Roxanne Zimmer is sending her grass to rehab.
Convinced that fertilizer and weed killers turn lawns into junkies that need chemical fixes to thrive, the Glen Head gardener and self-described environmentalist is in the midst of a bold experiment.
"This year, I'm going to go cold turkey: no fertilizer, and no watering," said Zimmer, a journalism professor at the College of New Rochelle. Instead, she aerated the soil, smoothed on rich compost, and stepped back to let nature do the rest.
Not many lawn-conscious Long Islanders would go that far. But in recent years, the local obsession with lush green turf has been tempered by a growing awareness that overuse of fertilizer and pesticides can contaminate groundwater and foul our bays. County and state officials are pushing lawn education campaigns, and have passed local legislation to promote safer turf care practices.
Experts say mastering a few basics -- when and how to mow, water and feed turf -- can help shrink your lawn's environmental footprint.
"We're going into a real big change in the industry at the moment," said H. Pat Voges of the Nassau Suffolk Landscape Gardeners' Association. In the past, "people were moving out from the city and they were just happy if we could make it green."
Contamination of groundwater by nitrogen from fertilizer and cesspools has long been a problem on Long Island, where drinking water comes from underground aquifers. Rain also deposits nitrogen oxides from exhaust and industrial emissions.
High nitrogen levels in drinking water can harm infants by decreasing red blood cells' ability to carry oxygen, leading in some cases to brain damage or death. Nitrogen that washes into rivers and bays may also trigger the growth of algae that sucks oxygen from water, leading to hypoxic "dead zones."
Less of a problem in Nassau, where sewer systems have diminished nitrogen inputs to groundwater, nitrogen contamination remains a concern in largely unsewered Suffolk. Pesticides have also been found there in shallow groundwater in agricultural and heavily landscaped areas such as golf courses.
Fertilizer is not the only source of nitrogen, but "it's significant enough to say you can't look the other way," said Stephen Jones, head of the Suffolk County Water Authority.
In the past year, two of the water supplier's 553 wells were temporarily taken offline because of nitrogen contamination. Raw water from 20 percent of the wells had levels that exceeded 5 parts per million (the state drinking water standard is 10 parts per million), while 11 percent tested positive for pesticides at levels equal to half the maximum contaminant level or greater. Raw water is tested, filtered and treated to conform with state health standards before it enters the drinking supply system.
ScottsMiracle-Gro, a leading seller of fertilizer, says lawn care products' role in water pollution has been overstated. Homeowners use less than 2 percent of all fertilizer and apply it an average of 1.7 times a year, said Chris Wible, the company's environmental stewardship director, citing its market research. "If used properly, fertilizer does not lead to contamination of groundwater."
But research by former Stony Brook University graduate student Jennie Munster found groundwater below fertilizer-treated turf sites in Suffolk had nitrogen levels that exceeded the state drinking water standard of 10 parts per million. "We followed the instructions on the fertilizer bag," said Munster, now a hydrogeologist in California.Lawns aren't inherently bad -- in fact, they have environmental pluses. Grass filters air pollutants, while root structure anchors soil and helps soak up rainfall, diminishing runoff.
Still, choices residents make about lawn care matter, said Ralph Tuthill, garden educator with the Cornell Cooperative Extension of Nassau County. Homeowners control about 75 percent of managed turf in New York State, according to an extension pamphlet. "Especially on Long Island, it's a very fragile thing," Tuthill said. "You have water on all sides," groundwater below, "and you have so many people that a little bit of pollution from each of them adds up."
Knowing what lies beneath is half the battle. You can buy soil test kits or take samples to your local Cooperative Extension for a small fee. Soil that's too acid or alkaline can stop plants from taking in nutrients no matter how much fertilizer you apply; limestone or other agents may help achieve the right balance. Soil testing will also indicate whether your lawn needs added phosphorus and potassium.
A thick layer of rich soil is crucial when installing a new lawn, said Thomas Kowalsick, a horticulture consultant with Cornell Cooperative Extension of Suffolk. "That's the time to get yourself some high quality compost or manure."
Nitrogen is the main nutrient that helps lawns grow thick and green. Most Long Island lawns probably need at least one application of fertilizer each year.
While homeowners often spread fertilizer early in the spring, Tuthill warns that can stimulate top growth at the expense of the roots. "The two best times are around Memorial Day and Labor Day," he said.
Some gardeners prefer organic fertilizer to chemical varieties. Cornell extension experts caution that both can leach nitrogen; slow-release fertilizer is a safer bet for groundwater than quick-release.
Suffolk County forbids fertilizer application during the cold months, when frozen soil and heavy rains increase the chances that nitrogen will leach into groundwater. Nassau is weighing a similar measure.
Cornell's mantra: mow high, mow often and leave the clippings. Keeping grass at least three inches long fosters sturdy root systems, limits weeds and reduces the need for extra fertilizer. Mow regularly, cutting no more than the top third to avoid stressing the grass.
Don't bag. Clippings on the lawn return nutrients to the grass and help build a layer of organic matter so you need less fertilizer.
Water deep, but less often, and do it early in the morning, when less evaporates. Watering too frequently or at night makes grass more susceptible to disease. Most lawns need no more than an inch of water per week. A tuna can by the sprinkler will serve as a rain gauge.
Diagnose the underlying problem. Thick, healthy lawns resist incursions better. Is your grass getting enough sunlight -- at least six hours?
Bare patches invite weeds; try reseeding before turning to weed killer. Apply spot treatments of herbicide instead of blanketing the lawn.
Timing is key. "A lot of broadleaf weed control is best done in the fall, you'll get much better results," Kowalsick said. "If your lawn is full of dandelions in the spring, you can kill them, but you really want to look at why your lawn got so infested."