A Driving Instructor's Blog

Our Silver Birch in June 2017There is a special problem to look out for this year! The original article dealt with chlorosis and nutrient deficiency, and while this is still a potential issue, it is the hot weather which is causing problems right now.

I’m updating this in early summer 2018. After a great start, the weather has turned very hot and this is stressing trees, causing some leaves to yellow. So as well as the advice given below, don’t forget to water your trees regularly – and I mean deep watering, so it gets down to the roots. I’ve written an article about heat stress here. Trust me: heat stress is a significant problem, certainly in 2018, but also in any other year where there is a lengthy period of warm, humid, and low-rainfall weather. That’s something new I have learned.

From observing other trees this year, I also suspect some individual trees are more susceptible than others to heat stress – and possibly even the nutrient issue discussed below..

The article has been increasingly popular each year since I first published it in 2014. I’m feeding my trees every couple of weeks at the moment (2018) and they’re now in full leaf. However, after a couple of weeks of very hot weather, we got some yellowing literally overnight. The remainder of this article deals with nutrient and iron deficiency. Read the article about heat stress for additional problems in 2018 (and deep watering definitely DOES have a significant affect after only one week).

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 garden soil.

After I first wrote this article, I discovered that yellowing/leaf drop can be caused by two different things. You can’t do any harm if you just apply both of the remedies I uncovered, though.

The type we had was where the leaves turned bright, canary yellow – just like in Autumn – and began falling off the tree. As I said, it started in mid-June, and although the yellowing/leaf drop 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 ideas that made absolute sense, and which can be implemented without calling in David Attenborough and Rentokil.Fertiliser and Iron Treatments

Summer leaf-drop and leaf yellowing is caused either by a deficiency of nitrogen in the soil, or a deficiency of iron (or a combination of the two). It affects many plants – not just silver birch trees. Note also the comments above about watering – prolonged dryness/drought, such as we are experiencing in 2018, can also lead to yellowing as the trees become stressed.

Nitrogen deficiency is easily 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 get mine). It only costs about £5 a box, 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.

Bear in mind that normal fertiliser is no good – it has to be the ericaceous stuff – and you just dissolve 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 granules of the same fertiliser are just sprinkled on the ground and watered in, and they apparently work for up to 3 months.

Leaves suffering from chlorosisLeaves that look like those in the images here are suffering from iron deficiencyknown as chlorosis. This, too, is easily dealt with by buying some 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 all in one go. Plants need iron to produce chlorophyll, and since chlorophyll is why leaves are green in the first place, not being able to produce it means leaves become less green and take on a yellowish hue, especially when lit from behind – eventually looking like those shown.

Close-up of leaves suffering from chlorosisAny soil 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 2014.

In our case, 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 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 good 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).

You have to bear in mind that when trees and plants die back in winter, the leaves they shed return nutrients to the soil as they decay. In urban gardens, concerns over appearance mean that people usually sweep up the leaves as soon as they fall – so nutrients end up being removed from the garden and transferred to wherever the refuse collectors take them. Obviously, your trees and plants suffer the most, which is why you need to give them this extra help to recover what they have lost.

Well, I say “obviously”, but it’s funny looking back, now. I used to think that if 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! Judging by the increasing number of hits I get on this article, a lot of other people are discovering the same.

A final few words. You have to keep the treatment going about once a month between March and September, and you have to follow the same routine each year (or at least over alternate years). Also be aware that in very hot weather or during drought trees can become stressed and a leaves may yellow and drop for that reason alone. This isn’t too much of a problem, and a weekly deep-watering is all that’s required (hosepipe bans notwithstanding).

A final word: It is 1 June 2018, and my trees have not shed a single leaf so far.  My neighbour has a well-established cherry tree (or something which gets pink blossom, anyway) – they’ve had it for decades. It is dropping yellowed leaves already, and the leaves still on the tree are noticeably pale where in all previous years they’ve been dark green. They keep their garden spotlessly clean, thus removing fallen leaves each year as soon as they drop. It’s a clear case of chlorosis and/or nutrient deficiency.

Can you rescue leaves which have turned yellow?

No, probably not. Not the ones which are canary yellow, anyway, since they’re already dead and will have to fall off the tree. How long that takes will vary, and a little wind can speed things up. The important thing is that by feeding the tree you can stop any further yellowing – and believe me, the first time you do it the effects will be quite noticeable.

I would imagine that chlorosis could be reversed if it is caught early, since the yellowing is not due to leaves dying – they’re just iron-deficient. In that case, you might be able to save some yellowed leaves by applying the chelated iron treatment. However, if not treated then the leaves do die and fall off easily once they are predominantly yellow.

Do you have to keep treating the trees?

Yes. If you don’t, the problem just comes back depending on how long the previous treatment lasts for, and that is dependent on how bad the deficiency is, how big your trees are, what else is growing there, and how your soil drains when it rains. Huge trees will suck up all the nutrients, and if you’re raking up and binning the leaves each year nothing gets returned to the soil. It stands to reason, really, but I was as blind to it as anyone else until I encountered the problem.

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 autumn change.

Can heat and drought cause them to lose leaves?

Yes. If they are stressed you may get them dropping a few leaves. 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.

Let me point out that the hot weather we’re experiencing as of the start of summer 2018 caused my trees to show a some yellow leaves. I commenced deep-watering from June, as well as feeding as described elsewhere in this article. This is 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 trees are now looking healthy again (as is the lawn around them, which was parched brown).

Is there any other way to deal with the problem?

You have to get nutrients and iron back into the soil. 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 early October. 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.

Autumn officially begins in mid- to late-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.

How do you apply these treatments?

You make up the required solution as directed on the pack, then water it into the area specified. A single watering can is usually spread over 10 square metres (a medium sized tree probably requires watering over as much as 100 square metres). You can also buy mixer units which have a small tank and connect to your garden hose. You put the concentrate into the tank and the device mixes it with water as you spray the ground under your trees.

What I do is make up a concentrate in a 5L measuring container, then use 1L of that in a 15L watering can topped up with water. It’s quicker this way. I put 250g of Miracle-gro and 250mls of Maxicrop in the container (marked with 1L divisions) and make up to 5L with water. Once dissolved, I just pour out 1L into my watering can, top up from the garden hose, and evenly spread it over about 10-20 square metres, making sure I include flower beds as well as the lawn. I do it at least once every four weeks throughout the growing season (March-September), though I’ve upped that to fortnightly this year.

For the iron sulphate, I dissolve 375g in water in the measuring container made up to 5L, and again use 1L portions in my watering can made up to volume from the hose. I apply this treatment once a month or so – staggered with the fertiliser treatment. Iron sulphate at this concentration will kill moss within a few hours, so don’t worry about any black patches that appear on the lawn – it’s just dead moss, which can be raked out.

I try to time applications of fertiliser to just before (or during) rain to be sure it is fully watered in where the trees can get at it. Otherwise, I put the sprinkler on for a bit. I let the iron sulphate go to work on the moss and let the weather take a natural course – acidifying the soil is a longer term thing.

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.

Another likely problem, though, is crows. Yes, the winged variety. From March they will be nest-building, and they are very, very selective in their choice of twigs for the purpose. We get great amusement watching 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.

Mind you, I’ve never seen a crow carry off a branch – they stick to the smaller stuff – so if your tree is dropping large branches you might need to get a tree surgeon in to have a look at it.

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 is in full leaf now (May 2018) whereas neighbour’s trees are still in the process of producing leaves judging from the light that passes through their canopies.

In the worst case, it 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.

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 also cause leaves to die and fall. If a lot of leaves are turning yellow on the tree then you have a problem – quite possibly the one which is 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. July yellowing is/was not down 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.

If leaves are brown and dead then that’s not a good sign. I’ve had quite a few visitors from this search term, and when I looked it up it seems that extreme cases of chlorosis can result in leaves turning brown. 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.

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