Trees, Roots and Landscape Drainage

[M.D. Vaden]

After browsing a lawn & landscape forum's threads on drainage, and a couple of old ones here at A.S., seemed worthwhile to start one here in the tree forums. It's evident from many older replies that emphasis is often on how to install, say, a French drain, rather than whether that kind of drainage is needed or not.

I just started rewording an advice page I started a few years ago for Portland drainage, especially after moving photos around on it. This month, I hope to add a bit more about trees and roots in relation to drainage.

One surprise in the past couple of years, was how fast tree roots can grow into a perforated drain pipe. I already knew roots can get through fabrics and into the pipe and eventually completely clog it, but just didn't realize they could start getting in there within 365 days.

On my drainage page, the attached image is included, to show how roots can enter drainage in merely a year. Went through fabric a landscaper lined the trench with, through the drain / river rock, through the next fabric wrapping the perforated drainage pipe, and passed across the ID / inside diameter of the pipe. No solid root barrier of any kind.

For my own projects, if I need to gather water near trees, sometimes I resort to catch basins for this reason if it's practical. When moving water near trees, I usually pass them with solid. And when a French drain is near tree and shrub roots, root barrier panels, bamboo root barrier and pond liner all seem to work pretty good for lining at least the tree root side. This is for surface water, not sideways or laterally moving water.

 

[M.D. Vaden]

This was a recent ordeal from around October. The small willow species in the middle was dug around the day before the photo, because I was planning to raise the center grade there by about 8 inches, and contour the new replacement lawn convex, sloping to the edges. The standing water in the hole is from overnight rain, and that was the first measurable rain Portland got since approximately early July.

In the right corner, there are trees on the other side of the fence, so I lined the French drain on that side to block roots. The willow is small, and they plan to prune it to keep it small, so I opted for bamboo root barrier around it to hinder it's roots passing through sod toward the French drain. And the willow was raised at least 8 inches.

The whole lawn is now convex, but the shot was taken from about 14 feet up off an orchard ladder so it may not look that way.

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