Fall fertilization for warm-season turf species 09-24-07

I receive several homeowner calls about this time every year asking if it is too late to fertilize their lawn. My response is usually another question about the health of their lawn and what have been the fertilizer practices so far during the year. A strong healthy lawn probably can do just fine without fall fertilization, but a weak stressed lawn can still benefit from a boost in nutrients.

The first official day of fall just occurred, so we still have several weeks of growing conditions left for most of the state. Late-season or “winterizing fertilizer” applications to 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, nutrients 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 to winterkill, but instead prolongs fall color and earlier recovery in the spring.

Research trials conducted at Mississippi State were designed to simulate worst-case scenario in which Bermudagrass would have an increased likelihood of winterkill by applying highly water soluble nitrogen sources alone or in combination with potassium. Fall and spring color ratings improved with no indication of increasing winterkill potential or affecting total nonstructural carbohydrates. Regardless of time of year, lush turf growth stimulated by excessive nitrogen may be more susceptible to certain diseases and insects, so be prepared to treat accordingly with appropriate fungicides and/or insecticides.

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 24, 2007

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