Arboretum News

Native Grass Restoration

Arboretum research seeks to restore prairie dropseed, a crucial source of food and shelter for at least five species of native butterflies.

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Prairie dropseed research site at Lake Tamarack. Photo courtesy of Katherine Brewer.

by Katherine Brewer, Graduate Assistant, and Mary H. Meyer, Professor Emeritus

While walking through the Ornamental Grass Collection at the Minnesota Landscape Arboretum, you may be drawn to prairie dropseed (Sporobolus heterolepis). It has graceful arching leaves and a unique fragrance that attracts attention. Prairie dropseed is a beautiful ornamental grass, but it is also an important North American native prairie grass. Prairie dropseed is a crucial source of food and shelter for at least five species of native butterflies including the federally endangered Poweshiek skipperling (Oarisma poweshiek). However, you are more likely to find it in a garden than a prairie. Prairie dropseed is often not included in restoration plantings, because it is slow to germinate and does not compete well as a young seedling. Since it is often not included in restoration plantings, we are researching ways to increase establishment and survival of prairie dropseed in prairies that have already begun restoration. This work is supported by the Hope Goddard Iselin Fellowship in Public Horticulture through the Garden Clubs of America.

Mature prairie dropseed plant in the Ornamental Grass Collection. Photo by Mary Meyer.

Prairie dropseed is slow to germinate and vulnerable to competition as a seedling, so why not find a way to bypass that fragile phase? Landscape plugs do exactly that. Plugs are small plants that are grown in a greenhouse or nursery where they are given an ideal environment for germination and protected from competition. These plants then have a leg up when planted in a restoration. We decided to use plugs of prairie dropseed grown in either a traditional commercial peat-based potting mix or in native soil. 

Prairie dropseed started in native soil in the greenhouse. Photo Courtesy of Katherine Brewer.

Native soil is important because many plants, including prairie dropseed, do not exist alone. They partner with beneficial fungi and bacteria that live in the soil. We hypothesized that using native soil would help prairie dropseed plants survive and grow in the restoration. Because the plants were grown in native soil, they were introduced early on to any beneficial fungi or bacteria. We wanted to compare survival and growth of plants grown in native soil against plants grown in commercial peat-based potting mix, because this is what is available to professional restorationists. 

Growing seedlings in native soil was not the only restoration method we tested. We also examined the effect of treating the young plants with hydrogel at planting. Hydrogels are dry crystals that when soaked absorb many times their weight in water. Over time, the water is slowly released. Hydrogels are commonly used in some areas of horticulture, such as nursery production, and have been occasionally used in restoration work. We hypothesized that plants treated with hydrogel would have higher rates of survival and growth than plants not treated.

 Newly planted prairie dropseed plants. Photo courtesy of Katherine Brewer.

To test our hypotheses, we planted 1,000 plants at each of three restored prairies at the Minnesota Landscape Arboretum: the Bennett Johnson Prairie, Spring Peeper Meadow and Lake Tamarack. You may have seen the bright flags marking our research plots while exploring the Arb! At each prairie, we planted plants grown in the native soil and plants grown in potting mix and treated the plants with hydrogel either during planting, or watered the plants in directly after planting. We took survival counts in June and August of 2020 to measure survival through the winter and summer and in August and October, we harvested plants using a bulb planter. We used the bulb planter to remove a core of soil surrounding the plant roots. We then washed all the roots by hand, (a lengthy process!) before drying and weighing the plants. 

This project is ongoing, so right now our results are limited. However, we found that plants planted at Lake Tamarack had higher survival and growth rates than plants grown at either Spring Peeper Meadow or the Bennett Johnson Prairie. We suspect that this is because the surrounding plants are less dense at Lake Tamarack, so competition is lower. This knowledge allowed us to plant a second phase of 350 more plants at Lake Tamarack that are not part of this research project and will not be harvested. We hope these plants will create a permanent population of prairie dropseed at the Arboretum.

Learn more about the benefits of planting prairie dropseed.

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