Extension Educator, Horticulture
It's time for our yearly discussion about sowing grass seed. For most people the spring surge and urge to work in the lawn has dwindled to a faint spark by the time August rolls around. However, late summer and fall are important times for lawn renovation.
It's not too late to evaluate the lawn. Lawns can decline for a variety of reasons such as improper culture, drought, heat or cold stress, insects or diseases, excessive thatch and unfavorable growing conditions such as shade or poor soil. Combinations of all of the above are also possible. Be sure to consider your expectations of a quality lawn and how realistic they are.
Shade is often a problem. Even shade tolerant grasses need at least two to four hours of sunlight to be successful. In deeply shaded areas consider ground covers or a shade garden. Ground covers such as vinca, English ivy and sweet woodruff interplanted with ferns, hostas and woodland wildflowers make a beautiful and more successful shade garden.
After determining the cause of decline and making necessary improvements, additional grass in bare areas or increasing the density of the lawn may be necessary. In central Illinois the best time to sow grass seed is from August 15 through September. Generally the soil temperature and moisture is high enough for good seed germination. Spring is the second best time to seed grass. Fall seedlings have a chance to develop good root systems before the onset of cold weather and hot dry weather the following summer. Generally there is less competition from annual weed seed germination in a fall seeding than in a spring seeding.
Some lawns may require complete renovations due to poor soil conditions, poor soil drainage, large numbers of weeds and few desirable grasses remaining. However for many lawns, applying seed into the live or dead plants often referred to as "overseeding" may be adequate.
When seeding, be sure to start out with high quality seed at recommended rates. The seed label is an important key when selecting which seed to purchase. For instance, seed purity should be from 90 to 95 percent and seed germination rate should be at least 75 to 80 percent for Kentucky bluegrass. Perennial ryegrass should be higher at 90 to 95 percent. Be sure to read the label for the type of grass included.
Planting different grass species and varieties allows greater resistance to disease and greater adaptability to environmental conditions such as light, soil fertility, moisture and traffic tolerance. A blend is a combination of different varieties of the same species of grass such as Kentucky bluegrass 'Glade' and Kentucky bluegrass 'Eclipse.' A mixture is a combination of different grass species such as Kentucky bluegrass and perennial ryegrass. Many quality mixes contain a mixture of blends.
For successful seeding, the seed must be in good contact with the soil. Seeds just broadcast over the top of live or dead lawns is just an expensive way to feed the birds. Soil in small areas can be roughened with a rake to open the soil. Scatter the seed at recommended rates and use the backside of the rake or a stiff broom to work the seed into the soil. Adequate watering must be available throughout seeding until complete seed germination. The seeds should be continuously watered frequently but lightly. Once the seedlings start to grow, watering should be less frequently, but deeper into the soil.
University of Illinois Fact Sheets available through the University of Illinois Extension: