Regional Gardening Reports :: National Gardening Association

In the Garden:
July, 2011
Regional Report

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Adding natural phosphorous and nitrogen to the lawn is easy with grass clippings, decomposing leaves, compost.

Phosphorous- Free: Good for Lakes -- and Lawns?

Lawn care is in a revolution at its roots. Come autumn, we'll find fewer turf fertilizers with phosphorous (P). In 2012, the change will be watershed. Most commercially manufactured lawn care products will be absent phosphorous and have less nitrogen (N).

The handwriting is on the wall. States and communities are passing laws that regulate use of P and N on lawns and turf (golf courses). Virginia, Maryland, New Jersey, Minnesota, Florida, Washington, Wisconsin, Vermont (and communities in Canada) are legislating to dictate amounts, types, means, and times of application. Pennsylvania is considering regulation.

Here's to an environmentally sound shift to save our bays, rivers, oceans. P and N in runoff equals water pollution. Both have been used excessively, often unnecessarily for decades. The excess is carried downstream into water bodies, creating algal blooms and "dead zones" devoid of oxygen and, as consequence, fish and other aquatic life.

Manufacturers of consumer lawn and garden products are responding. Lance Latham, Scott's Miracle-Gro communications and environmental stewardship representative, said that Scott's is eliminating P in lawn care products except for starter fertilizer and organic products. Phosphorous isn't necessary for an established lawn but is "critically important" when starting a lawn, he explained

What About Our Lawns?
If you're already returning grass clippings to your yard, you're doing the right thing. Grass clippings contain phosphorous (P), explained Dr. Gary Felton, associate professor at the University of Maryland's Department of Environmental Science and Technology. Recycling grass clippings provides sufficient P to keep lawns healthy. Adding organic matter (OM), such as composted leaves, supplies even more.

"All plants need phosphorous," Felton said. "Turf, when it's healthy and growing, needs very little. But that's not zero. We often find .1 lbs. P for 1000 sq. ft. of soil is enough." Newly sown grass needs P for cell growth.

Old established lawns on good topsoil usually have more P than needed, Felton added. Enhanced by decades of 10-10-10 fertilizer application, they won't show any immediate or long-term effects from phosphorous-free lawn care products.

New lawns sown on nutrient-poor subsoil will need P. Legislation allows for that. Manufacturers are making appropriate lawn starter fertilizer mixes with P included.

Providing the P and OM the lawn really needs "makes the lawn healthier, improves soil tilth, and buffers the pH (keeps it from changing too fast)," Felton added. The ideal pH range for turf grass is 6 to 7.

Decomposing grass clippings also provide nitrogen. Felton returns his clippings, calculating they're worth about one pound of nitrogen per year. His is an old yard with established top soil and healthy fescue turf. He also applies slow-release, water-soluble nitrogen twice a year - two/thirds at 1 lb per 1000 sq. ft. in fall and another third in spring.

The formula is not one size fits all, he cautioned. Additional P and N will vary according with each lawn. "Fertilizing turf is environmentally beneficial," Felton advised. "If you don't fertilize turf, it's not a healthy plant. The benefits of grass go right out the door -- the cooling effect, generating oxygen, preventing soil and P erosion. Infiltration and anchoring the soil affect water quality. Thick, healthy turf crowds out crab grass."

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