How Many Inches of Topsoil Do I Want for Grass?

Topsoil comprises most of the dirt action — it is where organic matter decays and beneficial microbes dwell. This creates a healthy atmosphere for grass roots to prosper over the less busy but often mineral-rich subsoil. When starting a new lawn, you can use your existing topsoil if the top 4 to 6 inches are rich with the organic matter that supplies nutrients and drainage, or you’ll be able to purchase a better quality topsoil if your garden soil is heavy clay or too sandy. Adding and preparing the topsoil properly can help establish a healthy, problem-free lawn.

The origin of the problem

The subsoil beneath the loose, nutrient-rich layer of topsoil doesn’t usually hold moisture or nutrients well. It may suffer from poor aeration, which prevents the roots from obtaining oxygen, or it may be heavy in stone, clay or salts that could damage or slow bud development. Grass only sets down superficial roots in a thin a layer of topsoil, which could lead to thin growth and nutrient deficiencies. It can also also make the lawn more susceptible to drought stress or need more frequent watering. Grass roots grow between 4 and 6 inches long, so a layer of topsoil that is 6 inches deep supplies enough space for the roots to grow.

Minimum Requirements

High-quality topsoil should feel slightly gritty when you rub it between your fingers, which suggests mineral content, while being dark to almost black in colour, which signals the soil is also rich in organic matter. Poor topsoil may feel and appear sandy, or it may have deep clay particles that induce it to clump and harden as it dries. The layer beneath the topsoil, called the subsoil, doesn’t usually contain as much organic matter and typically is not as high quality as topsoil, often being more rocky or sandy compared to the desirable dirt on top. If you have poor topsoil, you can buy topsoil so your lawn has a better prospect of growing well.

Work With It In

Placing topsoil straight on top of this subsoil produces a drainage issue. Prior to putting the topsoil, until the top two to three inches of the subsoil to loosen it, and level the lawn surface. Grading means leveling the lawn area to eliminate any low spots while sloping the lawn gently away from buildings and driveways. Apply the topsoil within a 4- to 6-inch layer and then until it to the loosened subsoil. This gives the grass a deeper rooting zone, while the more slow change to the indigenous subsoil allows water to drain and soak more deeply to the ground. If the lawn has reduced places, fill them using topsoil before inserting the regular 4- to 6-inch layer on top so the whole lawn has a level, gentle slope. After applying the topsoil, rake to grade the lawn again so it’s level and ready for seeding.

Some Improvements

Your garden soil may want the boost of additional organic matter, which you can supply by blending it with a 1- to 3-inch layer of compost. Clay topsoil is hefty and can impede drainage, while sandy topsoil drains too quickly and doesn’t support nutrients well. Mix the compost to the top 4 to 6 inches of existing topsoil. If you bring in fresh topsoil, add the compost in addition to putting it above the lawn area, and then until the compost and the topsoil to the top 2-3 inches of subsoil.

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