Grafted Japanese Maples: look out for them reverting!

First the botany lesson - nearly all the miniature Japanese Maples which are sold today are grafted trees: and if you didn't know, grafting is the process whereby two compatible plants are cut-and-pasted together.

It means that a "beautiful" top is grafted on to a "less beautiful but very sturdy" bottom, in order to produce large numbers of spectacular plants - in this case, trees - as quickly as possible.

The top part - the "scion" as it's called - is the part we want to own: it may have shapely leaves, or fantastically coloured leaves (or both, as in this Acer palmatum dissectum, left!), or it might have a weeping habit, meaning that the leaves droop over and downwards, instead of growing upwards. 

And yes, our dear friend the Salix Kilmarnock (of which I have written many, many articles... just type Kilmarnock into the Search box, top left of the screen) is in that category, it's a weeping, grafted tree.

The bottom part - the "rootstock" is usually something quite ordinary, but something which is sturdy,  reliable, not prone to disease etc.

And the problem arises when the bottom part, the rootstock, decides that it's time to get in on the action, and produce some shoots of its own. 

Why is this a problem? Because the rootstock is often - not always, but usually - so very vigorous that it will take over the entire tree.

Salix kilmarnock are little devils for this, and I have written about them several times: but it also applies to a lot of the decorative Acers, or Japanese Maples.

Here's one I encountered a couple of weeks back: the top part is a very nice purple-leaved variety.

 

 Ah,but look lower down: what's that, right at the very bottom?

There, can you see it?

It's a cheeky little sprout of non-purple leaves, which means that this part of the tree is not the same as the upper, purple-leaved part.

And yes, this sprout is clearly growing from below the graft point.

Here's a better shot of the actual graft.

Can you see that deep V-shaped wedge?

That's where the upper part, the scion, was sharpened - rather like a pencil -  and pushed firmly down into a carefully-prepared split in the rootstock.

That is a somewhat simplified explanation, but that's basically how it works. Then the whole join is wrapped in grafting tape until the two parts knit together and become one tree. 

It's coincidental that the scion, upper, part has rather gray bark, while the rootstock part has bark that appears to be very much whiter, but it does make a good illustration of the mechanism of grafting.

And the problem, of course, is that if we left this little sprout, it would flourish and grow, which would make the tree look a bit odd: all purple up above, then this one colourful branch down below.

Plus, because the rootstock is generally "stronger" than the scion, it is likely to grow very vigorously. Often, when this happens, the growth above the graft then dies off, because the resources of the tree are being pushed into that vigorous lower branch. 

So when we have grafted trees, it's important to keep checking for any low-down sprouts like this, and to remove them as soon as they are seen. When they are tiny, like this one, you can gently pull them away from the trunk: any bigger and they will need to be cut off with secateurs, to avoid damaging the bark.

And yes, having spotted this, I am now going to weed and top dress the pot, as well!

 

 

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