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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Slope stabilization and soil erosion, Tree identification, Populus

When a cottonwood tree is cut down, does the stump die, or does it send out shoots that grow into more trees?

And, if a cottonwood tree located on a hillside is cut down, what is the risk of erosion?


As it turns out, some poplars and cottonwoods sucker from the roots and some do not. Determining what kind of cottonwood you have is the key to answering this question.

Identifying tree varieties can be tricky. The best way to get a positive ID is to take a sample to the Hyde Herbarium at the Center for Urban Horticulture (near the University of Washington). It is definitely worth a visit, as it is the only herbarium on the West Coast that serves the public.

Hours, driving directions, how to collect specimens, etc. are on the Hyde Herbarium page.

As for your second question, here is what the Washington State Department of Ecology's Vegetation Management: A Guide for Puget Sound Bluff Property Owners has to say (p.25):
Given the importance of tree cover on potentially unstable slopes and the advisability of retaining them for erosion control purposes, a landowner should explore alternative options to tree removal or topping...[if a tree must be cut] stumps and root systems should be left undisturbed...[to reduce the risk of erosion].

A companion website from the Washington State Dept. of Ecology contains a great list of groundcovers, shrubs and trees that will help keep your slope intact if you decide to remove the cottonwood. The website includes a Plant Selection guide.

Date 2018-07-12
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Plant Answer Line Question

Keywords: Cladrastis kentukea, Populus

I am trying to help my neighbors select trees for their front garden. The trees will be in a parking strip that doesn't have any structures near it or any overhead lines and it is on the north side of a fairly large 2-story house. We live in an old neighborhood with very large, grand trees. One tree I thought might be a contender, which is approved by the city (Portland, OR), is Cladastris kentukea. My only concern is that the seed pods might be messy. The neighbors themselves were thinking of aspen (nostalgic for them, as Coloradoans), but I didn't think this was a good idea. What do you think?


I checked in a few places, and the main thing that might be disappointing is that in the Pacific Northwest, Cladrastis kentukea doesn't flower reliably (although that solves the small trouble of seedpods, I guess!). Local tree expert Arthur Lee Jacobson says the following, in his book Trees of Seattle (2006):
"In nature this is an uncommon, even endangered species. It has been recorded to 87' x 23' x 96' wide, and has reliable bright yellow or even yellow-orange fall color. Its heartwood is also deep yellow. Uncommon in Seattle, Yellowwoods are unreliable as flowering trees: their white flowers appear full force in some Junes, but are absent or weak in most years. They have no other faults except a branching habit prone to breaking up; careful pruning can help with this."
(The Seattle-dwelling specimens of this tree which Jacobson lists are between 23-60 feet tall by 4 to 8 feet wide)

Below are links to information and images, from Oregon State University. This tree looks glorious when it flowers! Provided the spot is well-drained, and has no history of verticillium, to which Cladrastis is susceptible (see the link from SelecTree below for details), it seems like a great choice.

As an argument against aspen (Populus species, usually P. tremuloides in our area), Arthur Lee Jacobson mentions that they tend to sucker from the roots. The SelecTree site mentions twig and dry fruit litter, high allergen count, and numerous pest and disease problems.

Date 2017-08-15
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May 31 2018 13:14:08