What is the most efficient and cost effective way to loosen clay soil under a typical "production home" lawn (little soil–lot of clay) in Northern IL? I've aerated 2 yrs now BY HAND—Spring/Fall—and although I prefer the deeper cores, it's getting harder to do every time. The "lawn care" guy told me to put gypsum and top soil down after wasting money for a service that didn't improve my lawn. I read on the UIUC ext. site that you don't recommend gypsum for IL soils since they tend to be calcium based. Pure Prairie Organics in Wheaton says we are magnesium based. What do I do? I put gypsum down last fall and last week. Can I get a definitive answer? I am tired of wasting money on fertilizing and watering when the problem is deeper.

Hi,

We often get this question about how to improve the structure of a soil after plants or in your case a lawn has been installed. It is not easy and often there is not a very efficient way of doing this because you don't want to start over. Ideally we like to see soil improvement done before planting and the best way is to incorporate a lot of organic matter into the soil. Many people think that gypsum is the magic cure for clay soils. While gypsum is often suggested to help loosen up clay soil by getting between the particles and helping to floculate or open up the soil for better air and ater movement it often takes time and if a plant is there again it can't be incorporated the way it should be. The only way I think you can help a tight clay soil under sod is to do vigorous core cultivation. This means using a machine that puts holes into the ground that are at least 4 inches deep and about 1/2 to 3/4 inch in diameter with the holes being no more than 2 inches apart. After that you can topdress with good soil that is worked into the holes and allows air and water to start moving down and supporting good root structure. Gypsum could be added but it isn't going to do the job as well as if it were to be fully incorporated. Doing this coring regularly will eventually start to "replace" the soil one core at a time allowing a better soil environment for root development.

sounds good, but what is "good" soil? and what is regularly(Spring and Fall? Or what?)

Spring and fall are both good times to core aerate. Fall if you are only going to do it once a year. Do this and top-dress while the sod is actively growing. The soil needs to be moist so the equipment penetrates the soil easily. A pulverized black dirt works, but even better is black dirt that is mixed with composts. Composts provide nutrition, water holding capacity and improve soil structure.