Avoid Early Spring Lawn Fertilizing - U of I Extension

News Release

Avoid Early Spring Lawn Fertilizing

This article was originally published on February 10, 2010 and expired on March 15, 2010. It is provided here for archival purposes and may contain dated information.

Fertilizing lawns in the early spring may not be best for the grass in the long run, according to David Robson, University of Illinois Extension horticulture educator, Springfield Center.

Unfortunately, advertising and chemical combinations in the spring makes it next to impossible not to apply some form of plant food. The concept of "keeping up with the Jones" and their nice, lush green lawns also drives us to the fertilizer bag and lawn spreader.

Most Illinois lawns are composed of cool season grasses such as Kentucky bluegrass, turf-type tall fescue and perennial ryegrass. Shady areas may contain additionally creeping, red or chewings fescue. These grasses remain actively growing as long as temperatures are lower than 85 degrees Fahrenheit.

Studies indicate grass roots are actively growing when temperatures are between 55 and 65 F. Grass shoots start developing when temperatures range between 60 and 75 F.

Grass roots are the first to start thriving when spring temperatures warm. New and deeper roots are formed, creating a network of interlocking roots. The deeper the roots, the more likely the grass plant will be able to survive hot, dry summer conditions. The emphasis is on "dry."

So, our spring lawn care goal should be aimed more at developing a deeper and more extensive root system than encouraging green thick shoot growth.

Unfortunately, nitrogen fertilizer promotes shoot growth at the expense of the root system. Even with cool soil temperatures, the grass plant shifts its focus to encouraging green growth, using the nitrogen that was applied. The root system stays undeveloped.

Homeowners have been conditioned to expect a thick, green lush lawn in the spring as soon as temperatures warm. "Part of the problem can be traced back to crabgrass killer combination," states Robson.

Most crabgrass pre-emergence weed killers contain fertilizer to aid in the greening of the lawn. Pre-emergence weed killers must be applied before the weed emerges; since crabgrass germinates by mid-April, most chemical applications are applied by the first of April.

The best bet is to search for a crabgrass or pre-emergence weed killer that does not contain fertilizer. They may be more difficult to find, but they are available. Check with local garden centers, greenhouses or nurseries.

Lawn care services should be contacted to limit early spring nitrogen applications. Lawns can be fertilized in the spring. However, wait until the roots have stopped growing.

Fertilize with a pound of actual nitrogen fertilizer around the middle of May. Check the fertilizer package for proper application information. Remember, though, that spring fertilizing can lead to a higher disease potential.

Many homeowners go to the late fall fertilizer applications, called "winterizers" to stimulate early greening the following spring. Since the nitrogen is absorbed throughout the late fall and early winter, there is no reduction in root growth come spring.

For more information on lawn fertilizer, contact your local Extension office.

Source: David J. Robson, Extension Specialist, Pesticide Safety, drobson@illinois.edu

Pull date: March 15, 2010