What kind of ornamental trees grow well in clay?

Asked July 7, 2015, 1:42 PM EDT

What kind of ornamental trees grow well in our North Willamette Valley clay? We took out some red maples that weren't doing well (their roots were all coming back up to the surface) and the trees were in poor health as well. We re-landscaped with a rock garden (like a dry creek bed with drought-tolerant plants) but our homeowners association says we need to replace the trees. I believe that may be a problem since the new landscaping has a block wall edging the walk which I don't think will retain the root system of the maples. Can you suggest what may root in our hard clay and not crack our wall?

Clackamas County Oregon

1 Response

Almost all ornamental and shade trees grow beautifully in the Willamette valley. (In fact, at one point over 85% of all the shade trees planted in the USA and Canada started life in the Willamette valley, though California has since taken a much bigger percentage of the total.)

You mentioned that you took out red maples ea rlier because of tree roots on the surface as well as generally poor tree health. A few species of trees have many roots right at the surface, and some of these frequently develop large roots--University of Indiana lists Norway maple (Acer platanoides), red maple (Acer rubrum), sugar maple (Acer saccharum), ash (Fraxinus spp.), sweetgum (Liquidambar styraciflua), tuliptree (Liriodendron tulipifera), pin oak (Quercus palustris), poplars and cottonwoods (Populus spp.), willows (Salix spp.) and American elm (Ulmus americana) as examples of shallow rooted trees. However, very commonly large surface roots for these as well as many other trees is a result of frequent shallow watering. It is especially common when the only water trees get is from lawn sprinklers systems. Roots go where the water is, and if the only water is close to the surface, that is where the roots will grow. So, whatever trees you choose, do figure out some way to water them deeply (down 18 to 24 inches), though this can be substantially less frequently than the lawn requires.

By the way, our Willamette valley soils are often accused of being clay, because they feel like clay when they are wet and soggy; actually they are generally silty loams, rich in nutrients and and excellent for growing trees and other landscape plants, as well as all kinds of berries and many other food crops!

Here are two excellent resources for helping you select replacement trees. All should do very well here. Each list gives you specific information about height, spread, growth rate, and drought tolerance. When you see something interesting, do a Google image search to see what that tree will look like, both when young and as it develops.

Street trees approved by City of Portland

Suggested Pland Lists.... Trees