Written by: UMN Turfgrass Science group
The turfgrass science team annually spends the unofficial last 12 days of summer at the Minnesota State Fair answering questions about lawns. A common refrain from fair-goers is that their lawn is full of weeds, but they don’t want to use any chemicals to fix the problem.
Seeding is an often-overlooked practice to solve many problems found in lawns. This doesn’t always mean starting from scratch and re-seeding but can also utilize different overseeding methods to incorporate new plants into an existing lawn. With this idea, we are specifically interested in using overseeding practices to renovate lawns that are infested with annual grassy weeds like crabgrass (Digitaria spp.).
While typical turfgrass overseeding can be done during the early fall months when growing conditions are still good, fall droughts have made this more difficult in recent years. In Minnesota and other areas within the Upper Midwest we can instead dormant seed (e.g. frost seed) when soil temperatures are below 40°F. With this method, the seeds will germinate in spring when the temperatures warm up and moisture is usually more prevalent. In areas that have warmer winters than in Minnesota, dormant seeding is less successful because warmer temperatures during the winter can cause the seed to germinate too early, making it subject to damage if cold weather returns.
We have tested dormant seeding with a number of different lawn grasses and tall fescue (Schedonorus arundinaceus) appears to work best with this method in Saint Paul. Tall fescue is a cool-season turfgrass species with a deeper root system than other commonly used cool-season turfgrasses, which allows it to access water deeper in the soil and stay healthier longer during a drought. Success with tall fescues made us wonder if dormant seeding could be a chemical-free way to improve a lawn that was infested with crabgrass-a common problem in Minnesota..
To test this idea out, we established an experiment in 2023 in which turfgrasses were dormant seeded directly into a 100% crabgrass lawn to see if the turfgrasses could outcompete the crabgrass the following years. For this experiment we compared tall fescue to other commonly-used lawn grasses: Kentucky bluegrass (Poa pratensis), and fine fescue (Festuca spp). eeds were applied with a drop spreader calibrated to the recommended rate for each species directly into dead crabgrass on November 20th, 2023 (Figure 1, above). No plot or soil preparation was done before or after seeding so that we could test the effectiveness of just seeding. In March of 2024 germination was observed and rainfall was the sole method of irrigation for the plots. Since these were newly seeded plots, an application of starter fertilizer was applied at the end of April.
By mid-May the tall fescue plots were easily distinguished from the other turfgrass species and just a couple weeks later the crabgrass population increased over the trial area (Figure 2).
Data were collected to determine percentage cover of the turfgrasses seeded, cover of crabgrass (or other annual grassy weeds), and cover of broadleaf weeds using a grid intersect method during the summer and once in the fall in 2024 and 2025.
The results of this experiment showed that tall fescue could effectively reduce crabgrass populations when dormant seeded the year prior (Figure 3, below). Tall fescue plants established quicker than both Kentucky bluegrass and fine fescues in early 2024, leading to a significant reduction in the percentage of crabgrass and broadleaf weeds throughout the year.
By the beginning of October, the decline of the crabgrass clearly showed how successful the tall fescue dormant seeding was with minimal inputs (Figure 4). In 2025, little to no crabgrass could be counted in plots dormant seeded with tall fescue, while crabgrass was still present during the summer in both fine fescue and Kentucky bluegrass plots (Figure 3, below). We repeated the trial again starting in fall 2024, and the results have been very similar.
What does this mean for those Minnesotans who want to be rid of unsightly crabgrass without having to spray herbicides? Good news! We found that a lawn consisting of 100% crabgrass could be converted to 100% tall fescue by dormant seeding tall fescue two years in a row. The other turfgrasses evaluated were not as successful; this was likely due to the slower establishment rates of these species. The dormant seeding method we used was very simple and required no preparation, and would be easier for many householders.
This research was conducted by Andrew Hollman and supported by the Minnesota Turf and Grounds Foundation (MTGF). Come see us at the State Fair this year! Location in the education building. We'd love to help you!