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Q.
Excessive rainfall, combined with an April fertilization by our lawn
care company, have the lawn needing mowed every four or five days.
While commenting on this situation to a neighbor, she told me that
you shouldn't fertilize a lawn until the first week of June, because
it helps moderate spring growth and reduces the incidence of lawn
disease. Does she know what she's talking about?
A.
Your neighbor is absolutely right. Rain alone can push that much
growth, and applying fertilizer in early spring only makes matters
worse. Besides, if you leave your clippings on the lawn, rather than
catching them, your lawn is already getting an application of slow
release nitrogen every time you mow.
The lush growth forced by excessive fertilization in early spring is
more susceptible to a number of diseases that occur in summer's heat
and humidity, including brown patch, leaf spot/melting out on
Kentucky bluegrass, and pythium. Although you can make fungicide
applications to manage these problems, attention to cultural
controls should always be the first the step in controlling lawn
diseases. That lush growth also will use more water when we do get
into hot, dry summer weather.
You do not mention when your lawn care company made the application,
but I imagine it was in conjunction with pre-emergence crabgrass
control, which would have been made in late March or early April.
Penn State's recommendations for a moderate home lawn fertilization
program call for one pound of nitrogen in late May or early June,
another pound in late August or early September, and another pound
in late fall, right around Thanksgiving. This last application
should be made after the grass has stopped actively growing but
before the ground freezes. Grasses put on significant root growth in
the fall, and this last application helps to support that growth.
Uneven fertilization produces "skunk stripes"
These are
general guidelines and are not a substitute for having your lawn's
soil tested every three years or so. Penn State soil tests examine
levels of phosphorous, potassium, calcium, magnesium, and soil pH
(acidity or alkalinity). Nitrogen recommendations are based on the
known needs of a given crop because it is very difficult to
accurately assess nitrogen levels in the soil. Nitrogen can be lost
to runoff, leaching and volatilization during hot weather, so the
soil's nitrogen content can change quickly.
It can be a little challenging for home gardeners to find a plain
crabgrass pre-emergence herbicide that is not applied in conjunction
with fertilizer, but it is available. These products include active
ingredients such as dithiopyr (Dimension), pendimethalin (Halts),
and prodiamine (Barricade). You will find the active ingredients
listed in small print on the lower left of the front of the bag.
Plain crabgrass pre-emergence herbicides will not have an analysis
displayed prominently on the bag. The analysis is the sequence of
three numbers found on any bag or container of fertilizer such as
10-10-10. These numbers signify the percentage of nitrogen,
phosphorus and potassium and are always listed in that order.
Organic gardeners who use corn gluten as a pre-emergence herbicide
will provide nitrogen too early, but because it depends on microbial
activity to break the corn gluten down into a form of nitrogen
plants are able to absorb, it should not produce an immediate flush
of available nitrogen.
MORE
Fertilizer facts
Lawn fertilization
Home gardening
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