Codominant stems on trees: why they are bad. And good!

I came across this example of a co-dominant stem, while out walking the other day, and I thought I'd share it with you, partly because it's lovely in itself, and partly because it has a relevance to garden trees.

Here it is: 

... and hopefully you can see for yourselves what "co-dominant" means, even if you've never heard the word before.

Instead of the tree having one central stem, with branches growing out on all sides, it has two stems of very much the same size.

Usually, they grow side by side, and this is disastrous for the tree, because it causes a weak spot in the trunk, where the two stems originate.

Eventually, either one stem will break off, or the whole tree will split into two, which usually causes the death of the tree.

So if you plant new trees in your garden, you should always check, over the first few years, that they growing "properly", with one main trunk. And if you spot them deviating from this, you will need to prune out the lesser of the two stems, to allow the remaining stem to take over and become the "leader".

Unless it's a multi-stemmed Birch or similar, of course! 

In the case of the photo above, because it is a windswept position, the left hand stem was blown to the right of the - presumably - original main stem. Then, in a less windy phase, it grew back towards the sun, resulting in this interesting twining.

Such close contact has caused grafting, where the two stems "stick" together, so this particular tree will probably survive perfectly well: the grafted stem will be as thick, and nearly as strong, as if it had been just one proper trunk.

And the relevance to garden trees? If you have trees in your garden, don't let them start this game... unless you want to deliberately grow a tree with a decorative, twining stem. But be warned, it can take years before you see the result!

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