Almost all lawns, both in the North and in the South, will react to the cooler weather in the fall by entering a period of dormancy or extremely slow growth. Just prior to this period of dormancy is the time you should apply your last fertilization application. This is probably the best time to fertilize your lawn for the maximum results. While it's not important to maintain a green lawn long into the cold months of winter, it is important for your lawn's roots to continue growing as long as possible. This underground growth results in healthier grass plants for the following year. This last treatment is often called a Winterization Feeding.
Because the ideal Winterization Feeding is primarily for the root system, the components of this final fertilization may be a little different than a normal fertilizer application.
But what exactly is winterizer, and why is it important to the lawn? Well, winterizing has several benefits.
In the fall, grass is actually storing nutrients for the approaching cold weather. This is typical of most perennials which most turfgrasses are, with the exception of a few, like annual ryegrass.
When the turfgrass is storing energy, the single most important nutrient at that time is phosphorus. Its key role is in the storage and transfer of energy within the plant and root system-- and that is what grass is doing in the late fall. Phosphorus also promotes stronger roots and it helps grass become more tolerant of diseases, heat, cold and drought.
Finally, a Winterization Feeding gives a healthy dose of potassium to your lawn which helps protect the lawn during the winter as it promotes a tolerance to the cold weather and foot traffic, which can severely damage a lawn during extremely cold weather.
The question is: should you buy a product that specifically specifies it to be a "Winterizer Fertilizer?" Actually, if you have leftover fertilizer from earlier in the year, go ahead and use that. The difference between the two types is minute. If you have to buy fertilizer for that final feeding, go with the product that is labeled Winterizer just for that little additional phosphorus it contains. The important thing is to put some type of fertilizer down in late fall. Whether your bag of fertilizer is labeled Winter or not, your grass won't be able to tell the difference.
There are also Winterizer products available that control weeds. Just make sure you apply while the weeds are still actively growing. In the north, that means no later than mid October.