Lawn: fertilizing



Follow the 2010 law, use only what is needed, and avoid applications in early spring.

Phosphorus runoff from lawns can contribute to algae blooms and reduce levels of oxygen in water, killing fish.  The New York State 2010 Nutrient Runoff Law restricting the use of lawn fertilizer containing phosphorus is aimed at reducing the amount of phosphorus that makes its way to lakes and streams through runoff.

• Use of fertilizer containing phosphorus on non-agricultural lawns and turf is allowed only when a new lawn in being established or when a soil test indicates additional phosphorus is needed.

• Application of any fertilizer on non-agricultural lawns and turf is prohibited between December 1 and April 1. (November 1 to April 1 for Suffolk County, November 15 and April 1 for Nassau County, and other locales may have more restrictive laws.)

• Application of any fertilizer within 20 feet of a water body is restricted, and fertilizer spilled on impervious surfaces must be cleaned up.

• Retailers must display fertilizer that contains phosphorus separately from other fertilizers and must post signs notifying customers of the terms of the law.

With the new restrictions in mind, the following information can help you decide when and how much to fertilize.  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 to find out what you need.

A standard soil test allows you to monitor soil pH, phosphorus (P), potassium (K) and other nutrients, and recommendations for lime and fertilizers for lawns are developed from these tests.   Read more about soil testing at our testing resource page.

Unless a test indicates the soil is deficient, it is now against the law to apply a fertilizer that contains phosphorus to an established lawn.

More information on soil testing.


Nitrogen is key.

Nitrogen (N), represented by the first number on a bag of fertilizer, is the nutrient that drives turf performance.  It is also the nutrient most likely to be deficient.  Unfortunately, there is currently no reliable lab test that can relate some measure of soil N to lawn responses.  Until a reliable soil test for N becomes available, follow these guidelines:

• If you consider you lawn’s green-up, growth and thickness  acceptable, then do not fertilize.

• Avoid early spring applications except where turf is thin.

• The best time to apply nitrogen to cool-season grasses is when the grass is actively growing, in late-spring/early-summer and/or early fall.

• In most cases apply the rate recommended on the fertilizer bag. Most will suggest ¾ to 1 pound of nitrogen per 1,000 square feet.


What about lime?

Lawns thrive when the soil pH is in the 6.0-7.0 range. Lime can be added to the soil when a soil test indicates a pH<6.0. The best time to apply is when preparing the soil for planting so the lime can be mixed into the top 6 inches of the soil profile and has time to neutralize the soil. On established lawns use lower rates and water in so that the lime moves to the soil surface faster. A soil pH above 7.5 is less desirable. You may consider using acidifying materials like elemental sulfur or acidifying fertilizers to lower the pH. Never apply more than the recommended rate.  Check pH every few years to make sure it is in the preferred range.

More information on soil pH testing.


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 Kentucky 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.

• Older, established lawns often require less nitrogen than newer lawns, especially if clippings are returned.


Water it in.

If you can time the fertilizer application before a light rainfall, you can take it easy and let Mother Nature do the work. Otherwise, irrigate your lawn with a quarter to a half-inch of water after spreading fertilizer to get the material into the ground where it can be used by plants.


What you are likely to find at the garden center.

As with home lawn grass seed mixes, most big garden centers, big box stores and other retail outlets carry a similar supply of home lawn fertilizers.  The major distinction is between synthetic and natural organic fertilizer.

Most synthetic lawn fertilizers contain at least 40 percent 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, but can also leach from the soil.

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, so don’t expect a quick response during cooler times of the year.

Lawns grown on 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.


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 when loading spreaders. Sweep up spills before they become a pollution problem.


Compost: Too much phosphorus?

While compost can improve soils, many are high in phosphorus, difficult to apply at low rates and can wash off into water as easily as fertilizers. Depending on the source, compost additions may increase phosphorus levels far beyond what the grass needs and exceed levels considered a threat to water quality.