gypsum or lime for heavy clay soil in West Salem

Asked July 11, 2016, 11:05 PM EDT

I live in the hills of West Salem. The builder of my subdivision "landscaped" by putting about 1 inch of topsoil on top of the heavy clay natural to the area, and then putting down sod. As a result, the grass roots only grow through the topsoil layer; they stop when they get to the clay, and the grass gets dry very quickly. It also requires a lot of fertilizer to stay green. My backyard, especially, is now mostly weeds. I have been wondering if putting lime or gypsum on it would help open up that clay and allow the plant roots to get into it. The soil test I did came out as about 7, surprisingly, so I don't want to put too much of anything on it. Thanks, Sarah Lingle

Polk County Oregon lawns and turf soil and fertility issues

1 Response

Hello Sarah:

With a pH of 7 you certainly do not want to add lime, which will simply increase the pH. I'm surprised that it is that high, it would be far more typical to see the pH around 6.0 or so. Did you have a lab test the soil, or was it a store-bought kit you used?
Gypsum will assist with development of soil structure, but only in so-called sodic soils characteristic of eastern Oregon. It is not the amendment of choice for soils in western Oregon. The best amendment for clay soil is organic matter, which as you can appreciate, is best incorporated prior to landscaping. If the landscape has failed to thrive and you are open to amending the soil, then excellent products for area-wide amendment such as yard debris compost are readily available at reasonable cost. Unfortunately your situation is far from unique: soil remaining after construction can have significant deficiencies, including compaction, which make landscaping very difficult indeed. There is more information on soil amendment in the OSU extension publication EC 1561, "Improving garden soils with organic matter". And feel free to contact me directly with further questions.

https://catalog.extension.oregonstate.edu/ec1561