Kilmarnock Willow and the Behaviour of the Roots

Aha!

Today we have a NEW question about Kilmarnock willows!

I'm all excited about this, because usually I get the same old questions, and I just refer the enquirer to this site, and suggest they type the word "Kilmarnock" into the Search box - top left of the screen - to find all the information they could possibly want on the subject.

But today, all change, we have a NEW question!!

Well done, Matt.

Matt's question concerns the roots of a Salix 'Kilmarnock'.  He asks what the general rule is with the classic "willow seeks water, busts drains to get it" routine, with regards this species.

He continues - and this is the exciting "new questions" part -  "I get that its a grafted rootstock man-made thing, so I'm guessing its not like a proper willow as, effectively, the base is different but have you pulled any of these out and seen how large and/or invasive the roots tend to be, or do you know if they're fine around drains in general?

Oddly enough, the fact that they are grafted actually DOES mean that they are like a proper willow: the upper part is the "fancy" weeping part, the lovely part, the small and dainty part: but the rootstock is common old Grey Willow, Salix caprea, which is indeed a "proper" willow, and which will turn into a full sized tree, given half a chance.  

(For more information on what constitutes "half a chance", and how to prevent it, just check any of the many other articles about Salix 'Kilmarnock', which you can find by typing Kilmarnock into the search box, top left of the screen.)

 Part one of my answer for Matt is therefore this - here's what I said in one of my many posts on the subject: 

1) Roots. It is always wise to consider roots, when planting trees. Willows in particular have a reputation for invading drains, in their search for water, so it's never a good idea - generally speaking - to plant any sort of willow too close to a house, or a building of any sort. 

Salix Kilmarnock is a bit of an oddity in this respect: because it is a grafted tree, and the upper part is very small (compared to a "natural" willow), the roots don't need to grow to full size to support it, so they can be planted in, for example, small front gardens. However, if you read some of those other articles I've written, you'll learn that one of the problems with grafted trees (indeed, with any grafted plant) is that of "reversion", where the rootstock sends out new growth which, if unchecked, can take over the whole plant. 

So, a case could be made that it is never "safe" to plant any sort of willow tree too close to a house, just in case the owner fails to notice it trying to revert, until it has grown into a proper tree and possibly damaged their drains.

And part two of the answer - have I ever dug one up, and if so, how big were the roots? Well, that's the truly interesting question, and the answer is no, I've never personally dug one up. I've recommended it a few times ... (*laughs*)

I've thrown out a couple which were in pots, but that does not really answer Matt's question, as the pots themselves were restricting the roots.

In several cases, I've seen trees in pots - not just Kilmarnock, all sorts of trees in pots - escaping by pushing a root through the drainage hole(s), which then roots itself into the ground. These roots can become quite substantial, but they will never compete with the roots of a tree which is freely planted in the ground.

One final aspect to consider is that trees tend to form roots which are proportional to the size of the tree: so a "big" tree will have a "big" establishment of roots. A Salix Kilmarnock will be, to some extent "dwarfed" because the upper growth is not as extensive as it would be, if it were not a grafted tree.

So a small Kilmarnock in your garden should not grow anything like the extensive amount of roots that it would, if it hadn't had the top cut off and some weeping branches grafted on.

BUT!

It is still a willow, and it will still have the capacity for growing.

So I stick by my advice in the section reproduced above: "it's never a good idea - generally speaking - to plant any sort of willow too close to a house, or a building of any sort".

If you plant a Kilmarnock in your front garden, and if you keep a careful eye on it for ever more, and if you don't ever let it revert... then your drains SHOULD be ok. 

But I take no responsibility for this comment, whatsoever!!

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