How close can you plant Willow trees (and other vigorous, damp loving species such as Poplars and Alders) to a house or drain?
The easy answer is “not close at all” to any drain, including modern drains, or old house. If there is a way in, willow will almost certainly find it.
Yes, we also have a friend who had an uncle whose dentist had a willow next to her well, and it was fine, but these exceptions only prove the rule.
A golden weeping willow is as beautiful and delicate in the breeze, but there is a monster lurking below.
Willows have to be the all-time root producing world record holders, and Alder and Poplar aren’t far behind. Their tentacles will sniff out water and drainage pipes at long range.
Even if the roots cannot get in at first, there will be condensation on the pipe that encourages the roots to wrap themselves around the pipe like a sleeve. Perhaps the roots dowse for the water, who knows.
This should not an issue if the willow is squat and stable, but a tall tree that sways in the wind will tug at pipes wrapped in its roots, potentially working a gap loose for them to enter the pipe.
And if that tree falls over in a storm … messy.
Without knowing for sure what their maximum reach is, I think it’s wise to leave at least 10 metres between tree and drain: 15 metres feels better.
The company Water Willows, supplier of fine unrooted willow cuttings, gives these willow planting instructions:
“Do not plant willow close to buildings, walls, stone structures, drains & septic tanks where their roots may cause damage, as willow needs plenty of water and the roots actively seek it.
We suggest a planting distance of 1.5 times the maximum height that the plant will be allowed to grow. This applies to cuttings, whips, rods and trees, especially the more vigorous varieties.”
Which brings us to a good argument that goes like this:
- Most tree roots extend underground only a bit further than the canopy’s shadow above ground.
- A smaller canopy means (in theory) smaller roots.
- So by pollarding your willow to keep it small, it won’t be a danger to drains. Happily, pollarding willow is a common garden practice.
That all sounds good, but this horror movie, available to you only here, shows you why your mileage might vary.
The Willow from the Black Lagoon
This poor little grey willow, Salix cinerea, which produces some of the most beautiful catkins, was only looking for a better life in someone’s drainpipe.
It was 2-3 years old, pulled out by a friend of Rebecca, who works here and brought the creature in.
Those roots are well over 3 metres long, while the scrappy little plant is only 1.5 metres above ground.
The root mass is perfectly tubular and solid: a real tug of war to get it out, and another year would probably have seen it a metre longer and completely immovable.
So, if you see drains growing near your willows, it’s probably better to get someone to do something about it.
Wow, a willow monster indeed – if we could grow carrots like that we’d be very happy….must sow some in the drain pipe next year! 🙂
The roots of a plant cannot get into drains that are not damaged. If no water can leak out, there is no way the plants can detect the water inside the pipe. Planting near a drain may be a risk – it is not always possible to know if drains are damaged – but providing the pipes are sound, the roots cannot get inside the pipes. If the pipes are cracked, any plant root is likely to block the pipe in time.
You are correct of course. And generally modern drains are plastic and leak free.
The purpose of the willow root in drain video was first to show the astonishing mass of root that one seemingly small plant can produce and second to make people aware of the RISK of planting trees close to drains. It is a little bit like planting trees too close to foundations. IF the foundations are concrete and IF they are uncracked, then tree roots are most unlikely to do any damage. But the tiniest crack and a root will find it. If it is the root of a long lived woody plant, it will oven the crack just as if someone was smashing a wedge into it with a pile driver. It just takes longer. So we never advise people to take the risk.