St. Louis County urges caution with lawn chemicals to protect Lake Superior

Duluth-area yards can send fertilizer straight toward Lake Superior, and St. Louis County officials are warning homeowners that the mistake often starts with a routine spring application. The Minnesota Department of Agriculture and the St. Louis County Soil & Water Conservation District are urging residents to use lawn chemicals carefully because runoff from Duluth, Hermantown and nearby townships moves through a stormwater system regulated under the state’s municipal separate storm sewer permit.

That warning matters because the spillover is not just theoretical. St. Louis County says the Duluth and Hermantown area is part of an MS4 stormwater system overseen by the Minnesota Pollution Control Agency, which means what goes onto driveways, sidewalks and lawns can end up in local waters instead of soaking into the ground. Local conservation specialist Tryg Solberg has warned that urban runoff can carry excess fertilizer into lakes in a matter of hours.

The broader pollution problem is already well documented. A University of Minnesota study found that backyard chemicals such as fertilizers and pesticides are a significant source of nutrient pollution in Minnesota’s waters. In urban watershed research in Saint Paul, the university identified lawn fertilizers and pet waste as dominant sources of nitrogen and phosphorus in seven sub-watersheds of the Mississippi River, showing how household habits can scale up into a regional water-quality issue. For Lake Superior, that means the same spring cleanup that makes a yard look better can also feed algae and degrade water quality if it is handled carelessly.

Minnesota law has restricted phosphorus lawn fertilizer use since 2002. Under state guidance, phosphorus-free fertilizer is marked by a zero in the middle number on the bag. Phosphorus fertilizer is allowed only in limited cases, such as establishing a new lawn or when a soil test shows phosphorus is needed. When it is allowed, the Minnesota Department of Agriculture says it should be applied at rates recommended by the University of Minnesota and based on soil test results.

The practical mistakes are easy to spot and easy to stop: applying fertilizer before wind or rain, spreading it across pavement, using phosphorus products when they are not needed, and skipping a soil test altogether. The Minnesota Pollution Control Agency says reducing phosphorus pollution requires long-term strategies, and it also says Minnesotans can help protect lakes and streams by using less fertilizer and reducing runoff. In Duluth neighborhoods, that advice has a direct payoff: less waste in the yard, less pollution in the storm drain, and less strain on Lake Superior.