Summer Lawn Fertilization

With the often-used phrase of “timing is everything” in mind, early summer lawn fertilization is a key landscape management step.  In most lawns, turf is growing vigorously due to natural nitrogen mineralization and nutrient release after green-up in April, so there isn’t a great need to fertilize.  Once the spring growth surge subsides, an application will provide essential nutrients for the long summer ahead.

There are several considerations for summer applications of lawn fertilizer to cool season lawns such as Kentucky bluegrass and tall fescue:

First, as a homeowner, what are your expectations?  Lush lawn? Just something green?  Somewhere in-between?  The answer to this question will help you decide how much and what type of product to apply; higher amounts of fertilizer, particularly nitrogen, are required for high maintenance/high quality lawns.

Second, the age of the lawn.  Newer lawns (20 years old or less) need more fertilizer than older ones.  Mature lawns have had the benefit of years and years of organic matter deposits from trees (leaves, stems, fruits, flowers) and the lawn itself in the form of decaying roots and crowns to bolster the available nutrients.

Third, the current thickness, color and overall health of the lawn.  If a high-quality turf is desired and the turf is struggling, a slightly greater rate should be applied than if it’s already thick, dark green and relatively pest-free.

Fourth, the landscape setting for the lawn.  Lawns that are in poor health due to being sloped, in heavy shade, or receiving heavy traffic aren’t going to perk up simply from a shot of fertilizer.  Other limiting factors should be addressed separately, then the appropriate amount of fertilizer applied.

A blend of slow and quick release nitrogen should be applied.  Read the percentage of each indicated on the fertilizer product bag.  At least 25-40% of the nitrogen applied should be in a slow-release form.

In terms of how much should be applied, the general range of a half to 3/4ths of a pound of actual nitrogen per 1,000 sq. ft is a good guideline for early summer.  This is important to note since all fertilizer products are designed to provide a full pound of nitrogen if the recommended spreader settings are used.

The amount of fertilizer to apply can be easily calculated.  Simply divide the pounds of nitrogen per 1,000 sq. ft. desired by the first number in the fertilizer analysis expressed as a percentage.  The result of this calculation provides the amount of fertilizer product to apply over 1,000 sq. ft. of lawn.  For example, if you’re interested in a half pound of nitrogen per thousand square feet, using a 28-2-4 fertilizer product, divide 0.5 by 0.28, which indicates that 1.8 pounds of product should be applied.  Next, simply multiply 1.8 by the number of 1,000 sq. ft. units in the lawn, such as 5 for a 5,000 sq. ft. lawn…which is 9 pounds of product in this case.

After application, water the lawn lightly to wash the fertilizer granules off the grass blades and into the upper layer of soil.  This will prevent fertilizer burn and activate the product.

Early summer is also a good time to fertilize warm season lawns such as zoysia and buffalograss.  Since zoysia and buffalograss are low nitrogen users, a quarter to half pound of nitrogen per 1,000 sq. ft. should be applied.

John Fech
Horticulture Extension Educator at Nebraska Extension
John Fech is a horticulturist with the University of Nebraska-Lincoln and certified arborist with the International Society of Arboriculture. The author of 2 books and over 200 popular and trade journal articles, he focuses his time on teaching effective landscape maintenance techniques, water conservation, diagnosing turf and ornamental problems and encouraging effective bilingual communication in the green industry. He works extensively with the media to extend the message of landscape sustainability, making over 100 television and radio appearances each year.
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