Late season lawn fertilization 09-29-08

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.

Although some research has indicated that late fall nitrogen fertilization increased vulnerability to winterkill and promotion of diseases, other studies, including those conducted by Mississippi State University, have shown no direct correlation to winterkill. Instead, research found that it prolongs fall color and promotes earlier recovery in the spring.

Late fall applications of potassium are a standard recommendation and practice as potassium promotes winter hardiness and disease resistance in turf. 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 has just recently occurred, so we still have several weeks of growing conditions left for most of the state.

Therefore, 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. Time the winterizing fertilizer application when temperatures begin to moderate and days begin to shorten, but before the turf goes dormant.

Regardless of time of year, lush turf growth stimulated by excessive nitrogen may be more susceptible to certain diseases and insects. Be prepared to treat accordingly with appropriate fungicides and/or insecticides. Always base your lawn fertilization program on soil test analysis, turf use requirements, and grower expectations.

Published September 29, 2008

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