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When to fertilize your lawn

Lawns don't need early spring fertilization

By: Sandy Feather 2008
Penn State Extension

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.

Fungicide applications for Lawns

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 lawn fertilization creates stripes in the lawn
Uneven fertilization creates a "skunk stripe" appearance due to the contrast between the grass that got more or less nitrogen fertilizer

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.

Crabgrass control

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.


fertilizer facts

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