shed leaves. Silver birches are affected by this. Also, greenfly infestations can cause leaves to die and fall. If a lot of leaves are turning yellow on the tree then you have a problem – quite possibly one of those which are the main subject of this article. However, a few leaves falling is probably nothing much to worry about.

In 2016 the first show of yellow up here on all trees was during the first week in October. In 2017, yellowing began a month earlier, and by mid-September they almost all were clearly changing. In 2018, some birches dropped their leaves in August and were suffering well before that as a result of the hot weather we had. However, my own tree has begun to turn in the last few days of September, along with many neighbouring trees, which is entirely normal. July yellowing is not due to autumnal changes.

Do Weeping Silver Birches lose their leaves in Autumn?

Yes.

When do Silver Birch leaves go all brown?

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

I’ve had quite a few visitors from this search term, 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 going to be a universal issue. You might need a different fertiliser to address any nutrient problem, but iron will likely fix chlorosis.

Recently, someone found the blog as a result of premature leaf drop in their Betula utilis. This is the Himalayan Birch, famed for its peeling paper-like bark, and it is a member of the same family as the Silver Birch. In the Himalayas, it often grows among Rhododendron plants (look at that fertiliser again – are you seeing the connection, here?), so the advice given above would work for the Himalayan Birch, too. And it also worked for my neighbour’s Cherry Tree, as I mentioned earlier.

(1 views today)
Share