Frosty nights when temperatures fall into the low 30s but stay above 32 degrees Fahrenheit can mark the end of the growing season for many perennial turf grasses and damage or kill annual grasses. Fortunately, permanent lawns typically contain perennial grasses. The effects of frost on perennial grasses varies with their variety, but your response should not change.
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Frost harms grass plant tissues by triggering increased transpiration -- sending moisture through plant pores, or stoma. That moisture and airborne moisture coat and protect plant tissues. During periods of calm wind on a clear night, moisture can freeze on the surface of grass, forming frost, dehydrating the blades, or leaves, and making them brittle.
The first rule after a frosty night is to stay off the grass until the air warms. Keeping weight off grass avoids leaf breakage. The thawing frost can rehydrate the leaves.
Annual, Biennial and Perennial Grasses
A lawn containing an annual grass must be reseeded after a frost in order for the lawn to remain. Typically, annual grass is used to fill a lawn until a slower-germinating perennial grass becomes established. Some biennial grasses survive frosts. They include Italian ryegrass (Lolium italicum), also called annual ryegrass despite being biennial in U.S. Department of Agriculture plant hardiness zones 4 through 8.
After a frost, keep perennial turfgrass hydrated. Most grass needs 1 inch of water weekly, including rainfall. Continue watering the grass as it enters dormancy when temperatures cool, but never allow water to puddle, which cuts off the roots' access to air and light.
Perennial warm-season grasses, which live several years and include St. Augustinegrass (Stenotaphrum secundatum, USDA zones 8 through 10), may enter dormancy when the temperature dips into the 40s Fahrenheit. Cool-season perennial grasses such as Kentucky bluegrass (Poa pratensis, USDA zones 2 through 6) need temperatures below freezing to enter dormancy.
Perennial grasses turn brown and become dormant after a freeze, but their roots and crowns keep growing. The crown is where roots and leaves or stems meet.
Minimize damage caused by frost by choosing grass best adapted to grow in your area. Cool-season grasses grow in spring and fall spurts. They are typically planted in mixtures -- Kentucky bluegrass for full sun, perennial ryegrass (Lolium perenne, USDA zones 3 through 6) for early growth, fescue (Festuca spp., USDA zones 3 or 4 through 7, depending on the variety) for shade.
Warm-season grasses grow throughout mild winters and into early summers. A warm-season lawn typically has only one kind of grass, such as zoysiagrass (Zoysia japonica, USDA zones 5 through 10) or St. Augustinegrass.
- Keep grass hydrated. With rain and/or irrigation, grass should receive 1 inch of water per week until the first hard freeze, when temperatures fall below 32 degrees Fahrenheit.
- Mow grass to make it 2 to 3 inches tall when cold weather threatens. That height gives it extra tissue to lose to frost and provides insulation for its crowns.
- Wait for temperatures to warm into the 40s Fahrenheit and grass blades to thaw before mowing warm-season grasses after a frost.
- Mow cool-season grasses after frosty nights only if they are still growing. Don't mow dormant grass; wait until it greens up in spring.
- Sharpen lawn mower blades for late-fall cuttings. Dull mower blades chew up recently thawed grass blades.
Do not rake or fertilize a lawn after a freeze. Raking may damage crowns, and fertilizer produces tender plant growth that might be damaged in subsequent cold weather.
Cold-weather lawn work can be rough on your hands. Wear garden gloves when mowing grass and handling tools.