How late can you seed?

We are out of the optimum window for seeding turfgrasses in Indiana. However, many are still hoping to seed. Following is a summary of our studies in the early 90’s on seeding at less than optimum times of the year.

1.  For optimum establishment, seeding should be done in late August or early September. Waiting as long as until Oct. can severely reduce establishment before winter, especially with the slower establishing Kentucky bluegrass (Fig. 1). 
    It is also important to seed early enough in fall to allow seedlings to mature to the point where they can withstand the stresses of winter. This was evident with perennial ryegrass seeded in Nov. 1990 which did not survive the winter (Fig. 2). The soil temperatures were warm enough to allow germination in Nov., but the temperatures cooled too quickly to allow maturation of the ryegrass before winter. 
    Do not seed when soil temperatures are warm enough for germination, but when there is not enough time left before winter for good establishment. It is be better to seed after soil temperatures cool so germination will not occur until the following spring. This is defined as dormant seeding and it is usually more effective than spring seeding and only slightly less effective than Sep. seeding (Fig. 3) A possible problem with dormant seeding of quick-germinating species like perennial ryegrass is with unusually early spring warm spells, the seeds may germinate, only to die with ensuing cold temperatures. Therefore dormant seeding works much better from Bloomington and north because of colder winters.
    Turfgrass seeded at less than optimum times is often slow to fill in which allows many weeds to germinate and establish. This is especially problematic with Kentucky bluegrass. In our studies, Kentucky bluegrass seeded in May had over 3 times more weed infestation than Kentucky bluegrass seeded in Sep. (Fig. 4). Weed control in newly established turf is difficult because most herbicides are not labeled for use on turfgrass seedlings.
    An important consideration when seeding turf at non-optimum times and even optimum times of the year is that even though establishment is slow, the turf will eventually fill in. As long as the seeds or seedlings are not damaged, the grass plants will mature and gradually fill in. Even though Oct. 1 is one of the poorest times for seeding Kentucky bluegrass, plots of bluegrass seeded on this date in 1989 had 100% cover by the following August (Fig. 5). The bluegrass seeded on this date was very slow to fill in and had substantial weed infestation, but eventually produced an acceptable turf.

What to do now?

As of Oct. 26, I would not recommend seeding opting instead for sodding. Sod can be used successfully during almost any time of the year and is the best way to minimize erosion. Sod laid during the winter will not root significantly until spring, so plan on irrigating the area in spring. Another risk with sod is that it might dessicate during the winter with prolonged cold temperatures and dry winds. Be sure to water the sod thoroughly immediately after laying and occasionally during the winter if there we have an open, windy winter.

On non-erodable areas, wait until after Thanksgiving to dormant seed Kentucky bluegrass, tall fescue or perennial ryegrass. Turfgrass seeded at this time will not germinate until soil temperatures warm up next spring. This technique has been successful on relatively flat areas, but should be avoided on sloped areas prone to erosion. To help reduce erosion on moderately sloped sights, use straw with a tackifier, or other commercially available erosion control nets or blankets. Dormant seeding can be done anytime from Thanksgiving through March or April as long as the soil is dry enough to prepare a seedbed. As with seeding at other times of the year, a starter fertilizer is important, but it should be applied in the spring shortly after germination when the seedlings can use the fertilizer.

Figure 1. Establishment of Sep. 1 and Oct. 1 seedings in Dec. following seeding. Values are averaged over 1990 and 1991 data.

Figure 2. Establishment of perennial ryegrass when seeded at various times throughout the year. Establishment was measured in the August following establishment (1991).

Figure 3. Establishment of fall-, dormant- and spring-seedings as measured in the August following seeding. Values are averaged over 1990 and 1991 data.

Figure 4. Weed infestation in Kentucky bluegrass seeded at various times throughout the year. Weed cover was measured in the August following establishment (1990 & 1991).

Figure 5. Establishment of Kentucky bluegrass seeded in Oct. 1989 and rated through Aug. 1990.