Best Grass Seed for Clay Soils
We are in the process replacing the existing lawn at our residence. The soils are almost exclusively heavy, hard clay. The clay is almost impenetrable, even during the wet season. All shrubs and trees in excess of four inch diameter routinely fall over because their roots have not been able to penetrate the clay. We may ultimately have to resort to excavating the clay and replacing it with topsoil, then replanting the lawn over it. But for now, we have removed the existing lawn and replaced about 3 inches of sandy loam/fine compost mix on top. We have heard that tall fescues do well in clay soils, but will their deeper roots be able to withstand wet conditions in the winter, and rock hard conditions in the summer? Others have said that the only way to go is perennial rye grass. Is there an expert that can respond to our question? Much appreciated... Gary and Sue
Clackamas County Oregon
Thanks for your grass seed question. When asked about the best kind of grass for a new lawn, OSU turf specialist answers “I rarely give the same answer twice, because the best grass depends on the site, the owner and a dozen other variables.” He further states that there are several basic grass mixtures that cover most situations, that he describes in his publication Practical Lawn Establishment and Renovation (EC 1550) published by OSU Extension Service available online.
Of the basic soil structures, clay soil particles are the smallest and when dry the particles bond together in a solid form making it impenetrable as you have experienced. The remedy for clay soil is introducing organic matter, a step you have implemented and should continue. The nature of our wet weather seasons tends to break down essential organic materials (i.e. compost), so using best practices to maintain and increase organic matter into your landscape will also increase your lawn success.
Your 3 inches of sandy loam/fine compost mix a good beginning, next select a seed mixture based on the variables of your specific site and the continue with the establishment guidelines in Tom Cook’s publication.
Lawns in our region can be a challenge both in lawn establishment and lawn maintenance, so I suggest you also check out Doug Voderberg’s Practical Lawn Care for Western Oregon (EC 1521). Happy mowing!