Growing a Great Lawn in Clayey Soil

November 7, 2020

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Growing a Great Lawn in Clayey Soil

Growing a lawn in clayey soil can seem like an insurmountable challenge. The dense, hard soil can be difficult to work with and poorly suited to growing pretty much anything. But clayey soil is both a curse and a blessing. No one would dispute that growing a great lawn in clayey soil takes some extra work, but there are benefits, too. Clay is often incredibly fertile, and with the right amendments can grow a thriving lawn. The small, compact particles of clayey soil also home water so that a lawn in clayey soil may need less frequent irrigation. If your soil is clayey, don’t despair. We can help you grow a great lawn even in clayey soil.

Growing a Great Lawn in Clayey Soil [infographic]

Step 1 – Test the Clayey Soil

The first step in any major adjustment of your soil should always be testing. You many have a pretty good idea that your soil is dense and clayey. But there is a lot of variety within clayey soil, including the pH, nutrient levels, and proportion of organic matter. Trying to amend your soil without knowing where you’re starting would be like trying to repair a stalled car without looking under the hood.

The best place to test your soil is at your local county extension office. These offices are staffed with experts who can answer your questions about all sorts of cultivation, including your turfgrass. And they often offer comprehensive soil testing for a small fee. Many garden stores sell at-home testing kits, but an extension office will do a more thorough test, and the results usually include recommendations to improve your soil.

Take a fresh soil sample to your local extension office earlier in the week, so that there is time for the sample to be sent to a lab and returned before the weekend. Armed with your results, you can now begin to amend and improve your clayey soil.

Step 2 – Adding Organic Matter

One of the most common amendments for clayey soil is simply to add organic matter. However, it’s not a one-time cure-all. Instead, clayey soils need to be worked and reworked over time, gradually adding more organic matter to reach optimal levels.

To get an idea of why you can’t introduce all the organic matter your soil needs in a single treatment, consider these numbers:

  • The average residential lawn is .25 acres, though in many parts of the country they can be much larger.
  • 6 inches of topsoil—the depth sampled in most soil tests—over .25 acres weights about a half-million (500,000) pounds
  • The average level of organic matter in untreated soil is about 2%. In .25 acres of topsoil, that’s about 10,000 pounds of organic matter.
  • Most experts agree that fertile soil should have 3% to 5% organic material.
  • To increase the level of organic matter from 2% to 3% you would have to add 5,000 pounds of organic matter.

Adding 5,000 pounds of organic matter would mean 250 forty-pound bags of topsoil, although even those bags are not 100% organic matter. So you can see that you can’t just amend your way to perfect soil in a single application. Instead, it takes multiple applications over months and years to achieve optimal soil composition.

Adding Organic Matter Before Sod

If you haven’t laid down your sod yet, you are in luck. This is a great time to begin adding organic matter to your clayey soil. When a home is built, builders often dump excess dirt—for example, from digging a basement—onto the rest of the property. The dirt, often dense clay, covers up the fertile topsoil, making it difficult to lay down sod after the home is built.

If that’s the situation you find yourself in, you can start by laying two to three inches of organic matter over your future lawn and tilling it under. To spread the organic matter, your best bet is a simple wheelbarrow and a shovel. Use the shovel to spread the organic matter as evenly as possible. You can add a little extra if there are dips in the soil to create a flat, even surface for your sod.  To till it under, you’ll need a rototiller, which you can usually rent at a garden store. Once the soil is prepared this way, you can lay down fresh sod.

Adding Organic Matter to an Established Lawn

If you already have an established lawn, you can’t just add organic matter and till the soil. That would rip up your turf. So the only option is to add a topdressing of high0quality hummus or organic material and wait for it to settle into the clay. Since you are not actively incorporating the organic matter into the clayey soil, you will need to repeat this step multiple times. To help the new topsoil mix with the clayey soil, use the backside of a rake to gently brush the hummus into the soil without disturbing the turfgrass.

Step 3 – Aerate the Clayey Soil

If you have an established lawn that can’t be tilled, the next best option to aerate your lawn before applying the topdressing. Use a core aerator—it will pull up plugs of clay about ¾-inch in diameter and 3 inches long. You can rent a core aerator at most garden stores. Make sure to go over your entire lawn at least twice to get the full benefit of aerating. The holes left behind allow water, nutrients, air, and your added topsoil to reach further into the grand toward the grass roots.

Step 4 – Take Care of Drainage

Even after adding top soil or tilling the ground, clayey soil doesn’t absorb water as well as loamy soil. To deal with that reality, you will need to plan on some effective drainage. You can use french drains or simply grade your lawn to drain into a nearby ditch or storm drain. Just remember that if the water is ultimately headed for a storm drain it is crucial that you don’t overfertilize. Fertilizer, just like water, will have a harder time penetrating clayey soil, so it is more apt to become runoff. Fertilizer that enters a storm drain and gets into local waterways is considered pollution and can cause algae blooms and other problems that can seriously damage the fragile ecosystem of the waterways.

When you’re dealing with clayey soil, it is crucial that you start with a high-quality turfgrass. Laying down the best sod is the only way to ensure a green, healthy lawn even under non-ideal circumstances. You can learn more about our certified turf varieties on their individual pages, or find a grower in your area here.

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