Less invasive alternatives to willow for living structures

Question

I want to create a living willow arbour (something like this: https://commons.wikimedia.org/wiki/File:RuddSeating.JPG). However, it would be only 6-8m from my house, and around the same from two underground sewage pipes.

Am I right in thinking this rules out willow, as the roots are likely to cause problems? Or would the aggressive pruning involved in maintaining such a structure (say 2-3m across) limit the root growth?

If willow is likely to be problematic, are there any suitable alternative species? Ideally they would be:

• fast growing
• producing long pliable stems
• tolerant of pruning
• easy to root from cuttings

I am in central UK, with clay soil.

Answer 1

Most species that are good for edges (so that they allow strong pruning) should work. Maybe try not to use species which produce too much wood.

(Many) willows likes humid places, so there is a risk that they will spread roots. But you can choose some willows which naturally will not growth much (so also roots will not growth so much). Salix purpurea (purple willow) will grotwh just few meters, other "small" willows: Salix triandra (almond-leaved willow), and Salix caprea (goat/pussy willow) are relatively small, so with less problem with roots. For sure, you should not plant the larger willows (and not the smallest willows, which are just few centimeters tall).

Hazelnut tree (Corylus avellana) is also an option: you should prune away all large trunks, but it is a lot flexible (and shrub like), so you can construct a similar hut.

Or you may choose corn (Zea mais): this will live only for summer to winter, and you need to replace it. Just you can choose different form every year.

Answer 2

You are wrong in thinking that it rules out willows. I have to do root influence calculations regularly as part of my job (landscape architect).

Firstly, willows and any other trees are unlikely to crack a pipe. All roots start as tiny threads that grow through the gaps in the soil, they do not possess jackhammers to make their own cracks. If the pipework is sound, then they will not penetrate it. It is true that once they have grown through a pre-existing crack they will eventually thicken causing damage. However, in your case...

The next thing to consider is that the influence on foundations tends to be related to the effects on soil shrinkage. During the summer, a large tree can remove a large quantity of water from the soil. If it is a high shrinkage soil (such as clay), this will cause it shrink. In winter, when they shed their leaves and rain saturates the soil it will expand again. Over time this will cause heaving of the soil. The amount of shrinkage a particular tree or shrub will cause is in part related to their water demand and in part due to their total leaf area (i.e. the bit that gets rid of the water). In the case of willows, they are high water demand trees, meaning that you would need to site them further from foundations than many other trees of the same size. In your case, limiting their height to 3m would mean you should be safe to plant them 6-8m from foundations. Limiting their height will also limit the distance their roots grow thus reducing the risk of invading damaged pipework.

You do not want an overly vigorous cultivar as you will forever be pruning it and your structure will become woody and end up being rather short lived. You do want something that is going to be pliable and not branch too much. It is worth contacting a supplier of living willow and discussing the details of your project with them. I disagree with one of the posts that says willows like humid conditions. Admittedly, some do, but not all. Salix are highly diverse and can be found in habitats ranging from deserts through to tundra (both of which are not at all humid!). Salix exigua might be a good candidate it is hardy in the UK, very beautiful and drought tolerant.

Another answer mentions hazel. I haven't seen it used before for this purpose, however, it does produce quite pliable straight rods in the first year after coppicing. It is slower growing and is a low water demand species. It does not strike readily from cuttings though, so you would need to plant plants rather than rods as this case for willow.

See NHBC root guidelines

Answer 3

An ivy should do well although you would need some structure, like wire , for it to climb. English Ivy comes to mind ( although invasive here in TX) .

Answer 4

Root problems are situation dependent. Roots can be a problem:

• Sewer lines of the old pipe and gasket sections. Often they leak, and the joints can be invaded by roots.

• Foundations that are not cast concrete. Either stone and mortar or concrete block and mortar can be penetrated by roots.

Modern sewer lines are glued plastic, don't leak, and are not a problem. Similarly a cast concrete foundation is not a problem, assuming that it is deep enough that roots are not UNDER it.

You should be able to ask your local agricultural agent (In the U.S. it's your County Extension Agent, in Canada it's your County Agricultural Field staff) about the soil types in your area, to find out if clay heaving with changes in water level is a problem in your location.

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That said: I have lived in several houses with shrub form willows adjacent to the house -- within 2 feet. Have not had foundation issues.

I would suggest working with one of larger shrub willows -- Common Osier willow perhaps.

Edit: See this document: nhbc.co.uk/Builders/ProductsandServices/Standardsplus2019/#40

for advice on working with trees and foundations. While my own experience has been generally favourable, the use of trees near foundations that have significant clay can create problems, especially if your yearly rain cycle alternately dries and saturates the clay.