Correct fertilizer key to Fall lawn preparation

Correct fertilizer key to Fall lawn preparation

By Theresa Friday

September marks the beginning of the fall gardening season. Now is the time to start preparing your lawn for the winter.

One area of confusion for many gardeners is fall fertilization. Applying the proper amount of fertilizer for your grass will help to promote a vigorous, healthy lawn that can out-compete weeds and serve as a filter to protect Florida's ground and surface waters.

However, applying the wrong fertilizer at the wrong time can be devastating to a lawn.

In Northwest Florida, it is generally recommended that the last fertilization of the year be applied in early to mid September.

But what type of fertilizer is the best? It’s important to be very selective in your choice of fertilizer.

For your lawn’s September application, consider a low nitrogen, high potassium fertilizer such as a 5-0-15, 5-0-20 or a 5-5-30. These may be referred to as “winterizers” because they prepare your lawn for winter.

However, do not be misled by the term “winterizer” fertilizer. Many fertilizers advertised as winterizers are very high in nitrogen and are NOT good choices for a late season application. A good winterizing type fertilizer should contain two to three times more potassium than nitrogen.

Just as a refresher, nitrogen is always the first number in the fertilizer analysis.

Phosphorus is the second number and potassium is the third. Unless a soil test indicates a need for phosphorus, we generally recommend no or low-phosphorus fertilizers because phosphorus can be a major pollutant of our surface water.

Turfgrass researchers at the University of Florida have seen that an increase in the potassium to nitrogen ratio in grass tissue will increase the winter hardiness of a grass.

Applying a fertilizer with a high nitrogen content can cause a flush of new growth too late in the year. It’s equivalent to drinking a lot of regular coffee before going to bed. The nitrogen “wakes” the grass up, forcing the lawn to produce new tender growth at the wrong time of year.

Young tender growth is very susceptible to cold injury and is likely to be damaged by the first frost. This weakens the lawn and many times the damage goes unnoticed until the following spring when sections of the lawn do not green up.

Avoid winterizers such as 22-3-14, a common analysis marketed by some major companies, but more appropriate for northern grasses than for southern grasses at this time of year.

And don’t forget your lawn during dry weather in the fall. Whenever the grass wilts and the lawn turns grayish, water it. Apply one-half inch of water at each application. If you do this, you won’t have to water often, but your lawn should green up much better next spring.

What if you have weeds in your lawn now? Forget them unless you can hand pull. If you try putting on a herbicide in hot weather, you will likely do as much damage to your lawn as to the weeds. Most of the weeds there now will die during the winter.

The primary secret to weed control is focusing on keeping your lawn healthy, not killing the weeds. A healthy lawn gives little space for weeds to grow.

If you want to use herbicides, rely primarily on pre-emergent herbicides to prevent the weeds from emerging. The timing for a pre-emergent herbicide to prevent cool-season weeds is in October. The timing for preventing most warm-season weeds is early March. Unfortunately, neither one of these times is good for applying fertilizer, so avoid weed-and-feed fertilizers.

Theresa Friday is the Residential Horticulture Extension Agent for Santa Rosa County. The use of trade names, if used in this article, is solely for the purpose of providing specific information. It is not a guarantee, warranty, or endorsement of the product name(s) and does not signify that they are approved to the exclusion of others.

For additional information about all of the county extension services and other articles of interest go to: University of Florida