Garfield County Cooperative Extension

Perfect time to overseed cool season shady lawn areas

Rick Nelson Extension Educator, Ag/4-H

Caring for the lawn during 2016 has been like riding a roller coaster. It has been a year in which the pendulum has swung widely from cool to warm and wet to dry.

These ever-changing conditions are not only hard on us but also our lawns. Many of us have dead spots in our bluegrass and tall fescue shady areas. Early to mid-September is the ideal time to overseed and thicken up that thinner stand with almost guaranteed success.

High soil temperatures, cooler nighttime temperatures and hopefully more rain make perfect conditions for quick germination and the establishment of turf from seed.

Soil preparation, seed selection, fertilization and irrigation are important keys to overseeding.

Prepare the area by core aerating and/or verticutting to break up soil compaction and loosen the crust. Verticutting slices grooves in the soil, creating an area for grass seed to fall. This method is preferred as it provides for the most even seed bed. Start by mowing the grass short (1 to 1.5 inches) and then verticut in one or two directions. Rake and remove any debris from the lawn for good seed-to-soil contact.

High quality seed is a must. Avoid inexpensive seed blends that contains species such as creeping red fescue, fine leaf fescue, perennial, annual rye and annual bluegrass. These species may look good quickly after seeding, but they are sure to fail under next year’s stressful summer conditions. Check the seed label to ensure you are getting good varieties of bluegrass or tall fescue. No other grass species will tolerate local conditions.

New seedlings need fertilizer to help them establish and quickly develop. Unlike the standard grass fertilizer that is high in nitrogen, new seed should be fertilized with a balanced fertilizer such as 13-13-13 or a high-phosphorus product such as 10-20-10.


Phosphorus is a macronutrient that aids in the root development of young seedlings. Fertilizer should be applied at the rate suggested by a soil test (available through your local extension office), or a starter fertilizer should be used at the rate suggested on the bag. The existing grass will benefit from a September fertilizer application.

Most homeowners do not apply enough fertilizer when seeding. They are afraid of burning the new grass. In fact, the opposite happens. If there is a lack of nutrition, the seedlings fail to grow. About four weeks after germination, apply a high-nitrogen fertilizer such as 27-3-3 or 30-0-0 at labeled rates. This application should be repeated in mid-November to send the grass into winter strong.

Determining the correct seeding rate is important. Seed is usually applied at about half the seeding rate that is used for new lawns on bare soil.

For tall fescue, the normal rate is 6 to 8 pounds per 1,000 square feet, so the overseeding rate is 3 to 4 pounds per 1,000 square feet. This should be broadcast over the prepared area. The new-lawn rate for bluegrass is 3 to 4 pounds per 1,000 square feet, which makes the overseeding rate around 2 pounds. Adjust the seeding rates up or down based on the current stand of grass in your lawn. Fescue should germinate in about 10 days, while bluegrass may take up to two weeks.

Once the seed is sown, the seedbed must be constantly moist to ensure rapid germination. At seeding this will require frequent, light irrigation to keep the upper surface moist at all times. As the seed starts to germinate and establish, the watering schedule can become progressively deeper and more infrequent.

Remember, the ideal window to overseed is very short. The greatest success is achieved by having the seed planted by end of September.

Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Oklahoma Cooperative Extension Service is implied.

 

Oklahoma State University, U. S. Department of Agriculture, State and Local governments cooperating.  Oklahoma State University in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal and state laws and regulations, does not discriminate on the basis of race, color, national origin, gender, age, religion, disability, or status as a veteran in any of its policies, practices, or procedures."

 

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