Tips on Fertilizing Lawns

By Dawn Pettinelli, UConn Home & Garden Education Center

A healthy, vigorous lawn is the goal of numerous homeowners. That lush green lawn that is so often sought after is the result of the combined influences of a number of factors including good soil conditions, proper selection of turf grass species, correct mowing height, weed control, ideal soil pH range and adequate nutrition.

Just as a well-balance diet contributes to a person's overall health, a sufficient supply of nutrients is essential for strong turf growth. A frequent question we get from lawn growers is just how much fertilizer to apply and when to apply it.

The easiest way to answer this question, of course, is with a soil test. For a nominal fee, the University of Connecticut Soil Nutrient Analysis Lab (860) 486-4274 or www.soiltest.uconn.edu will let you know what your existing pH and nutrient levels are and how much, if any, limestone and fertilizer is needed for your lawn.

Without a soil test, a typical goal for Connecticut lawns is to apply 3 pounds of nitrogen per thousand square feet each year. Recent research at the University of Connecticut has demonstrated that if grass clippings are left on the lawn, they will decompose and supply about one-third of the nitrogen your lawn needs. So, if you are using a mulching mower then you would only need to apply 2 pounds of nitrogen per thousand square feet to your lawn each year. When applying fertilizer to established lawns, the recommendations typically call for no more than one pound of nitrogen per one thousand square feet to be put down in a single application. Any more and the turf grass plants will most likely be injured by the high nitrogen levels.

Most fertilizers, including those for lawns, contain the nutrients nitrogen, phosphorus and potassium because they are needed in large quantities by most crops and they are often deficient in our soils. Fertilizers containing all three of these nutrients, whether derived from natural or synthetic sources are referred to as complete fertilizers. The percentages by dry weight of each nutrient are listed on the package. So, for instance, a bag of lawn fertilizer with an analysis of 24-4-6 would contain 24 percent nitrogen, 4 percent phosphorus and 6 percent potassium.

A 100 pound bag for example would contain 24 percent or 24 lbs of nitrogen while a 50 pound bag of the above analysis would contain half that or 12 pounds of this element. You want to apply one pound of nitrogen on each 1000 square feet of lawn area in your yard so you need to determine how much fertilizer to buy. First you want to figure out how many pounds of 24-4-6 fertilizer would contain one pound of nitrogen. To do so divide the percent of nitrogen listed on the fertilizer package into 100 and you will get the number of pounds of that fertilizer than will provide one pound of nitrogen. So 100 divided by 24 equals about 4 so 4 pounds of 24-4-6 fertilizer would contain one pound of nitrogen.

Next you would need to estimate the approximate square footage of your lawn. If you lawn is 5000 square feet, then you would apply 5 times 4 pounds which would equal a 20 pound bag of 24-4-6. One would calculate the quantity of organic lawn fertilizers in the same way but do keep in mind that since they contain lower amounts of nutrients, greater quantities of fertilizer would be used to supply a similar amount of nitrogen.

Occasionally, the phosphorus or potassium levels in the soil are very low. A soil test might recommend using a garden fertilizer which is generally higher in phosphorus and potassium than those formulated for lawns for one or two applications. Another option would be use of a typical lawn fertilizer plus the one time addition of a source of phosphorus, like superphosphate, or potassium, like potash.

Ideal times to fertilize lawns are from mid April to mid June and then again in September through mid-October. Lawn fertilizers often contain nitrogen in both soluble (WSN) and slow release (water insoluble nitrogen or WIN) forms. Ideally, 50 percent of the nitrogen should be in slow release forms. This is almost always true when natural organic lawn fertilizers are used. Look at the label before purchasing the fertilizer. Do keep in mind that both natural organic and synthetic fertilizers if applied at high rates or at inappropriate times can contribute to ground and surface water pollution.

While fertility is an important component of any lawn management program, it will not make up for poor drainage, compaction, inadequate topsoil depth, shade or other site problems. These too will have to be addressed when striving for that really gorgeous lawn. If you have lawn care questions or other home or garden related queries, call the UConn Home & Garden Education Center (toll-free) at (877) 486-6271, visit www.ladybug.uconn.edu or get in touch with your local Cooperative Extension Center.   

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