Dormant seeding: The story continues

By Andrew Hollman

The 2023 MN State Fair once again brought on a plethora of questions about lawns from fairgoers. Bee lawns and weed control were popular but water use was an underlying theme for many. For some, too much irrigation was needed to keep their lawn green. For others, their lawn did poorly even when it was watered. For many, they didn’t irrigate and their lawn was dead or infested with crabgrass. Most of these attendees were open to the idea of planting species other than Kentucky bluegrass, such as fine fescue or tall fescue, which would use less water or be able to avoid the drought better. Typically in Minnesota the late summer (late August to early September) is the ideal time to seed cool-season turfgrasses. Soil temperatures are warm, rains usually become more consistent, and the air temperature begins to cool. Unfortunately, September 1, 2023 was in the middle of our second drought of the year, with high air temperatures and no foreseeable rainfall in the forecast. Trying to establish turfgrass with those conditions would have been difficult for anyone without an automatic irrigation system; not to mention, watering that much does not send a good message during a drought about responsible water use. For most of these situations I recommended that the sites be dormant seeded, a technique that doesn’t require immediate watering.

turfgrass research plots where several of the plots are dying and yellowing due to herbicide application
Figure 1. Plots of perennial ryegrass were sprayed with glyphosate at different timings. Image taken 11.14.23.

From the previous work at our research center, we knew that the common cool-season turfgrass species can be established when dormant seeded. An interesting observation from this project was that dormant seeding into a living lawn and then immediately killing the lawn with herbicide worked really well. Because the weather conditions for the winter of 2022/2023 were unique, we wanted to explore this approach further. Would spraying the existing turfgrass with an herbicide after dormant seeding lead to a successful dormant seeding or should the turf be killed in late October before the dormant seeding? To help answer this question a trial was initiated in the fall of 2023 into a stand of perennial ryegrass. Glyphosate was applied in either late October or after dormant seeding on the 20th of November when soil temperatures dropped below 40F (Figure 1). The study includes separate plots for hard fescue, tall fescue and Kentucky bluegrass. Through this coming spring and into summer we will assess the success of converting an existing stand to a different species and whether spraying after dormant seeding (Figure 2) successfully kills the existing grass.

turfgrass research plots in the late fall where the grass is not actively growing
Figure 2. Plots that were dormant seeded on 11.20.23 into an existing perennial ryegrass turf stand sprayed with glyphosate A) before seeding 10.25.23, B) after dormant seeding 11.20.23 or C) not sprayed. Image taken on 1.25.24. 

Dormant seeding into a weed-free turfgrass area may be an option for some, but what about the people who had lawns that had been completely killed and overtaken by crabgrass in 2023? Many of these consumers had a desire for a lawn that required very little supplemental irrigation for maintenance or establishment. Dormant seeding can often achieve this, but a bigger question is: how do we deal with a site where there has been a history of crabgrass? To examine this, we dormant seeded a trial into a site where crabgrass had dominated in 2023 (Figure 3). We seeded individual plots with a Kentucky bluegrass blend, a fine fescue mixture or a tall fescue blend. In the spring we will test multiple pre-emergent herbicides and application timings to see if we can find a combination that will be safe on the cool season grasses and limit the emergence of crabgrass.  We also have untreated controls so we can see whether these different mixtures may vary in their natural ability to keep the crabgrass from germinating.

turfgrass research plots where most turfgrass has been killed
Figure 3. Dead area where different turfgrass mixtures or blends were dormant seeded on 11.20.23 so different control methods for crabgrass could be tested in the spring of 2024.

With these two trials we hope to add some new methods backed up by solid research on how to convert an existing lawn through dormant seeding.