Conservation Notes: Grass clipping and lawn fertilizer
Next time you’re out cutting the grass, pay attention to where the grass clippings are going. It’s true that grass clippings are a natural fertilizer when left on the lawn. In fact, returning clippings to the lawn surface for one full summer is equivalent to one application of store-bought fertilizer.
However, the same clippings can be problematic when they are blown onto a hard surface such as the street or driveway. Grass clippings and fallen leaves contain phosphorus. When they are blown onto a hard surface, grass clippings usually end up washing down the nearest storm drain and directly into a lake, stream, or river.
The phosphorus inside the grass clippings breaks down and is consumed by algae, which causes the green color of algal blooms on lakes. In fact, one bushel (about two 5-gallon pails) of grass clippings can contain 0.1 pounds of phosphorus, which can produce 30-50 pounds of algal growth in a nearby lake!
There are two simple steps that you can take to prevent grass clippings from reaching a nearby waterbody. First, pay attention to how you mow and make an effort to direct clippings back on to the lawn.
Second, when you finish mowing just take a few minutes to sweep up any stray clippings on your driveway or the street and return them to your lawn or a compost pile. It’s quick and easy, but it makes a big difference.
Also, if you use fertilizer on your lawn, follow these important instructions. Minnesota State Law states that you can only buy fertilizers without phosphorus (on the bag, make sure the middle number is 0, such as 10-0-10) to apply to established lawns.
Only use the recommended amount; more is not better. Plants can only use a certain amount and anything more than that is wasted. This excess washes off your lawn and makes its way to surface water, where it contributes to algae blooms and fish kills.
Never apply fertilizer over a hard surface like the sidewalk or driveway, and make sure fertilizer doesn’t spray into the street.
If it does, sweep up the fertilizer pellets and put them back on the lawn. If you live on a lake, avoid using fertilizer at all within 50 feet of the shoreline.