University of Vermont
Fall News Article
Department of Plant and Soil Science
GROW HEALTHY LAWNS WITH LESS NITROGEN
Dr. Leonard Perry, Horticulture Professor
University of Vermont
Most know nitrogen is important for growth and good quality lawns, even if
just from watching television commercials. But if some nitrogen is
good, more is not necessarily better.
Nitrogen is one of the main fertilizer elements, the percent in a fertilizer
represented by the first number in the analysis. So a 5-3-4 fertilizer
would have 5 percent nitrogen. This element maintains dark green
color, enhances shoot density, and increases grass resistance to stress and
Too much nitrogen, however, can be detrimental to the turf grass. The
grass may grow too lush, and so have increased disease problems. Too
much nitrogen can reduce the lawn grass tolerance to high and low
temperature stress. And too much nitrogen increases growth
excessively, resulting in moisture stress and the potential for thatch (the
dense layer of intermingled roots and shoots, both living and dead, near the
soil surface that tends to block water and air).
Too much nitrogen also can be detrimental to the environment. Excess
nitrogen can increase the risk of ground water pollution. More growth
means more mowing. This means more time on the mower, more fuel used, and
more air pollution from the mower.
Since nitrogen moves readily into the soil with water (“leaches”), it
usually needs applying yearly in some form. There are some ways you
can reduce the amount applied, or applied as fertilizers, and so reduce the
risk of pollution.
-- Be willing to have good quality turfgrass that is green, but perhaps not
as dark green as the slick ads on television and in magazines. This is
possible by using less nitrogen fertilizer-- no more than one pound of
actual nitrogen per 1000 square feet per application, and no more than two
applications per year. So if using a fertilizer with 10 percent
nitrogen, you should use 10 pounds to get this amount of nitrogen.
-- Raise the mowing height to reduce turf stress and weeds. Many still
mow too low. Low mowing often is justified only on highly maintained
golf courses and similar situations.
-- Use specialty turf fertilizers that have a high proportion of water
insoluble nitrogen (WIN). When possible, use fertilizers with at least
50 percent WIN of total nitrogen. Natural organic sources are 100
percent slow release, which is desirable.
-- Apply fertilizer at appropriate times of year. Avoid or reduce
summer applications. The best once-a-year application is in late
summer or early fall.
-- Recycle grass clippings back into the lawns, such as with a mulching type
mower. About 46 to 59 percent of the applied nitrogen from fertilizer
ends up in the clippings. One estimate shows that returning grass
clippings can contribute about two pounds of nitrogen per 1000 square feet a
year. Returning grass clippings to the turf can reduce fertilizer
needs by 25 to 40 percent.
-- For some lawns, you may add or rely on a legume (such as white clover)
among the grass to add nitrogen. Legumes have bacteria on their roots
that take nitrogen from the atmosphere and convert it to nitrate forms that
plants can use.
Return to Perry's Perennial