Lawn grasses are commonly organized into two major groups: cool-season and warm-season. Before fertilizing, you need to determine the type of grass you have and the typical growth cycles for your area. Different types of grasses call for different types of fertilizers. Choosing incorrectly can be devastating for your lawn, weakening its hardiness, putting it at risk of injury, pests or diseases, even "burning" it. Fertilizing too early or too late can also put your lawn at risk.
The information below can help you determine the type of grass in your lawn and when you should fertilize. Still unsure? Contact your local Cooperative Extension System office, consult your local nursery or check online resources such as BioAdvanced.com.
Cool-season grasses include Kentucky Bluegrass, Fescues, Bentgrass and Ryegrasses. They are often referred to as "northern grasses" because they are hardy and well adapted to cold winter climates. Cool-season grasses grow vigorously in the cool months of fall and spring. Growth slows in the heat of the summer. These grasses go dormant and turn brown in cold winter areas where the soil freezes. Where winters are not quite as cold and the ground doesn't usually freeze, such as in the West and the transition zones of the Midwest, cool-season lawns stay green all winter. With proper water, they also stay green all summer.
The most important time to fertilize cool-season lawns is in fall and spring, prior to periods of vigorous growth. In cold winter areas, you should not fertilize in spring until the grass is "greening-up" and has started to grow. In most areas, cool-season grasses are not fertilized in the heat of summer. Summer feeding can weaken the turf and promote disease.
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Warm-season grasses include Bermudagrass, St. Augustinegrass, Centipedegrass, Zoysiagrass, Bahiagrass and Carpetgrass. They are often called southern grasses because they grow best in hot summer areas and lack the winter hardiness of the cool-season grasses. Depending on location, warm-season grasses grow vigorously from mid- to late spring through summer and into early fall. They usually turn brown and go dormant in winter.
The most important time to feed warm-season lawns is from spring through summer and, in some southernmost areas, into fall. Warm-season lawns should not be fertilized prior to active growth in spring (wait until you have mowed the lawn twice) or late into the fall (six weeks prior to the average date of the first frost). Either practice can weaken the turf and lessen hardiness.
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Remember: Your local Cooperative Extension System office can give you exact fertilizer timing for your area and grass type.