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The Phosphorous-Free Lawn
by Charlotte Kidd, M. Ed. - posted 06/27/12

Several states now are regulating the use of phosphorous (the P in NPK) in general lawn care products. How will this affect your lawn? Here is what you need to know.



Leaving short grass clippings and dusting the lawn with shredded leaves to decompose provides enough nitrogen and phosphorous for established grass.

Lawn care is experiencing a revolution at its roots. And 2012 is a watershed year, literally and figuratively. Garden center shelves will have few if any turf fertilizers with phosphorous (the P in NPK). Most commercially manufactured lawn care products will be completely free of phosphorous. Others will have less nitrogen (N) too.

The handwriting is on the wall—literally. 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 exact amounts, types, means and times of application. Pennsylvania is considering regulation, too.

Phosphorous and nitrogen runoff has polluted our bays, rivers and oceans. These fertilizer components have been used excessively, often unnecessarily on lawns and turf for decades. The excess travels downstream into water bodies, creating algae blooms and “dead zones” devoid of oxygen, and as consequence, injures fish and other aquatic life.

On the Eastern Seaboard, the Chesapeake Bay has suffered significantly. Its advocate, the Chesapeake Bay Commission, formed in 1980, is a legislative group representing Maryland, Virginia and Pennsylvania. The commission provides research and other support to inform legislation on bay restoration. It’s now seeing the fruits of its labors. Watershed states recognize “turf” as their largest crop. They realize that minimizing runoff from lawns matters in preserving our waterways. They are legislating restrictions accordingly.

Industry Action

Manufacturers of consumer lawn and garden products are taking note. Lance Latham, Scotts Miracle-Gro communications and environmental stewardship representative, said that Scotts is eliminating phosphorous 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.

Lesser known and new companies are bringing different, more organically-oriented lawn care products to the market. For example, liquid and granular corn gluten is a sustainable nitrogen source as well as a pre-emergent used to control weeds by killing sprouting seeds.


Buying a combination of composted mushroom soil and quality top soil in bulk by the cubic
yard or scoop is one cost-effective approach to revitalizing large lawns.

Our Lawns Will Still Grow Well

This environmentally sound shift can benefit the Earth, our properties and our budget. If you’re returning grass clippings to your yard, you’re already 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 phosphorous to keep lawns healthy. Adding organic matter such as compost and composted leaves supplies microbial nutrients in small yet sufficient amounts.



Corn gluten is an example of a new lawn care product with no phosphorous and degradable nitrogen.


Lightly applied granulated garden manure is one type of beneficial organic material.


Mushroom compost is another source of organic matter that can be lightly applied.

“All plants need phosphorous,” Felton said. Phosphorous helps develop strong cell structure above and below ground. It makes the plant stiff so the blades stand up and roots are healthy. “Turf, when it’s healthy and growing, needs very little phosphorous. But that’s not zero—we often find 1 lbs. P for 1,000 sq. ft. of soil is enough.” Newly sown grass needs added phosphorous for cell growth.

Old established lawns on good topsoil have more phosphorous 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 phosphorous. Legislation allows for that. Manufacturers are making appropriate lawn starter mixes with phosphorous.

Providing the phosphorous and organic matter 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 1 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 ½ lbs. per 1,000 sq. ft. in fall and another third in spring.

The formula is not one-size-fits-all, he cautioned. Additional phosphorous and nitrogen will vary according with each lawn. He also applies a spring treatment of crabgrass inhibitor.

“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 erosion. Infiltration and anchoring the soil affect water quality. Thick, healthy turf crowds out crabgrass.”

For Felton, a healthy lawn is “one thick enough to inhibit weeds and control erosion, green but not emerald green. When I look down I don’t see any soil—only lots of grass blades and a few clippings. I don’t worry about finding weeds there now and then. Cutting it high, between 3 and 4 inches, keeps the grass healthy and takes care of a lot of weeds.”


(From State-by-State Gardening March/April 2012. Photography by Charlotte Kidd.)

 

 


Charlotte Kidd, M. Ed. is a writer, professional gardener, garden designer and garden coach. She’s a member of the Society of Environmental Journalists and the Garden Writers Association.