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Village of Sussex, WI

Fertilizers & Wisconsin Lakes...Why is the Lake Green this Year?

  • Don’t Feed the Aquatic Plants and Algae
  • Why are Soil Tests Important?
  • How Much Fertilizer Should I Buy?
  • When and How to Apply Fertilizer
  • What do the Numbers on the Bag of Fertilizer Mean?
  • What to do with Spilled Fertilizer
  • When to Water
  • Where Can You Obtain Phosphorus-Free Fertilizer?

Don’t Feed the Aquatic Plants and Algae
Fertilizers contain nutrients (phosphorus, nitrogen and potash) which feed plants. The nutrients, especially phosphorus, feed the plants that grow in lakes. When you fertilize your lawn it is important to know exactly what the nutrient needs of your lawn are. If excessive amounts of fertilizer are applied you are fertilizing the aquatic plants in lakes and streams near your community.

If you feel that you must fertilize consider using non-phosphorus. Studies have shown that lawns rarely need phosphorus.

If it is necessary to fertilize to maintain a ground cover in order to prevent erosion try using small amounts of nitrogen fertilizer. The idea is to have the grass use the nitrogen so it will remain vigorous and minimize the amount of un dissolved fertilizer on the lawn surface capable of washing into the lake.

Why are Soil Tests Important?
The most economic and ecologically sound method of knowing if your lawn needs fertilization is to have a soil test run. A soil test will tell you if you need to fertilize, what type of fertilizer to use and the amount your lawn needs. This test can save you money and time. More importantly, it will keep fertilizer out of lakes and streams where they simply add to excess aquatic plants and algae. These aquatic plants and algae reduce the recreational and aesthetic values of our lakes and streams. DON’T FEED THE AQUATIC PLANTS AND ALGAE IN YOUR LAKE . For more information on how and where to bring your soil sample contact your local county extension office. They will send you instructions and methods for sampling lawns. Extension agents can also assist you in interpreting the results of the tests.

How Much Fertilizer Should I Buy?
The soil test will tell you how much fertilizer of a certain type to buy per square foot of lawn. This rate multiplied by the number of square feet you plan on fertilizing will tell you how much to buy. Buy only as much as you need.

When and how to apply fertilizer
The best time to apply fertilizer is in the spring and early fall when grasses are actively growing. Use a spreader that can be calibrated. A calibrated spreader will ensure uniform distribution of fertilizer and helps prevent over use. Fertilizer should not be applied when the grass is wet and during times of high winds an/or heavy rains.

What do the Numbers on the Bag of Fertilizer Mean?
The numbers on a bag of fertilizer refer to the percentages of plant nutrients nitrogen, phosphorus, and potash in the material. In a 100 pound bag of 5-10-10 mixture for instance, there would be 5 percent or 5 pounds of nitrogen, 10 percent or 10 pounds of phosphorus as P2O5, and 10 percent or 10 pounds of potash (K2O).

What to do with Spilled Fertilizer
Sweep up any fertilizer you may spill on hard surfaces. Any fertilizer left on blacktop or concrete will be carried, with the first rainfall, into lakes or streams.

When to Water
Water the lawn after applying the fertilizer just enough to wash the fertilizer off the grass leaves and into the soil in order to eliminate any possible danger of salt burn and to make sure the fertilizer gets into the soil where it’s needed.

Where Can You Obtain Phosphorus-Free Fertilizer?
Check with your local nurseries for their sources. Farmer’s cooperatives can blend whatever you would like, but may require that you purchase in bulk. Work with neighboring property owners or your county extension agent to find a cooperative that can handle your request. Ordering the fertilizer as a lake association or district should also be considered.

Lake Management Program
Wisconsin Department of Natural Resources
University of Wisconsin-Extension , UWSP

Sussex Civic Center

N64 W23760 Main Street