According to our garden calendars, it’s time to overseed our cool-season lawns. Homeowners have been asking a lot of good questions:
- Why overseed and how to do it?
- What about the heat, drought, and water restrictions?
Let’s dig in to overseeding—no shovels required.
Overseeding Basics
Overseeding is the process of incorporating new seed into an existing lawn to maintain its health by thickening the turf canopy and repairing bare areas. It is recommended if lawns are in a less-than-desirable condition due to mismanagement or stress from heat, drought, weed, disease, and insect pressure. The best time to overseed cool-season turf like Kentucky bluegrass and tall fescue in eastern Nebraska is between August 15 and September 15. This is because of favorable environmental conditions for growth (i.e., warm days and cooler nights) and less weed competition.
Selecting Grass Seed
Choosing the right grass and purchasing quality seed are an important first step in the process. Consider growing requirements, maintenance needs, pest problems, durability to foot traffic, and aesthetics when choosing turf species. Visit a local, reputable retailer to purchase blue or gold tag certified seed. These tested bags of quality seed will contain 2-4 dependably recommended cultivars. This may cost more, but you truly get what you pay for.
How to Overseed
Good seed-soil contact is a critical factor in overseeding success. For small areas, this can be accomplished by raking with either a stiff-tined or a poly leaf rake to break the soil surface, seeding by hand, and raking again to work the seed into the soil. For larger areas, core aeration removes plugs of soil to reduce compaction. Mow over the cores after they’ve dried to distribute the soil and make a nice seedbed. Power rake when thatch is greater than ½ inch in more extensive renovation situations. Apply seed in different directions using a drop spreader to ensure good coverage.
Care After Overseeding
- Irrigation in the first week after overseeding is critical. The seed requires adequate moisture to germinate, and the plant is vulnerable to drying out because the root system is small. Water daily (and up to 3 times a day) to a ½ to 1 inch depth during the first week to keep the seedbed moist, and gradually lessen over time.
- Begin mowing at the highest setting when new grass reaches approaches height of existing grass, in about 3-6 weeks. Do not remove more than 1/3 of the blade at any time, and consecutive mowings may be required to get turf to the desired height.
- New grass seedlings require additional fall fertilization. Apply a starter fertilizer 4 weeks after germination or a more common high nitrogen fertilizer at 10 weeks after germination. If weed pressure has been high in the past, consider a starter fertilizer product containing the active ingredient mesotrione.
Other Factors to Consider
The Omaha metro’s public water utility, MUD, has recommended voluntary outdoor watering restrictions until further notice. They ask that customers limit their use to 2 of the 3 possible days per week based on home address: even house numbers (i.e., Tuesday, Thursday, Saturday) and odd house numbers (i.e., Wednesday, Friday, Sunday). According to MUD, watering “new sod” is permitted, but they do not mention specifically new seedings and renovations.
Air temperatures above 80°F can impact seed growth. Given high temperatures and water restrictions, delaying overseeding until more favorable growing conditions may be an option. Tall fescue can be seeded until August 31st to give it time to establish before the average first frost, while Kentucky bluegrass can be seeded until September 15th.
If conditions or restrictions do not ease, dormant seeding is another option. This practice is when seed is put down after the ground is frozen, usually between December and March. The seed will germinate while temperatures are cool and rains are (hopefully!) abundant. Soil surface should be loosened beforehand similarly to traditional overseeding.
Once watering of new seeds has begun, homeowners will want to continue watering. The newly germinated seedling is most vulnerable to drying out since the root system is so small. Because of the tough growing conditions, homeowners should evaluate the seed germination rate in early September and apply additional seeds if the rate is less than 50%.
Further Reading
More info about watering restrictions in Omaha in August 2023 here, fall overseeding here, dormant seeding here, and Nebraska Extension’s general cool-season lawn calendar here.
Reviewed by John Fech
