Clay Soil

Asked April 12, 2020, 2:07 PM EDT

Which type of amendment should I use to till into heavy clay soil for lawn reseeding? How much? How deep to till? What is the best type of amendment? Who has the best type for this kind of work in the Portland Beaverton area?

Washington County Oregon

3 Responses

Thank you for choosing Ask an Expert for help establishing a new lawn. Keep in mind that no matter the amendments you use to get the lawn going, your grass will have to deal with the soil you have eventually. Good, ongoing maintenance is the key to a good lawn.

Some type of organic matter is a general recommendation. Though too much tilling can damage the soil structure you need, it helps break up tight clay and provides soil microbes with the food they need to help out your root zone. For a 1,000 square foot lawn, you would till in up to 25 cubic feet of organic amendment, to a depth of about four inches. These amendments can be found at local nurseries or garden centers or a bulk suppliers.

To find soils sold in bulk near you, google/search “bulk soil Portland Oregon”. Contact your choice and talk with them about the soil amendment you need for your project. Most of our local suppliers are experienced in designing blends for home gardens and understand the needs of gardeners.

These Oregon Extension Service publications have excellent information on starting and maintaining lawns in our area.

Practical Lawn Preparation and Renovation. See here:

Practical Lawn Care for Western Oregon. See here:

Have a good gardening year,

Now that I tilled the compost in there are some areas that won’t break down completely so I can level and flatten the surface well, can I purchase something like a top soil to put over these areas or what do you recommend?

I’m also told I don’t won’t to use a sandy loam because I’m trying to amend a heavy clay soil and I don’t want to introduce sand to clay, is this correct?

To level a newly-tilled area, rake it level as well as you can. Rent or borrow a water roller. Once filled with water, these smooth the area and make uneven spots clear. Re-rake to fill the dips and flatten the bumps. Re-roll.

Sandy loam is available for mixing into existing soil. A sandy loam soil can have up to 20% clay in it, along with silt and sand particles. Just as a clay soil can have up to 40% sand in it. Problems come up when pure sand is added to a native soil high in clay. If you have to add material to bring up the soil level, just be sure to mix it in well with the existing. Layering one soil on top of another can lead to drainage difficulties.