Sunday, 15 August 2021

How To: prop up a Mulberry tree

Anyone who has inherited a Mulberry tree will know about this problem - they are lazy trees, which grow to a certain size, then lose interest in being upright trees, and decide to lie down and take a rest. 

Here's a typical example, below: ten years ago, this one was leaning at only about half the angle which it has now achieved.....

 .... and I watched it fall over, in slow motion, over this period.

(I do wish I'd taken a photo every year, then I could have made a gif of it leaning gently over!)

When I first started gardening there, I used to be able to weed all round the main trunk - without bending over!

Now, as you can see, there is barely room for a daffodil.




 Here's another Mulberry, right: much larger and older: 

In this case, the Client had had a tree felled, elsewhere in the garden, and used large sections of the trunk, as props. 

You can't see the bases of the props, but they are each standing on an old concrete slab, which serves to spread the weight, keep them stable, and reduce rot. And of course, as soon as the underplanting grows, they are quite invisible.

It's best to keep the limbs off the ground if you can, because lying on damp ground tends to make the older limbs rot, which is not a good thing.

They do also sometimes root themselves into the ground, but that isn't really a problem as such - in fact, you are making new Mulberry trees! 

But really, it's best to keep the branches where they belong, up in the air.

So, why am I suddenly telling you about Mulberries?

Answer: I had a question from Graham (*waves*), who has a very old Mulberry tree, with a habit of occasionally dropping large branches, and which now has a Branch of Damocles leaning right across the main garden.

Graham said that he'd had a tree surgeon in, who said he was sorry, but "he hasn’t the structural expertise in propping up large tree branches".

At first I was a bit, er, scornful about this, because the routine is quite straightforward: just find a stout wooden post, or a non-decayed branch (preferably with a fork at the top) then wedge it under the offending branch. 

Here's a nice, simple example - left. 

A branch with a fork at the top, wedged neatly underneath a drooping branch.

Here's another, on the same tree - right.

You can see that it's a very stout, forked branch, but not very long... so I used a second piece of wood (stolen from the woodpile!) underneath it, to raise the fork as high as I could. The weight of the branch holds it all very firmly in place.

It definitely helps to have at least two people: one (or more) to lift up the branch slightly - if there is still any "give" in it - and the other to ram the post underneath. 

I went on to say that if the branch is seriously huge, and you cannot lift it at all, then simply choose larger supports - very much the sort of thing shown in the pictures at the beginning, which were sections of trunk from a large tree - and put them in position, using additional smaller "slices" or discs of wood, in order to get as high as possible under the drooping branch. Then allow time and gravity to lay the limb down onto the support. 

You can see that here - left - I used two slices of a felled tree (again, stolen from the woodpile), to prop up this overlong branch.

In this case, Mr Client was around, so I got him to lift up the branch, as I slid the second slice of trunk into place.

So there you see the principle: any old branches will do, as long as they are stout, and are in good condition, and they should last for several years.

As the trees will continue to grow, props will often need to be re-positioned every few years, so this gives you the opportunity to check them for decay, and replace them if necessary.

But then Graham showed me pictures of the tree in question: ah! I see the problem! Not only is it a whopper, but the offending branch is currently a good 9' (3m) off the ground, so although the principle of the "prop" is sound, it simply would not be possible in that situation. Any prop would need to be quite massive, and would need to be set in concrete (not exactly in tune with a garden!) and even then, it would not be structurally sound. 

Further, the branch is growing very nearly horizontal to the ground: and it was clear from the photos that it was pulling away from the main trunk of the tree, so there was every chance that the whole branch would just shear off, at some point.

So, with regret, my advice to Graham was to get the tree guy in again, and instruct him to reduce the offending limb, quite significantly.

I always feel like a murderer when I say this, but there are times when a tree just has to be reduced, and as Mulberries are notoriously prone to splitting, and sinking, and dropping branches, and collapsing in slow-motion: well, it might be better for the tree, to have some of that weight removed.   

The options then are twofold: either remove one entire branch, right back to where it joins the tree. There are many advantages to this: it's a clean cut, it deals with the problem for all time (well, for that particular branch, at least), and it can open up the canopy to let light in to the centre of the tree.

But on the other hand, it might leave a big hole in the canopy... in time, the tree will fill in any hole, but sometimes Clients are a bit twitchy about having too much removed at once.

In which case, a solution is to assess the branch, to see if there are any side branches, closer to the trunk, which are growing out at a "shapely" angle. If there are, then the branch can be shortened to that point, which takes the weight off the branch: in fact, when you start to reduce a large branch, you can often see the limb visibly lifting, as the weight is gradually removed.

When I say "a shapely angle", this is something which is a bit hard to describe without using my hands: it means a branch which is heading off from the original branch, in such a way that it can take over the job of "leader", thus retaining the original "form" of the tree.

I would expect an arborist to be able to advise as to which limbs to keep, and where to cut: the essence is to get the weight/bulk off, but to try to retain something of the "form" of the tree - and to get it back to being a more upright shape. If possible...

Finally, we turn to the knotty problem of WHEN to prune a Mulberry. They are subject to leaking dramatic amounts of sap, if pruned at the "wrong" time, so it's important not to rush out there and chop bits off them at random: any worthwhile arborist or tree surgeon should already know this, but it's worth mentioning it again.

Some quick internet research throws up some contradictory statements:

1) "Winter pruning can be performed from November to early March, though we recommend pruning in early March, just before growth recommences."

2) You should only undertake pruning when the tree is dormant, roughly 1 month after the leaves have fallen. (they fall in November, so that's a vote for December-ish)

3) Prune mulberries when they are fully dormant; about a month after leaf fall. (this is the RHS website, so I'd agree with that one.)

4) Try not to cut branches larger than 2 inches (2.5 cm.) in diameter. (Yes, that's not very helpful, we often have to do things, because they need doing...)

5) Don’t prune when the weather is very cold. When the temperature is under 50 degrees F. (10 C.), it is harder for the tree to seal off its wounds. A good time for mulberry trimming is in spring prior to the buds turning green. ("Spring", eh? That's traditionally April or even May...)

6)Prune towards the end of dormancy, in early March.

7) Although most trimming should be done in winter, you can do some selective trimming in the summer if your tree is growing too much for your liking. For example, you can trim off the top of the tree in summer to control its height. (that's from Wikihow, so it must be true, right?)

8) February is TOO LATE to prune sap bleeders such as Birch, Walnut, Mulberry etc.

Confusing, huh?

There is another Mulberry pruning issue: many of the internet entries stress that, even if you do it at the "right" time, you should only do minimal pruning: the figure of "only cut branches not more than 2 inches in diameter" keeps cropping up.

This chap, in direct contradiction, says "And remember – you can chainsaw a mulberry to the ground and you won’t kill it. They’re amazing.... Unlike some other fruit trees, mulberries can take a ridiculous amount of pruning and shaping."

So, after all that lot, what do we think? 

Well, it's much easier to do the work when the leaves are off the tree, ie the depths of winter, because you can see what you are doing. I think we all agree on that.

But on the other hand, sometimes you just have to do the work, if the tree and/or the Client requires it, regardless of the time of year.

And, as always, a penn'orth of prevention is worth a pound of cure, as they used to say, so if you have a Mulberry tree in your garden, check it over at least once a year, and see if there are any branches which need attention. Mark dead or damaged branches, to remind you which ones to remove, at the end of the year, and prop up any which are starting to droop.

Finally, really finally, here's a scary thought:

Did You Know? In 1984, the city administration of Tucson, Arizona, banned the planting of mulberry trees citing that the amount of pollen produced by these trees was harmful for humans...


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