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Use only what you need, and avoid
spring applications.
Just like people, lawns need a balanced diet, too. If you feed them too much, too little or the wrong kind of fertilizer, they won't be healthy. With lawns, when you fertilize is critical, too. (Fall is better than spring.)
Test your soil. A soil test will tell you how much (if any) phosphorus (P) and potassium (K) fertilizer your lawn needs. Contact your local Cornell Cooperative Extension office or the Cornell Nutrient Analysis Laboratory for more information.
If tests indicate that no P or K is needed, use nitrogen fertilizer sources that contain little or no P and K.
Adjust pH, if needed. Lawns should have a slightly acid pH, between 6.0 and 7.0. If your soil tests fall outside of this range, follow instructions for adding lime or sulfur to bring pH into this range.
Focus on fall. If phosphorus and potassium levels are adequate in the soil, nitrogen (N) is the most important nutrient for grass growth. Understanding how grass grows is important when making decisions about how much and when to apply nitrogen fertilizer.
For most low-maintenance lawns, a single application in fall about two weeks after the last mowing is sufficient. Apply 1 pound of nitrogen per 1,000 square feet. (1 lb. N/1,000 ft.2). Use a fertilizer that is about 70 percent slow-release nitrogen.
For higher maintenance lawns, similar applications can be made around Labor Day and/or Memorial Day. But avoid early-spring applications. Research shows that these applications do not really enhance spring green-up compared with late-fall applications. (Neglected lawns or sods thinned by winterkill may benefit from .5 lb. N/1,000 ft.2 after the soil has thawed and drained but before the grass greens up.) At least 50 to 75 percent of the nitrogen applied to any lawn should come between the months of August and November.
Fertilizing healthy lawn in spring just increases topgrowth (and mowing chores) at the expense of root growth. This lush, succulent growth encouraged by spring fertilization makes the plant more susceptible to insects and diseases. Plants with smaller roots are also more vulnerable to drought later in the season.
Lawns that did not receive fall fertilizer applications or have suffered from winter injury may benefit from spring nitrogen applications. But wait until soil temperatures have warmed to at least 55 F before applying.
Water it in. Water your lawn with a quarter to a half inch after spreading fertilizer to get the material into the ground where it can be used by plants.
Consider the source. Most synthetic lawn fertilizers contain at least 40% slow-release nitrogen. Slow-release N becomes available to the plant over a period of time depending on soil moisture, temperature and microbial activity. The balance of the N is water soluble nitrogen, which is readily available for plant uptake.
In addition to supplying N over a longer period of time, slow-release nitrogen sources have a lower risk of burning plants and a lower potential to pollute water than water-soluble N sources. The tradeoff is that slow-release N is usually more expensive.
Natural organic fertilizers supply nitrogen in complex organic forms that are not immediately available to plants. They require warm, moist soils for microbial activity to release N. Natural organic fertilizers are well-suited for applications during warm summer months when the potential for burning plants with high-salt synthetic fertilizers is higher.
Lawns grown on mostly sandy soils should rely more on slow-release nitrogen to reduce the possibility of N leaching out of the root zone. Research shows that on most soils with some silt and clay, nitrogen leaching from lawns is a rare.
Consider different needs. High-traffic areas usually require more fertilizer than low-traffic areas. Different species of grass have different needs, too. Kentucky bluegrass, for example, requires more nitrogen than fine leaf fescues.
If bluegrass doesn't get enough N, it is less competitive against weeds and pests. If fine leaf fescues (which normally grow slowly) get too much N, they produce lush, weak growth that is susceptible to pests.
Apply with care. The whole idea is to get the right amount on the lawn and none in our streams and lakes. Rotary spreaders cover a wide swath. But they can also hurl fertilizer into streets and driveways where the next rain carries it into our waterways. A drop spreader may take a little longer, but it puts the fertilizer exactly where you want it. Use care loading spreaders. Sweep up spills before they become a pollution problem.
© Copyright, Department of Horticulture, Cornell University.
Website design: Craig Cramer cdc25@cornell.edu
Mention of trade names and commercial products is for educational purposes; no discrimination is intended and no endorsement by Cornell Cooperative Extension or Cornell University is implied. Pesticide recommendations are for informational purposes only and manufacturers' recommendations change. Read the manufacturers' instructions carefully before use. Cornell Cooperative Extension and Cornell University assumes no responsibility for the use of any pesticide or chemicals. Some of the links provided are not maintained by Cornell Cooperative Extension and Cornell University. Cornell Cooperative Extension and Cornell University are not responsible for information on these websites. They are included for information purposes only and no endorsement by Cornell Cooperative Extension or Cornell University is implied. Cornell Cooperative Extension provides equal program and employment opportunities.
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