This is a Q&A blog series on healthy organic turf. If you have a question for Good Sweet Earth's lawn guy, Steve, shoot him an email at steve@GoodSweetEarth.com, and include "Ask the Lawn Guy" in the subject line.
Most people know what sandy soil and clay soil look like. They know that sandy soil is pretty loose and doesn't hold water very well. They know that clay soil can often feel hard and compacted. Most people also also know that nothing grows especially well in soil that's either of these two things.
Somewhere in between sand particles and clay particles lies silt. Loam soil contains a balance of all three types of particles.
So the question that I got recently was this: "How much sand should I add to my clay soil to loosen it up and make it usable?" And I suppose the counterpart to this question could be "How much clay should I add to sandy soil?"
In short, the answer is: Don't bother. You'll make your soil even worse by trying to change its structure with sand or clay.
Imagine your clay particles as marbles. Proportionally speaking, silt would be about the size of a basketball compared to those marbles. Now I had a hard time coming up with a real-world object that would be representative of a sand particle next to our marble-sized clay particle. The best I could come up with is this: Picture a ball slightly larger than a three-car garage. Yep. That's a sand particle next to a clay particle.
Now imagine you had a field full of marbles. And you want to "loosen" things up. I don't care how many three-car garages you add to that field of marbles, you're never, ever going to end up with a field full of basketballs. You're just gonna have a bunch of really small balls and really large balls, and they're not going to work together for anyone's good because you're never going to have enough garage-balls to balance the little marbles.
Ideally, healthy soil is equal parts marbles, basketballs and three-car garages. But getting that balance is so much harder than it sounds. I don't recommend attempting to change the mineral structure of your soil this way.
So what is a clay-burdened or sand-burdened gardener to do? Two words: Organic matter.
Clay-heavy soil has a very difficult time getting air through its tiny, tightly-bound particles. Roots also have a hard time moving through them. Organic matter, like compost or organic fertilizers, changes everything. This is the answer you seek, not sand. Mix that organic matter into your clay soil or top-dress it. Adding organic matter will make your clay soil usable in a way that adding sand never will.
Likewise, if you're dealing with sandy soil (an especially common problem if you live by the Lake Michigan lakeshore), adding organic matter will help your soil retain water and nutrients so much better.
Types of organic matter that you can add to your soil to make it healthier include basic compost (that many gardeners make in their own backyards), Worm Compost or Alfalfa Meal. Biochar (mixed with some sort of composted material) also makes for a terrific soil amendment.
For really compacted clay soil, gypsum is a good, natural option for de-compacting it before adding organic matter. For compacted lawns with clay soil, aeration is a good option, best done in the fall, followed by a top-dressing of organic matter and/or gypsum.
Steve & Corey Veldheer are organic yard & garden specialists in west Michigan.