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Florida Today: UF study: Rainy season fertilizer bans may harm your grass

Wednesday, February 20, 2013

Abstaining from fertilizing your yard during summer months — as Brevard County recommends — may harm your grass, according to Florida’s largest-ever study of turf grass and fertilizer use.

But environmentalists say what’s good for grass is bad for the Indian River Lagoon and other economically vital waters.

The findings announced Tuesday by University of Florida buck the logic behind local ordinances enacted statewide in recent years to ban rainy season fertilizer use. Brevard County stopped short of a ban but in December approved a recommendation that homeowners not use fertilizer between June 1 and Sept. 30.

UF’s findings could result in changes to a statewide “model” ordinance that Florida promotes as a way to reduce nitrogen and phosphorus runoff, the prime suspects in triggering massive fish-killing algae blooms.

“Many of the ordinances that have been put out there, on the surface, appear to be doing good things, but the science is suggesting it likely is not,” said Bryan Unruh, an associate professor of environmental horticulture at the University of Florida. “The unintended consequences of these ordinances is that you could have additional impairment.”

Unruh says the bans encourage excess fertilization prior to the rainy season, when the plants’ ability to use that fertilizer is considerably less. Grasses don’t grow much during cooler months.

Florida has more than 5 million acres of residential and commercial turf grass.

The Florida Department of EnvironmentalProtection funded the 8-year, $4.2 million study to judge the effectiveness of current state fertilizer recommendations, which have been in use about 13 years. Researchers with UF’s Institute of Food and Agricultural Sciences (UF/IFAS) conducted the study at facilities in the Panhandle, Gainesville and Fort Lauderdale, using turf grass soils and the management practices common to each area. Florida’s most popular turf, St. Augustine grass, was studied at all three sites.

They found:

Very small amounts of nutrients leach off lawns during summertime fertilizer applications, as long as the UF/IFAS recommended fertilizer rates are followed and the grass is healthy and growing

Nutrient leaching results from fertilizer application to dormant or unhealthy turf grass.

Newly laid sod should not be fertilized for 30 to 60 days because it will not have established roots for effective uptake of nutrients. The sod is likely to carry nutrients from fertilizer applications at the sod farm where it was grown.

Some environmentalists say focusing on what makes grass grow best misses an important part of the ecological equation.

“In ecosystems, we look at an entire nutrient budget,” said Leesa Souto, executive director of the Marine Resources Council, a nonprofit group based in Palm Bay that pushed for a rainy season fertilizer ban in Brevard.

“We’re not just talking about turf grass uptake efficiency,” Souto added. “The more nitrogen you put in, eventually the nitrogen’s going to come out.”

When it comes out in the lagoon, the nutrients can help trigger a chain of events that lead to harmful algae blooms. Those kill fish and seagrass — a crucial nursery habitat for fish.

“During the rainy season, when you’re grass is already growing faster than you want it to, you shouldn’t add fertilizer,” Souto said. “The question shouldn’t be about fertilizer uptake, it should be about fertilizer runoff.”

Homeowners should not automatically assume fertilizer is the cure-all for their lawn, IFAS officials said. Sometimes improper irrigation, light or mowing height are at play.

The best advice, IFAS officials say, is to follow the guidelines on the fertilizer bag or to consult local extension service agents. The general rule of thumb, according to IFAS, is to not apply any fertilizer before April or after late September, early October.

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