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Black out on nitrogen, phosphorous fertilizers in effect

By Staff | Jul 2, 2019

PHOTO PROVIDED A snowy egret forages in a cyanobacteria bloom caused by fertilizer runoff.

With the arrival of rainy season comes a black out period for certain fertilizers on Sanibel.

From July 1 through Sept. 30, a city ordinance prohibits the application of fertilizers containing nitrogen and phosphorous. However, products containing only secondary or micronutrients, such as magnesium and iron, may be applied throughout the black out period and are the sole exception.

“The goal is to reduce nutrient pollution to our local waters,” Holly Milbrandt, deputy director of Sanibel’s Natural Resources Department, said. “They (nitrogen and phosphorous) are the same two nutrients that cause algae blooms in local waterways. It all comes back to the water quality issue.”

She added that grass tends to grow just fine without fertilizer in the rainy season.

“So using it is sort of doing what Mother Nature is already doing by itself,” Milbrandt said.

She explained that the black out period only refers to fertilizer products that contain nitrogen and phosphorous. Called “summer blends,” there are products made with alternative components like iron, magnesium and potassium that fall under the exemption and are OK to use year-round on Sanibel.

“They benefit plants, do not impact water quality and can still be applied,” Milbrandt said.

Another point for property owners to be aware of is the black out rule applies year-round to areas within 25 feet of a body of water. Products containing nitrogen and phosphorous can never be used.

“Folks who might live on a canal or bay-front property owners,” she cited as examples. “Those adjacent to wetlands or the Sanibel River.”

The city’s ordinance stems from the challenge of trying to apply nitrogen and phosphorous in the summer when there are heavy amounts of rainfall. Milbrandt explained that the products can quickly get washed off into storm drains and local waterways, which puts more nutrients into the system.

“For us in the summertime, heavy rains are always imminent,” she said.

Milbrandt noted that similar black out periods are not uncommon for coastal municipalities. For example, Lee County has one in place that runs from June to September – one month more.

“Sanibel does not really get a whole lot of rain until July,” she said of what the city found.

Outside of the black out period – Oct. 1 to June 30 – there are rules that apply for those who use fertilizers containing nitrogen and phosphorous. The ordinance requires the use of slow release nitrogen and low phosphorus fertilizers. It also outlines the application usages permitted for the products.

Milbrandt explained that the products must have 20 percent or less of nitrogen, of which 50 percent must be slow release. In terms of phosphorus, the products must contain 2 percent or less of it.

“A lot of Florida soils are very high in phosphorus already,” she said.

As for application, the following rules apply:

– Up to one pound of nitrogen per 1,000 square feet per application.

– Up to four pounds of nitrogen per 1,000 square feet per year.

– Up to six applications per year.

“There’s sort of three parts to the application,” Milbrandt said.

The city recommends that property owners have their soil tested to better understand its composition and what is does and does not need. They can do so via the Lee County UF/IAS Extension Office.

Going fertilizer free is also an option.

Some tips for doing so include embracing native plants, planting the right plants in the right place, understanding how one’s landscape works – which areas get sun, which areas get water – and leaving grass clippings on the ground after it is mowed. Some also irrigate with the city’s reclaimed water.

“We know our reuse water has nitrogen and phosphorous in it,” she said.

For more information, visit www.mysanibel.com/Departments/Natural-Resources and click on the “Fertilizer Information Website” link. People can also call Natural Resources at 239-472-3700.