Investigating dormant seeding as an approach to establish lawns in Minnesota

Fri, 10/06/2023 - 08:26

By Andrew Hollman

a straw seeding blanket in spring with grass germinating — Figure 1. Fine fescue seedlings emerging through germination blanket at dormant seeded plot at the Bell Museum, St. Paul MN on 4/11/23.

In the fall of 2022, a dormant seeding demonstration of 15 plots was planted south of TROE just before a predicted snowfall event and stretch of cold weather. The 2022/2023 winter was unusual with an early season snowfall on top of soils that were still quite warm. Frequent snowfall events in the Twin Cities kept a frost layer from developing in the soils until nearly the end of winter and at that point it did not last long. The snow at the demonstration area was completely melted by April 9, 2023 and on April 11, 2023 there was visible germination in the fine fescue plots (Figure 1). Along with the different species and mixtures of turfgrass, the area was also split to show the effect of covering the dormant seeding with germination/erosion control blankets compared to just raking the seed into the bare soil. Part of each plot was also seeded into an existing perennial ryegrass turf that was sprayed with glyphosate after seeding was done (Figure 2). Although the perennial ryegrass was only sprayed a few days before it was covered with snow, the area was completely dead and covered with snow mold mycelium in spring. The density of this layer and how matted it was to the soil surface led to concern on whether grass seedlings would be able to break through it.

three plots in strips labeled A, B, and C — Figure 2. Turfgrass dormant seeding under germination blankets, in bare soil and into perennial ryegrass that was sprayed after seeding at the Turfgrass Research Outreach and Education Center (TROE) on the University of Minnesota St. Paul Campus on 4/12/23 (A=blanket, B=bare soil, C=dead grass).

turfgrass research plots covered with seeding blankets in spring with seedlings emerging — Figure 3. Dormant seeding demonstration plots on 5/1/23 (A=blanket, B=bare soil, C=dead grass).

A bigger concern for the newly emerging seedlings was the unseasonably warm weather and high winds that followed the snow melt. With four days over 80°F and steady winds with gusts over 20 mph, the bare soil area without blankets dried out on the surface and had fewer visible seedlings. It is likely that the light color of the germination blankets and dead turf helped reflect some solar radiation and also protected the soils from strong winds. Being so early in the season, no irrigation was available but the silt loam soil on the site has good water holding capacity and seedlings continued to emerge through both the blanketed areas and dead grass areas. After a week the heat wave ended with rain and cooler temperatures. By May 1st germination was evident in all of the species in the areas covered with the germination blankets (Figure 3). One week later (Figure 4) the plots under the germination blankets continued to improve, the success of the bare soil area wasn’t very good for most species, and the dead grass areas showed more seedling emergence.

turfgrass research plots in spring with some plots having more seedling germination than others — Figure 4. Dormant seeding demonstration plots on 5/8/23 show the effect of germination blankets versus bare soil (A=blanket, B=bare soil, C=dead grass).

a bee lawn with turfgrass and flowering plants — Figure 5. Bee lawn dormant seeding plot on 6/29/23 showing the successful establishment of creeping thyme, self-heal and dutch white clover along with fine fescue.

As the summer progressed the plots continued to fill in. Supplemental irrigation and fertilizer were applied to the entire area to aid in the establishment of the grasses. The need for these applications was most evident in the Kentucky bluegrass and perennial ryegrass plots. The bee lawn plot had successfully established dutch white clover and self-heal within the fine fescue turf and proceeded to bloom in its first season (Figure 5). Creeping thyme was also part of the bee lawn mixture but plants were only found in the dead grass area and they have not yet bloomed; this aligns with our previous observations that this species take more than a year to establish well. Heat and drought continued from mid-August through mid-September. With these conditions the differences in the species became quite evident (Figure 6). The perennial ryegrass showed visible signs of drought stress and was covered in orange pustules from crown rust (Puccinia coronata). Kentucky bluegrass plot also showed signs of rust while the tall fescue plot between them stayed green and disease free. The fine fescue plots and mixtures also looked good during this drought period but did display some damage from traffic (Figure 7). Two weeks later, cooler temperatures and nearly 3 inches of rain led to relief from the drought stress and growth out of the rust diseases (Figure 8).

turfgrass research plots in spring with varying stages of growth — Figure 6. Dormant seeding demonstration plots on 9/13/23 showing the effects of low rainfall and high temperatures on the different species (A=blanket, B=bare soil, C=dead grass).

turfgrass research plots showing damage from mowing traffic — Figure 7. Dormant seeding demonstration plots 9/13/23 showing the fine fescue plots and the effect of traffic during periods of drought and high temperatures.

turfgrass research plots in fall where many of the plots are filled in — Figure 8. Dormant seeding demonstration plots on 9/27/23 after nearly 3 inches of rainfall and cooler fall temperatures (A=blanket, B=bare soil, C=dead grass).

These demonstration plots showed that all of the cool season lawn grasses used in Minnesota can be established by dormant seeding. Differences in the coverage and growth of seedlings showed the benefit of erosion control blankets for successful establishment on bare soil sites. Dormant seeding into a dead turf stand provided adequate seed protection in the spring. We still need to answer a few questions about dormant seeding:

Will late season application of glyphosate always lead to turfgrass death in the spring?
Does the germination blanket inhibit the germination of some bee lawn species?
Is there a quick growing annual crop that could be planted as a nurse crop to eliminate the need for germination blankets or herbicide application?
How long will it take to transition to a lower input species if dormant seeding into an existing Kentucky bluegrass lawn?

With the recent unpredictability of temperatures and rainfall during the late summer and early fall planting time period, dormant seeding might be a good option for those looking to limit the need for irrigation during lawn establishment.