By Susan McCabe, Colorado Master GardenerSM, Colorado State University Cooperative Extension, Denver
Does lawn care seem to be taking a lot more time and effort than it once did? Are the results less than you expected? Does the lawn contain those annoying brown spots that remain no matter how much you water, spray and fertilize?
If the answer to these questions is yes, it might be time to check on the health of the soil beneath your turf.
Healthy soil is teeming with life and activity. It's rich in organic matter, insects, earthworms, air, water and nutrients. Healthy soil is a must for thick, strong grass. What can you do to encourage a healthy soil in your lawn?
The simple answer is little, literally, except the usual watering, moderate fertilization, aeration and mowing. You might be killing your soil with kindness if you follow a strict multiple fertilizing, pre-emergent herbicide, insecticide, herbicide routine year after year. Your lawn could be "addicted" to pesticides and fertilizers because the natural balance of the turf ecosystem has been disrupted.
The turf grass ecosystem includes the roots, stems and leaves of the grass in addition to thatch, soil and pests. It also includes soil microorganisms, non-pest invertebrates, such as earthworms, spiders, beetles, oribatid mites, nematodes, annelids, ants and other arthropods that work the soil and are natural pest predators.
If this ecosystem is left alone, it will maintain relative stability. The thatch will be broken down and decomposed by microorganisms and earthworms. The pests will be held in check by predators, parasites, and natural plant resistance. In fact, excessive thatch build up and disease and insect damage rarely occur in lawn areas under minimal maintenance.
Studies show that even one application of a fungicide or insecticide at the recommended rate will reduce the earthworm population in the soil. In fact, many common insecticides and fungicides sold over the counter can kill 60 to 90 per cent of earthworms present. In addition, other beneficial insects and microorganisms also are adversely affected by pesticides.
Research examining sustained turf pesticide use over time shows increases in the number of pests because beneficial predators and competing microorganisms are killed. Pest resistance to the chemicals also has developed. While these pesticides can be useful in severe disease or insect outbreaks, they are best used as needed and as spot applications rather than being routinely broadcast over the lawn on a calendar basis. Even then, underlying stresses such as compaction need to be addressed to achieve real, long-term pest control.
In addition to pesticides, a lawn care program calling for high rates of nitrogen fertilizer will, over time, produce an excessive accumulation of thatch in the turf. The cause of thatch buildup is an imbalance between the production and breakdown of grass roots and stems at the soil surface. In lawns with more than three-quarters inch of thatch, water penetrates slowly, root growth is shallow and grass is more vulnerable to stress from heat and drought.
How can you develop a healthy, good-looking lawn free from chemical "dependence?" Concentrate on the idea that less is more. Help your soil's health through attention to mowing, watering, fertilizing and core aerating. Mowing means mowing regularly and mowing "high" - 2.5 to 3.5 inches. Allow the clippings to remain on the lawn; they naturally recycle fertilizer nutrients. Regular and proper amounts of water maintain healthy grass and other soil life. Moderate fertilizing provides nutrients to thicken turf and crowd out weeds. Core aeration relieves compacted soil and allows grass roots access to air for healthy growth.
Then, sit back and let the forces of nature do the rest of the work.
© CSU/Denver County Extension Master Gardener 2010
888 E. Iliff Avenue, Denver, CO 80210
Date last revised: 01/05/2010