WE KNOW TURF: Fall Fertilizing

Traditionally, turf grass managers have applied fertilizer during spring and fall using color and the amount of leaf growth as a guide to the rate and frequency of application.

Although promoting good color and stimulating shoot growth are important objectives, frequently overlooked are nutrient influences on carbohydrate reserves, root growth and the plant's ability to tolerate disease and environmental stress. An understanding of the impact of fertilizer applications on these factors can give refinement to a fertilization program.

TIMING APPLICATIONS

An important objective in timing fertilizer applications should be to build carbohydrate reserves and promote root development. The response of warm-season and cool-season turf grasses differ in this respect.

COOL-SEASON GRASSES

The predominant cool-season turf grasses (bluegrass, perennial ryegrass, fescue and bentgrass) initiate and develop their root system in the early spring and fall. For this reason, fall application of nitrogen is paramount to a fertilization program because it will increase carbohydrate reserves and deeper root growth. Fall fertilization will also improve turf density by promoting greater rhizome and tiller growth.

In addition to regular fall fertilization (September - early October), a relatively new concept known as late fall application or late season application has received increasing attention in recent years for inclusion in many maintenance programs. Late fall fertilization is applied when shoot growth slows or approximately at the time of the last regular mowing of the season.

Nitrogen applied at this time greatly enhances the production of carbohydrates. These carbohydrates are stored for use the following growing season, providing early spring green-up and an energy source for turf grasses to recuperate from environmental and mechanical stress.

Another advantage of late fall fertilization is that it reduces the need for high amounts of spring-applied nitrogen. Excessive "spring" fertilization can actually reduce carbohydrate reserves and root development by stimulating rapid shoot growth. This is because growing shoots take priority over roots for carbohydrate utilization.

Both spring and summer fertilization should be used to maintain the color and density produced with fall fertilization the previous year. Fertilization at these times should not produce succulent plant tissue which can increase the severity of turf grass diseases and reduce the plant's ability to withstand heat, drought, mowing or wear stresses.

Application of potassium will greatly contribute to the hardiness of the plant. Potassium increases rooting, promotes wear tolerance, increases drought tolerance and decreases proneness to disease. In addition, potassium will help to "temper" the stimulating effects of nitrogen applications.

WARM-SEASON GRASSES

In contrast, most of the root growth in the warm season grasses, such as bermudagrass, zoysiagrass, centipedegrass, and St. Augustine grass, occurs during the spring and summer. Fertilization during these periods will stimulate root growth. However, only moderate applications of fertilizer should be made in early spring in areas where warm-season grasses experience winter dormancy.

Bermudagrass and St. Augustine grass are subject to spring root dieback following spring green-up. Heavy fertilization during early spring may result in an additional stress during this critical survival period.

Like cool-season turf grasses, warm-season turf grasses accumulate carbohydrate reserves in the fall when shoot growth activity slows. Care must be taken with the timing of fall fertilization since it may decrease low temperature hardiness if applied late. Maintaining adequate potassium levels in fall will increase the tolerance to low temperature.

As with cool-season turf grasses, indiscriminate use of nitrogen fertilization in the summer can increase injury of warmseason grass subjected to disease or environmental stress. As mentioned previously, maintaining adequate soil potassium levels will aid warm-season turf grass in its tolerance of heat, cold, mowing and wear stresses, and reduce its susceptibility to turf grass diseases.