Most people think about fertilizing the lawn in spring. However, as the weather begins to cool in autumn, applying fertilizer will prepare the grass for winter and the following spring, Known as winterizer fertilizers or winterizes, these fertilizers serve a different purpose from spring fertilizers.
In spring, lawns require a slow-release fertilizer that contains nitrogen that is immediately available to the grass, with some that will release and break-down over an extended period.
For cool-season lawns, winterizers are generally applied in late October or early November after the last mowing of the season. They extend the time that grass will remain green and help sprout green grass earlier in the spring. These slow-release fertilizers contain more potassium and a bit less nitrogen than spring fertilizers. They break down slowly, penetrating the root system throughout the late fall and winter months to optimize shoot development the following spring.
According to David Robson, horticulture educator at the University of Illinois Extension, late fall fertilizers “may be the most important fertilizer you apply to your lawn especially if you’ve never applied one.”
During the winterizing period and as long as the ground isn’t frozen, winterizer fertilizers provide nutrients that the roots will absorb and store. In the spring, typically by mid-March when the air temperature warms up, stored nutrients become immediately available to the lawn to make it lush and green.
Winterizer fertilizing isn’t recommended for mild-winter climates such as in southern California and the deep South where lawns will grow throughout the winter.
Don’t forget though that In spring, it’s important to avoid fertilizing grasses too early as that may limit root growth and stimulate an overly lush top growth.
By: Robin Plaskoff Horton