Fertilizing Your Lawn

Many home lawns are located near ponds, lakes, rivers and streams. These surface waters can be degraded by nutrient loss resulting from over application or improper application of fertilizers to home lawns. Groundwater can also be contaminated from nutrients lost from lawns. Recent research has provided data that should change the way we managing lawns.

New Recommendations for Managing Nitrogen (N) and Phosphorus (P) on Lawns

If an unfertilized lawn is considered acceptable, then do not fertilize.  If the lawn is considered unacceptable, assess why (pests, compaction, shade, low fertility, etc.).

If fertilization is deemed necessary:

¨ Do not apply N before spring green-up and apply no later than September 15th. Avoid fertilizing in the midsummer. 

¨ Apply one-half to one-third (or less) of that recommended N on the fertilizer bag label, then monitor lawn response. Reapply at the reduced rate only when lawn response starts to fall below acceptability.

¨ Slow-release N formulations are preferred over soluble, fast-release formulations.

¨ Apply a maximum of 2 lbs N/1000ft2/year on established lawns that are 10 years old or older. Newly seeded turf, especially on new home sites where the topsoil has been removed, may require more.

¨ If a soil test indicates that phosphorus (P) and/or potassium (K) are adequate, then fertilize with only nitrogen (N). If only blended fertilizers are available, choose the blend with the lowest P content.

¨ Avoid using P fertilizers on bare ground or low-density lawns, unless it is a new seeding.

¨ Never apply P fertilizer to saturated or frozen ground.

¨ Avoid applying P fertilizers when moderate to heavy rain is forecast.

¨ If near surface water (streams, rivers, lakes, estuaries, bays, coastal areas, vernal pools, wetlands or drainage areas), leave a buffer strip of at least 25 feet of unfertilized grasses or other vegetation around the water bodies.

¨ Avoid using combination products that include both fertilizers and weed killers. Fertilizers with herbicides many not be applied within 25 feet of surface water.

Other management considerations:

¨ Return clippings and mow as high as possible (leave at least 3 inches). This can supply slow-release nitrogen to the lawn and supply most of the phosphorus needs of the lawn.

¨ Choose grasses such as fescues that require less nutrient and water inputs.

¨ Maintain soil pH levels between 6.0 and 6.5.

¨ Consider seeding white clover or other low-growing legumes into the lawn to naturally provide nitrogen.

¨ If supplemental watering is applied, avoid overwatering. Do not exceed a total of 1-inch of water per week, including rainfall amounts.

Source: Wilson, L., J. Jemison, and L. Berg Stack: Making Recommendations for Lawn Fertilizer Application and Management, University of Maine Cooperative Extension March 2008.

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