How Compaction and Excess Thatch Ruin Your Lawn
The zone where grass meets soil is an amazing micro world of plant roots, bacteria, insects and complex chemical reactions. Healthy soil is soil that's loose enough to allow air, water and nutrients to pass into it to foster plant growth. Keep these concepts in mind:
Compacted soil strangles roots
The causes are many: In existing lawns, the top 1 to 1-1/2 in. of soil becomes compacted over time from foot traffic, riding lawn mowers, high clay content and rain. New lawns often have problems—beginning with home construction or remodeling—when topsoil is bulldozed, remixed with subsoil and over-compacted. Sod lawns that are hastily laid over unevenly graded lots look good enough for the contractors to get paid, but they can manifest problems after one or two growing seasons. In both cases, the eventual outcome is choked and starved grass roots.
Too much thatch chokes the lawn
Thatch is a tightly woven layer of partially decomposed grass roots and stems that can develop over several years in the zone between the crown of the grass and the soil surface. Contrary to myth, grass clippings don't contribute to thatch buildup, and power raking doesn't cure it. Thatch becomes a problem when it's thicker than 1/4 in. It's a sign that lawns have been over-watered at night, damaged by drought, over-fertilized with high nitrogen fertilizer or that the soil is too alkaline. Thatch occurs most often in new lawns when sod is installed over dips and voids in the regraded yard or in poor or improperly prepared soil and is then incorrectly watered. Break down excess thatch by using a rotary spreader loaded with thatch decomposter mix on the lawn (Photo 5).
You can reverse the damage
Revitalize compacted soils once a year. Run a power core aerator over the lawn to pull up plugs of dirt, creating voids in the subterranean soil to provide space for and stimulate new root growth (Figure A). The slashing action of the power rake's vertical tines slits the soil's surface where seed, nutrients and water can combine to regenerate the lawn.
America is serious about growing grass. Since the mid-'90s, the total acreage of lawns (homes, golf courses, businesses, etc.) has exceeded the amount of land used for agriculture. Soil types and grass varieties differ by climate and region. Learn more about your soils, grass varieties and recommended lawn care practices by talking with experts at garden centers or a county extension agent. For a more complete lawn assessment, take along two 4 x 4 x 4-in. lawn samples cut from the best and worst areas of your yard. The best time to aerate and reseed cool-season grasses (varieties like Kentucky bluegrass and perennial ryegrass) is four weeks before the trees lose their leaves in your area. The best time to rejuvenate warm-season grasses (varieties like zoysia grass, bermuda grass, tall fescue and St. Augustine) is late spring. If you follow this plan, you'll give your grass time to germinate, grow and recover from the aeration process before it goes dormant. You'll also be able to establish a fuller, thicker lawn to help keep next season's weed growth to a minimum.