LaGrange County Lakes Council
To promote, protect and preserve the quality of the lakes and watersheds of LaGrange County
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August 2004 Permission to reprint with attribution LaGrange County Lakes Council (http://www.lagrangecountylakescouncil.org/) The green lawns that ring a lake reduce run-off and erosion, produce oxygen, absorb noise and pollution, provide cooling and are the perfect spot for enjoying summer days. But the care and feeding of grass lawns is also a potential source of “feeding the lake” – and that’s not a good thing. One potential source of weeds and algae in a lake is nutrient run-off from the land. Excess nitrogen and phosphorus from lawn fertilizer promotes algae and weeds in the lake. The weed growth and death set up a cycle of eutrophication, or premature aging of the lake. As plants and weeds decay, oxygen levels in the lake decrease. Reduced oxygen levels may cause fish kills and eventually the lake fills with decayed plant and fish materials. Fertilizer Facts Fertilizer is usually a mix of nitrogen (N), phosphorus (P) and potassium (K). The composition of nitrogen, phosphorus and potassium (N-P-K) is expressed as a ratio on the package label. For example, a 4:3:2 fertilizer contains 4% nitrogen, 3% phosphorus and 2% potassium. Organic or inorganic fertilizer makes a difference. Organic fertilizer (or slow- or controlled-release) is better for your lawn (and ultimately, better for the lake) because it feeds the soil to feed the grass. It releases nutrients more slowly creating a long-term food source, which means fewer applications. Organic nitrogen fertilizer is usually applied just once per year, usually in the fall. Inorganic fertilizers (fast-release) are usually more concentrated and more soluble, can leach through the soil quickly and feed the grass directly (and possibly the lake). Nitrogen only, please; hold the phosphorus and potassium Nitrogen promotes rapid leaf growth and is the most important nutrient for healthy green, soft grass. Most lawns do not need the nutrients phosphorus and potassium. Don’t use a fertilizer with phosphorus or potassium without doing a soil test to see if these nutrients are required. If you’ve been using a fertilizer with these nutrients, your soil probably has a built-up residue. And it’s phosphorus in the lake (which may have come from your lawn) that stimulates algae blooms and weeds. Bottom line: use a nitrogen-only organic (or slow- or controlled-release) fertilizer and apply phosphorus and potassium only if indicated by a soil test. Lawn and fertilizer “Do’s” Do a soil test to learn what nutrients your soil needs to support a healthy lawn and plants. Do know the type of grass in your lawn and its nutrient requirements. Do use organic nitrogen-only fertilizer at a rate of no more than 1 lb. fertilizer per 1000 square feet. Do use a mulching mower to return grass clippings and nutrients to your lawn, reducing its need for fertilizer and saving you time and money. Do consider a buffer zone or filter strip to separate your lawn from the lake. This may include native grasses, blooming plants, shrubs, trees and aquatic plants such as cattails, rushes and lilies. Using native plants reduces shoreline erosion, provides habitat for fish and wildlife and lessens the chances of exotic species (e.g. loosestrife) invasion. Most importantly, native species can usually out-compete most weeds and do not need fertilizer because they are adapted to nutrient levels found in local soils. Do consider a modified “berm”, or slight hump in the ground, along the shoreline. This rise in the ground/lawn will serve as an obstacle to nutrient-rich runoff into the lake. Lawn and fertilizer “Don’ts” Don’t apply fertilizer more than three times per year. Don’t apply fertilizer to dormant or frozen lawns. Don’t apply more than 1lb. fertilizer/1000 sq. feet at one time. Don’t apply fertilizer, weed killer or other products within 20 feet of the lake. Don’t put leaves, grass clippings or limbs in the lake; this loads nutrients directly into the water (and feeds the weeds). Resources The Lagrange County Lakes Council website (http://www. lagrangecountylakescouncil.org) lists county and state offices with more information. The Minnesota Shoreland Management Resource Guide (http://www.shorelandmanagement.org) has great tips and resources. Great "Shoreland Management" article from the Summer 2004 Water Column newsletter, Clean Lakes Program, Indiana Dept. of Environmental Management.
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