How to Improve Your Soil

Soil is a complex material that includes all sorts of organic and inorganic matter. To support a healthy lawn, though, all soil has to do is:

When all these conditions are met, the soil will support not only a healthy crop of grass but also a number of beneficial microbes that improve the overall health of the soil.

To hold moisture properly, soil can’t contain too much clay or sand. Additives such as peat moss and compost will improve problem soil over time. But in the short term, the first step is to remove the thatch—the dead blades of grass that are compacted into a mat on top of the soil—and aerate the soil underneath. (For more information, see How to Dethatch Your Lawn.)

Grass needs nutrients to survive. These nutrients are present in soil that is rich in organic matter, such as decaying plants and animal waste. But in too many lawns, the soil itself is undernourished.

Light green or yellow grass is usually a good indicator of poor nutrition—usually too little nitrogen or iron. If your grass blades are yellow, take a soil sample to learn which soil amendments (additives) are needed. To deliver necessary nutrients, you must add fertilizer to the soil surface so that the grass can absorb some of it before the rain washes it away.

A pH test tells you your soil’s pH level—its acidity or alkalinity. If your soil is too acidic, in most cases you can add lime to raise the pH. If your soil is too alkaline, you can add sulfur to lower the pH. You can apply both of these ingredients in dry form with a lawn spreader.

Whether you’re adding lime or sulfur, you must spread it at the pounds-per-acre rate that the manufacturer specifies. If pounds per square feet is more a practical metric for you to use, you can simply convert as follows:

Plant roots can be very strong, as evidenced by broken sidewalks and cracked driveways that are ruined by spreading tree roots. Grass roots usually are very hardy, except in extremely hard soil with high clay content or in soil that has been overly compacted by machinery or heavy foot traffic.

To test your lawn’s root health, make a soil sample into a ball, then shake it gently once or twice. If it stays together, there’s too much clay. If it falls apart completely, there’s too much sand. If it breaks into loose clumps, it’s just right.

To improve root health, the best options are to aerate the soil with a power aerator and top-dress it every year with rich compost. Once the first few inches of soil are loose, the roots will grow deeper and provide more nutrients for the whole plant.

To aerate your lawn, use a power aerator—a simple walk-behind machine that looks like a rotary tiller. Its turning shaft has hollow steel fingers that dig into the soil (left) and pull out soil cores (right), leaving behind deep holes.