testing soil quality in a lab
Photo: Courtesy of Cornell Cooperative Extension
Is Your grass getting the nutrients it needs?
When soil lacks the essential elements for growth, grass becomes more vulnerable to disease, weeds, and pests. For about $20, you can get a soil test from your state's cooperative extension service, like the one at left. Some services will also explain how to correct deficiencies. Repeat the test every three years to keep up with any changes to the soil. Here are the most important categories the test covers.

pH
Determines whether roots can absorb minerals in soil. Ideal range for most grasses: 6–7. Add lime to raise soil pH; add sulfur to lower it.

Nitrogen (N)
Encourages blade growth. Most turf requires 3 to 4 pounds of nitrogen per 1,000 square feet each year but no more than 1 pound at a time.

Phosphorus (P)
Helps grass develop strong roots. Ideal range: 60–90 ppm. If low, add bone meal, dried seaweed, or fish emulsion.

Potassium (K)
Promotes growth and improves resistance to disease and drought. Ideal range: 70–100 ppm. If low, add granite dust or dried seaweed.

Calcium (Ca)
Builds strong cell walls and suppresses the growth of many weeds. Ideal level: 1,500 ppm. If low, add agricultural lime (not masonry lime) and wood ash, which also raises soil pH.

Magnesium (Mg)
Aids in chlorophyll production. Ideal level: 150 ppm. If low, add dolomitic lime.

Pro advice: Roger Cook, This Old House Landscape Contractor says, "When I seed a lawn I usually spread it at a slightly heavier dose, about one-third more than the bag suggests, to ensure I get a good stand of new grass.”
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