The most important step of winterizing is spreading a fertilizer...
Winterizing your lawn means preparing your cool season grasses for the harsh winter and the spring ahead. The most important step of winterizing is spreading a fertilizer that will provide the nutrients necessary for your lawn to survive the winter and thrive next spring.
Winterizing should be done in October or November in the northern part of the United States. This gives your grass time to absorb and use the nutrients you have provided to build strong, healthy roots before winter hits. Winterizer fertilizers are high in potassium, helping the grass survive stress and cold. They are also formulated with lower nitrogen than spring fertilizers, which is the ingredient that causes high foliage growth. Late fall foliage growth would take nutrients from the roots and weaken the grass right before winter. Note that these numbers are relative – if you look at the numbers on the bag, nitrogen will probably have a higher number than potassium. However, compared to spring and summer fertilizers, the nitrogen will be lower and the potassium will be higher.
Before you apply a winterizing fertilizer, make sure that your lawn in comprised of only cool-season grasses, such as fescue, Kentucky bluegrass and perennial ryegrass. Cool season grasses experience the most growth in the fall, which is why fall fertilizing is so important. However, warm-season grasses, which are not common in the northern United States, experience the most growth in spring and should never be treated with a winterizing fertilizer as this would weaken the grass plants, possibly beyond repair.
Follow the application instructions found in Fertilizing Basics, as well as the instructions on the bag, to apply winterizing fertilizer. It is important to note that if your region has already experienced a hard frost, it is too late to apply a fertilizer and you should wait until spring to supplement your lawn’s natural nutrients. If your lawn has stopped growing or is starting to turn brown, do not apply fertilizer.
After applying your winterizing fertilizer, raise your mower deck one setting and continue to mow your grass until it stops growing. Make sure you rake falling leaves right away to keep them from smothering your lawn. Then there’s nothing left to do but wait for a healthy, green lawn next spring!