Turfgrass establishment following a hot, dry summer
Following the summer of 2012, many turfgrass areas and lawns may need to be over-seeded to fill in damaged or dead areas.
The summer of 2012 will forever be burned in the weather record books and the minds of turf managers across Michigan. The combination of drought and high temperatures stressed cool-season turfgrasses and in some areas the verdict has yet to be delivered on whether it was life or death.
The rainfall that most areas of the state received between August 9-12 (East Lansing, Mich., area approximately 1.5 inches) and the cooler temperatures, especially night temperatures, has resulted in many unirrigated turf areas jumping back to life. In some cases, I’ve already heard people complaining about the aggressive top-growth and need for frequent mowing. However, I can still find turf areas that were stressed that are slow to revive, i.e., maybe dead, and the forecast of warmer and potentially dry weather in the future isn’t going to favor these already stressed patches of turf.
Although the forecast may not be ideal for reestablishment if you don’t have access to irrigation, this is still the best time of year to try and establish turfgrass. In addition to reduced competition from annual weeds such as crabgrass, shorter day length means less time for daytime drying of the soil. The following establishment primer will help ensure any attempts to grow new turf this fall are successful.
Reseeding damaged areas
The first decision that needs to be made is whether to spot-seed the bare areas or if the whole area needs to be reseeded. This decision is basically one of practicality. If the turf was simply thinned or there are small patches of dead grass about the size of baseballs, a fall fertilizer application and favorable weather conditions should help the existing turfgrass to recover and fill in those bare spots. If the damaged areas are the size of soccer balls or larger, or if the area only has sporadic green turf plants, then over-seeding is going to be necessary to restore the area to turf. In some cases, if the complete lawn was lost, sodding is certainly an option to consider.
Another consideration on the site is to assess weed pressure. Following the recent rains, many weeds have surged in taking over previously dormant turf areas. If the turf is covered in crabgrass, it’s going to be difficult to have new seedlings compete with crabgrass. If weed competition is severe, make sure to kill the weeds before attempting reestablishment.
Tools to renovate
There are a number of different methods to ensure that reseeding efforts are successful. First and foremost, you must ensure that you get good seed-to-soil contact, i.e., seed sitting on top of the soil or simply broadcast spread onto the turf without creating any holes or slits will feed the birds, but not be much use for growing new turfgrass. There are several options for creating the holes or slits to ensure seed-to soil contact. Machines such as core aerifiers, power rakes, slit seeders or even hand raking small areas will get the job done.
For established areas that may just need a light over-seeding to improve density, core aerification is a viable option. It’ll also give you the benefit of improving soil aeration that is critical for many sites that have compacted soils or high clay content soils. For areas that suffered extensive turf loss, slit seeders are the best option. Slit seeders create a slice in the soil that the seed falls directly into and ensures good seed-to-soil contact. To improve establishment, slit seed in at least two directions. Many lawn care companies offer this service or if you’re a do-it-yourselfer, these devices might be available at a local rental store.
Species, seeding depth and rates
Making sure you have the correct species and cultivar, especially if you are over-seeding an existing lawn, is a critical step to ensure satisfaction. One common frustration many homeowners have after over-seeding is that the newly seeded turf has a drastically different color and appearance than the existing turf stand. To avoid this problem, I would suggest you do your homework to try and find out if you know the specific species and cultivar that was originally established. In most areas if you’re not sure of the turfgrass species on the lawn, odds are it’s Kentucky bluegrass, so select Kentucky bluegrass cultivars to reseed the turf.
If, however, you are completely renovating an area and are looking for something a little different that might be able to withstand drought conditions better, consider tall fescue. Look for key words on the seed bag such as Turf type, Improved or Dwarf when selecting tall fescue cultivars. I would avoid the standard Kentucky 31 (K-31) tall fescue for use in home lawns due to its wide leaf blade. Turf type tall fescue is now being mixed with Kentucky bluegrass and is more widely available to consumers than it was just a few years ago. Please see our factsheet, Purchasing Quality Turfgrass Seed: Read the Label, at www.turf.msu.edu under the Home Lawns section for more tips on purchasing seed.
Over-seeding rates for Kentucky bluegrass are 1.5 to 2 lbs./1,000 sq. ft. For mixtures containing perennial ryegrass or fine fescues, rates should be increased to 3 to 5 lbs./1,000 sq. ft. For tall fescue the seeding, not over seeding, rate is 6 to 8 lbs./1,000 sq. ft. Strive to incorporate the seed to a depth of about 0.25 inches. Deeper planting depths may result in some of the germinating plants not making it to the surface.
Consider mulch for moisture retention
Spreading a light mulch cover on top of the newly seeded area will help the soil retain moisture and keep the seedlings from drying out. However, if you are seeding into an existing turf stand and did not remove all of the dead turfgrass, the existing turf will essentially serve as a mulch cover. The recommended rate for using straw mulch is one bale of straw/1,000 sq. ft.
Be careful with the amount of mulch you apply – you don’t want to smother those young seedlings. Apply enough so you can still see about one-third to one-half of the soil underneath.
There are also numerous, more sophisticated mulch products that are easier to spread than straw and expand with moisture to cover the soil. Even something as simple as turf clippings can be used as mulch – just don’t spread them too thick over the area.
Fertilizer, irrigation and herbicides
At the time of seeding, apply a starter fertilizer at a rate of 1 lb. N/1,000 sq. ft. to help those young seedlings get established. A starter fertilizer is a fertilizer with a N:P2O5 ratio similar to 1:1 or 1:1.5. Under the phosphorus restriction legislation that is in place, starter fertilizer is still allowed for turfgrass establishment. The maximum amount of phosphorus that can be applied in a single application is 1.5 lbs. P2O5/1,000 ft.2 with a yearly maximum of 2.5 lbs. P2O5/1,000 ft.2.
If you have the time to take a soil test, follow the soil test recommendations for establishment. Homeowners can purchase a soil testing kit from the MSU Extension bookstore. More information on soil testing can be found at www.msusoiltest.com.
Make sure to keep the seeded area moist throughout establishment. In many cases, this may require watering several times a day. A good mulch cover will help the area stay moist, so the site may be watered less frequently. Water lightly when irrigating; there is no need to see water puddling or running off the site.
To be safe, avoid applying all herbicides this fall, i.e., no weed-and-feed products. Young seedlings don’t tolerate herbicides very well and the guideline is usually to wait three "real" mowings before applying any herbicides or, in some cases, at least 60 days. By real mowings, I mean you’re actually cutting significant grass, not just running over the area to trim down any weeds.
Some herbicides can be safely applied at seeding, but remember that one of the reasons fall establishment is favored is the general lack of weed competition. So although some herbicides are safe at establishment, they are generally not necessary this time of year. Always make sure to read and follow the label directions before applying any herbicide.
Finally, don’t be afraid to get out there and mow the new turf. It’s always challenging to set absolute guidelines when talking about when you should start mowing new seedings. My recommendation: don’t wait until the seedlings are so tall they’re starting to fall over. If you typically mow your lawn at 3 inches, start mowing the newly established areas when the seedlings get to or slightly exceed the 3-inch height. Mowing turf helps it spread laterally and fill the area, so start those engines as soon as you start to see the grass creep up to your established cutting height.
Hopefully, these tips will help you reclaim those bare areas and get the turf off the blocks quickly next spring.
- MSU Extension’s Drought Resources
- Fall lawn care tips from MSU turfgrass expert Kevin Frank, interview with Greening of the Great Lakes
Dr. Frank's work is funded in part by MSU's AgBioResearch.