If you’ve been to a local garden center lately, there’s a good chance you’ve seen some displays marketing winterizer fertilizer for your lawn. Many of these displays are quite shiny and state all sorts of reasons why you should apply fertilizer to prepare your lawn for winter.
However, as with most purchases, a little consumer research is a good idea before being persuaded by those glossy ads. Where do you find such non-biased, evidence-based information on lawn and garden topics in Florida? UF/IFAS Extension, of course!
UF/IFAS research has found that for warm-season grass species used for North Florida lawns, the last application of fertilizer should occur no later than September. Why so? Well, similar to deciduous tree species, our warm-season grasses, including centipede, St. Augustine, bahia, and zoysia, are adapted to go dormant at the onset of cooler weather.
Once the transition into dormancy begins, the turf is not actively growing, therefore nutrient uptake slows down. Eventually, the turf becomes brown and will remain that way until warmer spring temperatures initiate active growth again.
What about all the glossy ad’s claims regarding improved root growth? When looking over the N-P-K values of winterizer fertilizers, you will notice that most have a high third number, indicating a greater proportion of potassium. Research does show that adequate potassium levels do make turf more resilient to stress. However, if the turf has been maintained properly throughout the year – proper mowing height, irrigation, and fertilization – then the lawn’s root systems are likely strong enough to get it through winter.
Winterizer fertilizers that contain a high proportion of nitrogen, say over a 5 on the N-P-K analysis, can actually cause your lawn harm. Nitrogen promotes leaf and shoot growth, which is tender to damage from cold weather. If these type products are applied late in the year, new growth is likely to be nipped by a cold snap, causing stress to the lawn, which can lead to greater pest pressure and poor growth the following spring.
For a healthy lawn, there’s no substitute for year-long good care. If you are having a lawn issue or would like more information on fertilizing lawns, please call your local Extension Office or check out some of UF/IFAS’s online resources!