Winter Overseeding

Warm-season turfgrasses go dormant with sustained cooler temperatures from late fall to early spring. Dormancy is marked by a period where turfgrasses cease growth because of unfavorable environmental conditions but can resume growth once suitable environmental conditions exist. During winter dormancy, shoots of warm-season turfgrass species turn brown or off-colored. To some homeowners this change in leaf color is unsightly, so they choose to seed a cool-season turgrass within the warm-season turfgrass canopy. It is important to note that the decision to overseed a warm-season turfgrass is typically done for aesthetics and not for agronomic reasons. Over time the continued practice of winter overseeding can lead to less dense warm-season turgrasses, especially if the cool-season turfgrass is not transitioned out early in the growing season.

When to seed

Winter overseeding should take place beginning in October as warm-season grass growth slows. Seeding can be done throughout late fall and winter, but extremely cool weather may negatively affect germination and plant growth.

Seed application

Step 1: Determine which turfgrass species, annual ryegrass or perennial ryegrass, will be used to overseed the lawn. Calculate the amount of pure live seed (PLS) you will need. The recommended seeding rate for both annual and perennial ryegrass is 5 to 10 pounds PLS per 1,000 square feet.

Step 2: Calibrate the drop spreader or rotary spreader before applying seed to the lawn.

Step 3: Prior to seeding, the turfgrass needs to be mowed. This will allow seed to move into the turfgrass canopy for better seed-to-soil contact and better germination. To increase seed-to-soil contact after seeding, irrigate after seed application, add a light topdressing of sand, use a slit seeder or lightly rake the area to work seed into the canopy.

Step 4: Evenly distribute the seed across the lawn. Applying in two directions, as illustrated on the next page, is recommended. Over-application in areas can lead to thicker stands and an uneven appearance. Improper application can also lead to some areas not receiving seed, which will become evident as the seed germinates.

Post-seed application maintenance

Irrigation: Irrigation frequency will depend on environmental conditions. Once the lawn has been overseeded, the soil should be kept moist until seedlings emerge. Once seedlings emerge and begin to grow, irrigation should be applied less frequently over time. This will encourage deeper rooting by the turfgrass. Be sure not to irrigate to a point of surface runoff and take rainfall into account when scheduling irrigation.

Nitrogen Fertilization: Fertilize 10 to 14 days after turfgrass plants emerge from the soil. Fertilizer with up to 0.5 pounds of nitrogen per 1,000 square feet. Subsequent nitrogen fertilization may be necessary as the turfgrass establishes. Be careful not to overfertilize the turfgrass with nitrogen. Never apply above 1 pound of nitrogen per 1,000 square feet per application. Fertilize only when the turfgrass is actively growing. Follow soil test recommendations for proper fertility.

Mowing and Traffic: Mow both annual and perennial ryegrass at 1 to 2.5 inches routinely during the growing season. During the establishment period it is best to limit traffic across the area to prevent turfgrass stress and surface disruption. Mowing should be initiated once the turfgrass reaches a point of sufficient growth that mowing will not damage the turf. Make sure the soil is not saturated so that a mower does not rut or compact the soil. Never remove more than one-third of the leaf blade at one mowing. Mowing at the appropriate height and frequency iskey to having a healthy turfgrass by preventing scalping and reducing weed encroachment.

Annual ryegrass overseeding

Spring transition

Warm-season turfgrasses will break dormancy as soil and air temperature increase in spring. This marks a period known as spring transition in which the warm-season turfgrass and cool-season turfgrass are competing for water, nutrients and sunlight. Cultural and chemical means can be implemented to encourage warm-season turfgrass growth while hindering cool-season turfgrass growth.

Cultural: The key to cultural practices successfully aiding spring transition is to implement these practices to stress the cool-season turfgrass but not overstress the warm-season turfgrass. Lowering the mowing height and limiting irrigation can put the cool-season turfgrass under stress while allowing the warm-season turfgrass to be more competitive. However, be careful that these cultural practices are implemented during warmer weather — once temperatures are consistently between 65 to 87 degrees Fahrenheit. Other cultural practices, such as vertical mowing and aerification, can disrupt the cool-season turfgrass and place the cool-season turfgrass under stress if implemented under warmer temperatures.

Chemical: In addition to cultural practices, herbicide applications may be required to achieve removal of cool-season species during spring transition. The herbicides listed in the table below are labeled for cool-season turfgrass control in warm-season turfgrass species that are commonly grown in Louisiana.

When applying any type of herbicide, you must follow the manufacturer's labeled directions. For more information regarding pesticides for turfgrass species please reference the Louisiana Suggested Chemical Weed Control Guide.

Download here: Louisiana Home Lawn Series: Winter Overseeding 3624-KKK