As spring progresses across Wisconsin, lawns are in various stages of greening up. Spring fertilization makes lawns greener, but having the absolute greenest lawn in spring is not necessarily better.

Nitrogen fertilization is a key component of home lawn care. Properly timed spring nitrogen applications play a key role in ensuring healthy lawns. Moderation is key; do not fertilize too much, too often, or too early. Overdoing it in spring can lead to top growth at the expense of root growth, which leads to troubles as the season progresses.

Start by choosing a quality nitrogen fertilizer. Terms such as controlled-release, slow-release, or slowly available nitrogen all refer to products releasing lesser amounts of nitrogen for plants to use over a longer period. This avoids undesirable surges of growth. Specific examples found in the guaranteed analysis section of fertilizer packages include sulfur-coated urea, polymer-coated urea, ureaform, or IBDU. Organic fertilizers often contain water-insoluble nitrogen (WIN), which is controlled-release. These quality fertilizers may be more expensive but have positive influences on lawn health.

How much to apply is the next major decision. A rate of about one pound of actual nitrogen per 1,000 square feet is suggested for spring. The higher the nitrogen percentage a fertilizer contains, the less product needed, and vice versa. Most product labels with spreader setting guides are calibrated for a one-pound rate. Dividing one hundred by the percent nitrogen in the bag (as a whole number) will tell you how much product is needed for every 1,000 square feet of lawn area to supply the suggested one-pound rate.

Finally, the decision of when is the proper timing for your spring lawn fertilizer application. May is the target month, exactly when depends on your location in Wisconsin. Earlier in the month in the south, later in the north. A good rule to help decide proper timing is wait until mowing your lawn twice and then fertilize.

Wisconsin law limits phosphorus application on lawns only to either newly established lawns or lawns where a soil test has shown phosphorus deficiency. Soil tests will determine phosphorus levels and if deficiencies exist. For this reason, lawn fertilizers sold in garden center outlets will have zero levels of phosphorus in them.

Research shows turfgrass is very efficient at holding nutrients in place and avoiding runoff issues, but fertilizers need to be uniformly applied directly to lawns. Use care when applying fertilizers, especially near ponds, lakes, and streams. Avoid having any material land off-target, including impervious surfaces, which can drain into storm drains and waterways.

Proper fertilizing gets lawns off to a great start for 2025. Make plans now!