There’s a saying that too much of a good thing is really bad, and in the case of phosphorous on lawns, the cliché rings true.
In Columbia, many residents unknowingly apply too much phosphorous (an ingredient in lawn fertilizer) to their lawns, according to John McCoy, watershed manager for the Columbia Association.
Over time, the phosphorous washes from residential lawns into Columbia’s man-made lakes, causing aquatic weed and algae overgrowth, which leads to poor water quality, according to McCoy.
“Wilde Lake is a good example,” said McCoy in an interview about the effect of phosphorous on Columbia’s lakes. “It has a good crop of phytoplankton. You should be able to see 3 feet or more down the water column, but you can only see a foot and a half.”
The lack of light penetration causes less plant growth on the lake bed and when algae dies off bacteria levels increase, according to McCoy. Less plant growth and more bacteria both decrease the amount of oxygen in the lake, leading to a less healthy ecosystem, according to McCoy.
In order to make sure you’re putting appropriate levels of fertilizer on your lawn, McCoy recommends you get your soil tested.
“If you’re applying anything to your lawn,” said McCoy, “you should know how much you need to apply, what you need to apply and you should be doing soil tests every three years.”
In April, the Columbia Association started a free program that allows residents to get lawn soil tested. Lawn sample bags are currently available at Village Centers. McCoy said that so far, 325 samples have been submitted for testing as part of the program.
“On average, soils in Columbia have sufficient phosphorous in them for a healthy lawn,” said McCoy. “Normally we recommend don’t apply phosphorous.”
The soil testing program was made available for free to residents through a grant received by the CA. The testing coincides with a 2011 Maryland fertilizer reduction act passed by the legislature, designed to improve the water quality of the Chesapeake Bay.
Many of the requirements of that act will go into effect in 2013, according to a summary on the Maryland Department of Agriculture website.
Beginning on Oct. 1, 2013, homeowners will be prohibited from applying fertilizer to sidewalks, driveways or other impervious surfaces; will be prohibited from fertilizing if heavy rain is predicted; and only applying phosphorous when soil tests indicate it’s necessary.
McCoy reiterated these points. He said not to apply fertilizer before a heavy rain, be careful when using spinning fertilizer spreaders to not throw it onto streets, sidewalks, driveways and avoid using too much fertilizer.
McCoy said that many home and garden centers have been stocking phosphorous-free fertilizer and he said residents should choose those if they’re going to fertilize.
“Our freshwater systems are phosphorous limited,” said McCoy. “At some point, our concern will turn to nitrogen (another cause of nutrient overload in freshwater systems), but we got a ways to go to reduce phosphorous.”
Next week, Patch will look at ways to manage stormwater on residential properties as part of our new series on Keeping Columbia’s Lakes Clean.