Winter is mainly a time to stop fertilizing a lawn. Because a lawn is not growing and using nutrients in the soil, fertilizing too late into the winter can harm a lawn. Grass can benefit from a lawn treatment in preparation for the winter, but it cannot be done too late into the cold season. Fertilizing at the right time can help protect grass during the winter months and nourish it into early spring.
A gardener must be careful to choose the right time to fertilize in preparation for winter. Because the right time can differ by climate, a lawn gardener can use grass growth to gauge the right time for a cool-weather fertilizer application. According to Berks County Cooperative Extension of Penn State College of Agricultural Sciences, grass should receive its late fall fertilization when it begins growing too slowly to require mowing. In warm climates with an early thaw, a late-winter application of fertilizer toward the end of February can be beneficial.
The time frame for winter fertilization depends heavily on the type of grass and the climate. Cool-season grasses take fertilizer later into the fall than warm-season grasses. Lawn gardeners should usually avoid fertilizing a lawn in December and January. In most areas, plants can benefit from fertilizer again in late February to early March. In most areas of the United States, this happens around Thanksgiving. One exception is in warm climates located close to the equator, like conditions found in Hawai'i, where fertilization in the warmer winter is reduced but not stopped completely.
Fertilizing in the late fall to prepare for the winter helps bulk up plant roots, providing them with extra resources to carry them through their dormant period in the cold months. This can be compared to a hibernating bear gathering a layer of fat to keep him warm and fed through the winter.
For a winter preparation fertilizer application, the most common type of fertilizer is slow-release nitrogen. Slow-release nitrogen often comes in granules, which can be like grains of sand or little ball bearings. Over time, the granules release a measured amount of nitrogen, which feeds the lawn for several months at a time. Slow-release fertilizer is preferable to fast-absorbing granulated fertilizer for winter applications because the late cool-weather fertilizer application needs to last several months through the winter to maintain the health of the grass.
Fertilizing too late can damage a lawn rather than help it. Adding fertilizer too early in the fall can increase the chance of insect infestations in a lawn, including root-sucking chinch bugs. How much fertilizer is necessary depends on the type of grass, and should be calculated carefully to avoid causing fertilizer chemical burns on the lawn.