September 17, 2010
Bermudagrass Overseeding Tips
For those of you managing bermudagrass sites that require overseeding, it’s time to start planning for that process. Although a dense stand of perennial ryegrass can look strikingly good in the winter and spring, a patchy stand of ryegrass usually looks worse than if no overseeding were done at all. Unfortunately, I’ve learned this first-hand from conducting a couple not-so-successful overseeding experiments in my front lawn. So, here are a few tips that will help ensure a successful overseeding experience for those of you who are <*ahem*> fortunate enough to go through this process.
How Much Seed?
When it comes to selecting a perennial ryegrass seeding rate for overseeding bermudagrass, the adage “more is better” bears some truth. Recommended overseeding rates for perennial ryegrass are several times higher than rates recommended for establishing perennial ryegrass as a permanent turf. In a recent overseeding study at Purdue University, significant improvements in perennial ryegrass coverage were observed as the seeding rates increased up to 50 lb. pure live seed / 1000 ft2. As seeding rate increased beyond 50 lb. / 1000 ft2, improvements in ryegrass coverage were less noticeable.
Improve Coverage with Split Applications
Perennial ryegrass coverage can also be improved by splitting the seed application dates. In the same overseeding study at Purdue University, perennial ryegrass that was seeded at a 1/4 rate in 4 sequential applications (10 days apart) had 50% greater coverage than when all of the seed was applied at once.
Improve Spring Transition with Tetraploid Perennial Ryegrass
In recent years turfgrass breeders have developed some cultivars specifically for the overseeding market. One in particular that has performed well in University of Arkansas trials is a tetraploid (doubled chromosomes) perennial ryegrass cultivar, ‘T3’. ‘T3’ has good turf quality, but has poor heat tolerance and persists into the summer much less than other perennial ryegrass cultivars (Fig. 1).
Sneak in a Soil Cultivation
We have done some research looking at pre-plant cultivation effects (core-aerification, verticutting) on overseeding establishment and have seen some pretty favorable results from core-aerification prior to seeding. Although the effects on overseeding establishment rates have been inconsistent (never negative), the upside is that you can core-aerify your bermudagrass at a time that might be more favorable than mid-summer. The quick-establishing ryegrass will cover the scars of aerification in a few weeks.
Figure 1. Dormant bermudagrass plots in the fall with perennial ryegrass that has persisted following overseeding the previous season. The tetraploid (chromosomes doubled) perennial ryegrass cultivar, ‘T3’ is less heat tolerant than standard (diploid) perennial ryegrass cultivars.
Doug Karcher and Mike Richardson