Bulletin #2154, Fertilizing a Home Lawn in Maine

By Laura Wilson, Assistant Scientist, University of Maine Cooperative Extension.

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Many Maine homes are near ponds, lakes, rivers, and coastal waters, or near ditches and storm drains that can carry pollutants to these waters. Even bodies of water that are miles away can be polluted by excess nutrients such as nitrogen (N) and phosphorus (P) found in common fertilizers we use on our home lawns. The threat of pollution is greatest when these fertilizers are over- or improperly applied. Groundwater can also be contaminated by lawn fertilizers that leach downward. Recent research has provided information that should change the way we choose to fertilize our lawns.

How to Use Fertilizers on Lawns

If your lawn looks healthy without fertilizers, do not fertilize. Many lawns don’t need fertilizer to perform well, especially if the lawn clippings are left in place to recycle nutrients.

If your lawn does not look healthy, determine the reason. Some causes might be soil compaction, shade, pests or low nutrient levels. If you need help to determine the problem, contact your UMaine Extension County Office.

If fertilization is deemed necessary, here are some things to consider:
- Test your soil before you fertilize to find out if some nutrients are lacking. Many Maine soils lack nitrogen but have plenty of phosphorus. Contact the Analytical Lab and Maine Soil Testing Service for more information, or pick up a soil test kit at your UMaine Extension County Office.
- Always fertilize with phosphorus-free fertilizer (look for “0” as the middle number in a fertilizer bag’s analysis), unless a soil test shows that your lawn needs phosphorus. If only blended fertilizers are available, use the formula with the lowest level of phosphorus.
- Check the bag’s label. Buy fertilizers that contain at least some nitrogen that is labeled “slow-release,” “slowly available” or “water insoluble.” These provide nitrogen for a longer period and reduce the likelihood of some nitrogen running off into surface water.
- Do not use products that include both fertilizers and weed killers. The application rates on the bag label are based on the weed killer rather than the fertilizer.
- If you are not basing your application on a soil test, then apply one-half to one-third (or less) of the amount recommended on the fertilizer bag label. Reapply at this reduced rate only if your lawn begins to look unhealthy again.
- Do your math! On older lawns, do not apply more than 2 pounds of nitrogen per 1000 square feet of lawn per year. New lawns may require more, especially at new home sites where the topsoil has been removed. Calculation instructions are below.
- Leave a strip of at least 25 feet of unfertilized grasses or other plants next to water bodies.
- Do not apply fertilizers before spring green-up or after September 15. Avoid fertilizing in midsummer. If fertilizing a Maine lawn once a year, the best time is around Labor Day. If splitting the fertilizer into two applications, the other application time should be in May, after spring green-up. If you choose to do one application, do not exceed one pound of nitrogen per 1000 square feet of lawn.
- Do not apply fertilizers just before moderate to heavy rain is expected.
- Do not use fertilizers on bare ground or sparse lawns, unless it is a new seeding.
- Never apply fertilizers to water-logged or frozen ground.

Calculating Nitrogen

For a healthy lawn use only what your lawn needs; no more than two pounds of nitrogen per year for 1000 square feet of lawn. It’s easy! Follow these five steps:

1. Measure the length and width of your lawn. Multiply these numbers to get the area (e.g. 30’ x 25’ = 750 square feet).

2. Next, multiply the area of your lawn by 0.002 (this gives the maximum amount of fertilizer recommended, which is a rate of 2 pounds nitrogen per 1000 square feet). Continuing this example, the amount of fertilizer recommended for 750 square feet would be 1.5 pounds of nitrogen per year (e.g. 750 × 0.002 = 1.5), but it is likely that even less is needed!

3. Now determine the amount of nitrogen in your fertilizer bag:

Locate the 3-number analysis on the bag; the first number is nitrogen (N). (e.g. a 10-0-1 fertilizer contains 10% N).
Divide the N number by 100 to get a decimal (10/100 = 0.10). Multiply this number by the weight of the bag to get the total pounds of nitrogen in the bag (e.g. a 40-pound bag of 10-0-1 fertilizer contains 40 x 0.10 = 4 pounds nitrogen).

4. To figure out the amount of the bag you should use, divide the amount of nitrogen needed for your lawn by the amount of nitrogen in the bag (in this example, 1.5/4 = 0.375 = about 1/3 of the entire bag).

5. This amount is all you need for the whole year. If you leave clippings on your lawn when you mow, divide this amount in half! Apply this reduced amount of fertilizer to your lawn around Labor Day (between August 15 and September 15), or split the amount and apply half in May, after spring green-up, and half around Labor Day.

Other Management Considerations

Mow as high as possible (leave at least 3 inches) and leave the clippings on your lawn. Your grass clippings act as a free and safe fertilizer; the clippings provide a source of slow-release nitrogen and adequate phosphorus for your lawn.
Consider seeding white clover into the lawn to naturally provide nitrogen.
When establishing a new lawn, choose grasses such as fescues that require less water and nutrients.
Avoid overwatering your lawn. Apply 1 inch of water per week, including rainfall. A simple rain gauge or small narrow container placed in your lawn can help you determine how much water your lawn is receiving. One thorough irrigation each week is better than several light sprinklings.
When using compost-based fertilizers, test soil every year for phosphorus to ensure that phosphorus levels do not become excessive.

VIDEO: How do I care for my lawn in an environmentally friendly way? (YouTube)

For more information, contact John Jemison, john.jemison@maine.edu, University of Maine Cooperative Extension, 207.581.2953 or 1.800.870.7270 (in-state).

Some of the fertilizer rate and timing information on this sheet is adapted from:

Guillard, K. 2008. New England Regional Nitrogen and Phosphorus Fertilizer and Associated.
Management Practice Recommendations for Lawns Based on Water Quality Considerations. University of Connecticut.

This material is based in part upon work supported by the Northeast States and Caribbean Islands Regional Water Program, under agreement number 2006-51130-03956. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

Call 800.287.0274 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

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