A quality lawn is only as good as its soil. And unlike a garden, it is difficult to see, feel and even work with the soil in a lawn. There are steps you can take to improve the soil in your lawn, but before you go putting shovel to earth, there are a few things to uncover about soil.
Soil consists mainly of mineral particles, along with air and organic matter. The three basic mineral particles in the soil are:
- Sand — Sand makes up the largest particles and adds more space between particles in the soil than the other two minerals. Soil that is 50% sand drains well, dries quickly and warms up faster due to better porosity. It also tends to be less fertile and more susceptible to moisture loss.
- Clay — The smallest particles (less than .0001-inch) in the soil are clay. Clay is the most dense, with the least water and pores between particles. A soil with 50% clay is the opposite of sand; it drains, dries and warms up slowly. It can be very fertile and has excellent water retention.
- Silt — Silt is a product of the weathering and decomposition of preexisting rock. It is between clay and sand in particle size. It behaves much like clay, but its larger particle size makes it faster to lose water.
Soil Texture & Structure
Soil texture is determined by the percentage of sand, clay and silt particles in your soil. How they are arranged and how big these proportions are dictates the nutrient availability and drainage of your lawn.
Soil structure refers to how these particles clump together, and is often influenced by organic materials in the soil. Think of it this way: At one extreme is beach sand, and at the other you have clay. At the beach, the sand particles are visible to the naked eye, water drips through it and very little grows. On the other hand, clay — which covers much of the U.S. — is slow to warm up and drain (it is clumpy and sticky when worked in your hand). Two very different textures and structures.
Clay soils need amendments to make them an ideal place to grow a quality lawn, or garden for that matter. The perfect soil is loam, which is somewhere in the middle. Loam is a mix of particle sizes and types, at about a 40 percent sand, 40 percent clay and 20 percent silt proportion. Loam soils hold water and nutrients while allowing excess water to properly drain.
There are simple methods you can take, such as testing your soil, to determine your soil texture and structure. We’ve outlined the steps in . Once you know the basic characteristics of your soil (sandy, clay or loam), then you’ll know what to do to improve it.
Soil pH: Acid or Alkaline?
Another factor of soil behavior is its pH, or the measure of the acidity or alkalinity of a substance. Many of the chemical reactions that occur in the soil rely on the pH. It is measured on a scale from 1 to 14, with 1 being extremely acidic and 14 being extremely alkaline. A pH of 7 is considered neutral. For example, vinegar has a pH of 3, distilled water a pH of 7 and baking soda a pH of 11.
For soil, the ideal pH range is between 6 and 7, or slightly acidic. This is important because some nutrients are only available to plants when the soil is within that pH range. Rainy areas, like the Pacific Northwest and eastern U.S., generally have low pH and more acidic soil. Soil can also be more acidic in certain areas of the lawn, particularly under and near evergreens, whose needles contribute acid properties to soil. is traditionally used to balance acidity. The soils of the Southwest and West have dry climates that lead to a more alkaline soil. These are often balanced by , but that is often a difficult task.
Testing your soil will give you an accurate read of the pH level. To properly test your soil, contact your county extension office. A soil test will provide exact information about the pH, as well as the texture of your soil, any nutrient deficiencies, and the presence of organic matter and harmful salts. A soil test report typically gives an analysis as well as recommendations for specific fertilizer, lime or sulfur amendments to create the ideal nutrient and pH levels.
Over time, fertilizing, mowing and foot traffic can cause a soil to become compacted, with far fewer pores for air and water. This means poor drainage and inadequate growth. An easy way to check on the compaction of your soil is to walk around your yard, pushing a metal rod into the ground. If it’s hard to get a 6 to 8 inch depth, your soil probably needs aeration. If it’s consistently resistant, you may have a “hardpan,” or severely compacted crust layer. Hardpan soils contribute to fungus and root rot, caused by poor drainage. Compacted soil should be aerated to introduce more porosity.
Within soil, plants, including lawns, require the basic nutrients supplied by fertilizers. They are:
- Nitrogen — makes plants grow and become green
- Phosphorus — promotes strong roots and stimulates seed development
- Potassium — for disease resistance and drought tolerance
- Iron, calcium, magnesium and other elements are also vital to soil’s overall health.
contain special Micronutrients to deliver a complete array of benefits for specific soil needs. Typically, lawns are fertilized with a higher percentage of nitrogen to promote green, healthy blades. Learn more about fertilizer and in our lawn basics section, or see our for a customized fertilization program. It tells you exactly which fertilizers to apply and when for your region and grass type.
Improving Soil Texture & Structure
Ideally, soil contains 5 to 10% of organic matter, which will get its makeup closer to the ideal, loamy soil. The organic matter in the soil whether inherent or introduced is eaten by microorganisms in soil, producing polysaccharides. These form humus, which allows clay and silt to form together into larger particles.
By creating bigger aggregates of particles, you create more openings for air and water to move through soil. That means better drainage, which gets more nutrients to plants and gives them room to grow and thrive.
Humus is essential in sandy soils, to capture moisture and nutrients that make a more fertile ground for growth. Luckily, it’s quite simple to improve the texture of your soil. Just adding organic matter, such as sphagnum peat, to the soil will improve nutrients, moisture and drainage. Turned into the soil, organic matter breaks up clay particles. In sandy soils, it binds the grains together and retains moisture and fertility.
Here’s a simple guideline for your soil:
- Sandy soils — apply 4 inches of top soil and work into the top 4-6 inches. Water will move more slowly, keeping nutrients available to plants and out of ground water. For best results, use .
- Heavy clay soils — these dense soils lack the proper consistency and aeration for good plant growth. Add 1-2 inches of topsoil, or Scotts Enriched Lawn Soil, and work into the top 4-6 inches of soil. Resist the temptation to add sand to clay soil to improve drainage. Unfortunately, it usually has the reverse effect, and leads to compaction due to the way clay and sand binds together.
- Average soils — even soils that roughly match a loamy profile can be improved by amendments.
At the very least, improving your lawn soil’s pH, aerating when needed, and making sure the soil contains the proper nutrients will ensure the success of your grass — as well as a greener, healthier lawn.