Maryland has become the latest state to ban the use of phosphorus in lawn fertilizers and limit the concentration of nitrogen. Other states with similar laws include Michigan, Wisconsin, Florida, New York and New Jersey, and the list is growing. The aim is to protect water quality, since excess nutrients from lawn fertilization is a major source of pollution, but one that's difficult to control since it comes from so many different sources across the cities and suburbs of America.
While you might not think of your quarter acre as a source of pollution, grass -- spread out over countless patches of individually-owned yards -- is actually the largest crop in many parts of the country. In Maryland, for instance, there are 1.3 million acres of turf, according to Environment Maryland, and 1.5 million acres in other forms of agriculture; and those grassy acres are annually doused with an estimated 86 million pounds of fertilizer, much of which ultimately washes into the Chesapeake Bay. In communities that have enacted phosphorus bans, there have been relatively quick results in improved water quality.
Most, if not all, of these laws have exemptions for establishing new lawns, because phosphorus helps grass take root; and most, if not all, exempt organic fertilizers because they naturally contain small amounts of phosphorus. Most include provisions to enforce the law on commercial applicators, and not homeowners, but whether or not you're compelled by law to comply, you can learn about proper lawn maintenance from following the guidelines set out in the new rules.
To find out more about proper lawn fertilization, we talked to Paul Tukey, founder of SafeLawns.org, author of The Organic Lawn Care Manual ($13.50 at amazon.com) and a widely respected expert on organic lawn care. Here's what we learned:
Lawns Don't Need Phosphorus
With the exception of newly seeded lawns, established lawns rarely need phosphorus to grow. While it's an essential nutrient, it's not a limiting factor to growth, and it is typically replenished naturally, particularly if lawn clippings are left to decompose after mowing. While Tukey advocates organic fertilizers or better yet, homemade compost (see below), major synthetic fertilizer-makers are now providing phosphorus-free products. Scotts, for instance, will stop including phosphorus in all lawn fertilizers by the end of 2012.
Test Soil Before You Fertilize
Anytime the ground isn't frozen you can test your soil for its nutrient content, pH and organic matter composition. For a good sample, mix about a pint of soil, total, from four or five different areas of the lawn by digging a few inches down to where the roots feed. The most comprehensive test results will come from a local cooperative extension and may cost about $10. Before you consider adding a nitrogen fertilizer, or an amendment like limestone to change the pH, you want to make sure you're adding only what your lawn truly needs. (You can also buy at-home DIY soil test kits for as little as $0.35 per test at amazon.com or gardeners.com. Or, try this electronic soil tester ($18.95 at burpee.com.)
Fertilize at the Right Time of Year
If soil tests indicate fertilizing is necessary, you sill need to fertilize at the right time of year. In the northern third of the country, where grasses endure cold winters, fertilize in fall; energy stored in roots will provide all grass needs in spring. Elsewhere, fertilize in advance of the rainy season.
Avoid High-Nitrogen Fertilizers
If tests show your lawn need nitrogen, don't go overboard. More is not better. Tests have showed that two-thirds of high-nitrogen products run off or vaporize without affecting the grass, which is a waste of money in addition to being an environmental hazard. Plus, it's easy to burn your lawn with high-nitrogen fertilizers.
Time Fertilization with the Weather
Fertilizer applied in a drought is more likely to burn a lawn than to help it grow. Fertilizer and water are both necessary for photosynthesis, so without rain, fertilizer won't work properly. Check the weather, and fertilize only before the forecast calls for a steady light rain. Also, avoid fertilizing if the forecast calls for a strong thunderstorm, since your fertilizer will just run off into a local lake, river or bay. "Your dollar bills are just washing down the storm drain," Tukey said.
Spread Compost Anytime
Unlike commercial fertilizers (including organic fertilizers) compost tea can be applied at any time. Incidentally, compost is probably all most lawns need to grow well. "It's the only thing I've ever put on my lawn," Tukey said, "and the lawn is gorgeous."
Mow Properly to Get the Most Out of Fertilization
"Any of your best fertilizer intentions get blown out the window if you don't mow right," Tukey said. There are four major mowing rules, one of which has to do with watching the weather. If there isn't rain in the short-term forecast, then "put the damn lawnmower away." If you must mow during dry spells, trim only the smallest amount off the top.
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