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A. Martin Petrovic

A new law that aims to keep phosphorus in lawn fertilizers out of New York’s waterways went into effect January 1, 2012. But that doesn’t mean you can’t have a green lawn while preventing pollution of the state’s rivers, lakes and streams.

The main provisions of the law prohibit application of all lawn fertilizers from December 1 to April 1, and restrict application of lawn fertilizers that contain phosphorus to new plantings or when soil tests show that phosphorus is in short supply.

“It’s easy for consumers to comply with the law,” says A. Martin Petrovic, turf specialist in the Department of Horticulture, Cornell University. “Ninety percent of the turf soil samples that come to our lab have enough phosphorus to grow healthy grass. If you don’t need more phosphorus, you shouldn’t waste your money applying more.”

Phosphorus runoff from lawns can contribute to algae blooms and reduce levels of oxygen in water, killing fish, notes Petrovic, who has conducted extensive research on how lawn fertilizer moves in the environment. Phosphorus impairs more than 100 bodies of water in the state according to the New York State Department of Environmental Conservation.

But lawn fertilizers aren’t the only source of phosphorus pollution, Petrovic points out. Leaky septic systems, decomposing leaves, some road de-icing salts and runoff from farm fields and livestock operations also contribute to the problem. The law also prohibits sale of phosphorus-containing dishwasher detergent – another potent source.

Some commonsense provisions in the law will help keep fertilizers from directly polluting waters. One prohibits application to impervious surfaces such as sidewalks and roads, where fertilizer can quickly wash into storm drains and waterways, and requires immediate clean up of accidental spills. Another restricts applications near waterways. (See sidebar: How to keep lawn fertilizer out of our waterways.)

The law also requires retailers to display phosphorus-containing lawn fertilizers separately and post educational signs. County and municipal governments can enact more stringent lawn fertilizer regulations, and five have already.

Composts are exempted from the law. But Petrovic recommends using them with extreme caution. While compost can improve soils, many are high in phosphorus, difficult to apply at low rates and can wash off into water as easily as fertilizers.

If you think your lawn might be short on phosphorus, you’ll need to test the soil to document the need before applying fertilizer. But the law does not specify where or how soil should be sampled and tested, says Petrovic. One option he suggests is using Agro-One Services, a lab that works cooperatively with the Cornell Nutrient Analysis Laboratory and uses Cornell’s research-based fertilizer recommendations. (A phosphorus and pH analysis for turf soil samples costs $7. Visit www.dairyone.com/AgroOne or contact your local Cornell Cooperative Extension office for more information.) “We have the research to back up the recommendations they make based on the testing procedures they use,” says Petrovic.

Even if you don’t need any phosphorus, that doesn’t mean you should forego lawn fertilizer completely, he adds. It’s still important that lawns have enough nitrogen to thrive.

“If your grass doesn’t get sufficient nitrogen, your turf will grow thin, soil will be exposed and phosphorus losses will actually increase,” Petrovic points out. “You need a dense carpet of sod to minimize phosphorus runoff.”

Early-fall nitrogen applications encourage root growth and early green-up in spring. “People use nitrogen because they like the green,” notes Petrovic. “But more importantly, it’s for that thick growth you need to protect water.”

More information:

• Cornell Gardening lawn information [http://www.gardening.cornell.edu/lawn]
• Dishwasher Detergent and Nutrient Runoff Law (NYSDEC) [http://www.dec.ny.gov/chemical/67239.html]

Tips to help you be “green” and have a green lawn:

Mow high. Set your lawn mower at its highest setting. Taller grass encourages deeper rooting, better ground cover, fewer weeds and less phosphorus runoff than from lawns cropped too short.

Leave the clippings. That recycles nutrients and reduces fertilizer needs. “If your soil already has enough phosphorus and you return the clippings, you’ll probably never have to apply any more,” says Petrovic.

Mow leaves. Don’t rake them into the street (same with grass clippings) where they can wash into storm drains and waterways and contribute directly to phosphorus pollution. Shred them right where they fall on the lawn. (A mulching lawnmower works best.) Or if they are too thick for that, rake them into flower beds, around trees and shrubs or into compost piles.

Use care near water. The new law prohibits application of all lawn fertilizers within 20 feet of a waterway unless there is a 10-foot-wide vegetative buffer, or within 3 feet if you use a drop spreader or equip your rotary spreader with a guard or deflective shield that assures more accurate delivery.

Be careful with new seedings. While the law allows you to use phosphorus fertilizer on new seedings, Petrovic suggests testing the soil first, anyway. If levels are high, you might be able to skip the phosphorus, or at least wait until the grass comes up and the soil isn’t as vulnerable to erosion and fertilizer runoff.

Apply nitrogen as needed. But not before April 1. (It’s against the law.) Avoid early spring applications except where turf is thin. The best time to apply nitrogen to cool-season grasses is when the grass is actively growing in late-spring/early-summer and/or early fall. In most cases apply the rate recommended on the fertilizer bag. Most will suggest ¾ to 1 pound of nitrogen per 1,000 square feet.

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Cornell University turf specialist Frank Rossi explains how climate change will bring us fewer but stronger rainfalls, and how you can most efficiently water your lawn.

See also:

• Watering lawns at the Cornell Gardening Resources website.
• Lawn watering calculator from the Northeast Regional Climate Center

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Cornell University turf specialist Frank Rossi explains how proper mowing and fertilization can help you rein in crabgrass without herbicides.

For more tips on preventing weeds, see this free online publication: Lawn Care Without Pesticides.

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Cornell University turf specialist Frank Rossi provides simple tips for how you can reduce your lawn’s carbon footprint, such as raising your mower’s height to reduce how often you need to mow. Also see his previous podcast on reducing mowing.

Click link to listen to or download audio podcast.

Cornell University turf specialist Frank Rossi provides tips for how you can establish grasses that will look great with less mowing. Frank mentions these links in the podcast:

• Lawn information at Cornell Cornell Gardening Resources
• National Turfgrass Evaluation Program
• Seed Super Store