Late season, or winterizing, fertilizer applications for warm-season turfgrasses in Mississippi is a controversial management practice that stems from the concerns for potential winterkill, disease promotion, and the effect on total nonstructural carbohydrates. For high maintenance turfgrasses such as bermudagrass, nitrogen and potassium are nutrients that are required in fairly large amounts during the growing season to provide good growth and quality.
Late fall applications of potassium are a standard recommendation and practice as potassium promotes winter hardiness and disease resistance in turf. Although some research has indicated that late fall nitrogen fertilization increased vulnerability to winterkill and promotion of diseases, other studies have shown no direct correlation. In fact, they show that it prolongs fall color and earlier recovery in the spring.
Research trials were conducted at Mississippi State to simulate the worst case scenario and increase the liklihood of winterkill. Highly water soluble nitrogen sources alone, or in combination with potassium, were applied. The trials found that bermudagrass actually improved in fall and spring color ratings with no indication of increased winterkill potential or total nonstructural carbohydrates . Regardless of time of year, lush turf growth stimulated by excessive nitrogen may be more susceptible to certain diseases.
Considering the poor growing season many lawns have endured this summer, a fall application of a winterizing fertilizer, formulated to contain lower ratios of nitrogen to potassium and particularly with nitrogen sources that are released slowly, may be just what your lawn needs.
Always base your fertilization program on soil test analysis, turf use requirements, and grower expectations. Time the application of winterizing fertilizer in the fall when temperatures begin to moderate and days begin to shorten, but before the turf goes dormant.
Published September 25, 2006
Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu
