If there are dead spots in your lawn, it is likely that snow mold infections this spring or record-breaking summer heat last year are the cause. Reseeding or “overseeding” bare patches can improve the appearance of a spotty lawn. Now that irrigation water is available and the weather is mild, here is how you can successfully overseed these spots.
1. Grass seed must have direct contact with the soil or young grass plants will not survive after the seed germinates. To improve contact between seed and soil, use a steel garden rake to remove any remaining dead grass or thatch in the dead spots and then use a hand claw or garden trowel to loosen the soil to a depth of one to two inches.
2. Next sprinkle grass seed on the bare spots using the same type of grass that is growing in the rest of the lawn. Most local lawns are predominantly Kentucky bluegrass, so this is the type of grass that most should use for overseeding. However, if the lawn is shaded most of the day, the fine fescue grasses in the original seed or sod mix probably dominate because they are more tolerant of shade. In these areas, fine fescue grass seed should be used. Apply a grass seed “starter” fertilizer at the time of seeding.
Special Note: If crabgrass pre-emergent herbicide has already been applied to your lawn, overseeding this spring will not work because these materials will also prevent the germination of lawn grass seed. You can either overseed in the fall or patch the spots now using sod.
You should be able to find products on the market specifically for seeding bare spots. Some even include fertilizer and mulch along with the seed. However, some of these spot seeding products contain tall fescue grass, a Turfgrass not found in most area lawns.
When this grass grows, its wider blades and clump forming habit will not match well with Kentucky bluegrass or fine fescues, creating a mottled effect. Be sure to check the label of seed products to determine the type of grass seed they contain.
Most products provide a guide on how much seed to apply per square area. You may be tempted to seed more heavily than recommended, but do not. Seed applied too thickly results in crowded young grass plants that will not have space to grow well.
3. After seeding, lightly tamp the seed down using the back of a steel garden rake. Keep the soil slightly moist until the seed germinates and the grass plants become established. It can take two to four weeks for Kentucky bluegrass seed to germinate.
4. The preceding steps are not practical when dealing with very large spots or extensive areas of dead grass. If large areas are in need of repair, slit or vertical seeders are a better option. These are machines that cut down through the existing dead or thin grass into the soil and deposit grass seed into the slits they make in the soil .
If lawn damage (40 percent or more of the square area) is significant, renovation instead of repair may be the best and only sensible option. Renovation involves removing all existing turf and starting over again from seed or sod. For detailed information on renovation consult the Oregon State University Extension publication, Practical Lawn Establishment and Renovation, available online at http://extension.oregonstate.edu/deschutes/sites/default/files/ec1550.pdf. Follow their guidelines for lawns in Central and Eastern Oregon.
Marianne C. Ophardt is a retired horticulturist for Washington State University Benton County Extension.