On your turf, it's best to return to roots

Fertilizing lawns in the early spring may not be the best for the grass in the long run.

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

That's because most Illinois lawns are composed of cool season grasses such as Kentucky bluegrass, turf-type tall fescue and perennial rye grass. Shady areas may contain creeping, red or chewings fescue. These grasses remain actively growing as long as temperatures are lower than 85 degrees F.

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

So, 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".

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 is penalized. Turf may be stressed when summer arrives and temperatures climb and rainfall is less.

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 the crabgrass-killer combination.

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 in central Illinois, most chemical applications are applied by the first of April. Products are applied a couple weeks earlier in southern Illinois.

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

Another recommendation is to contact lawn care services 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 potential for disease.

Many homeowners use 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 when spring arrives.

This column was written by David J. Robson, University of Illinois Extension Educator, Horticulture.