Planting a prairie garden

1. Site selection:

Prairie plants grow best in full sun and in open spaces. When selecting a site, look for areas with the maximum sun exposure with minimal root competition from trees. Ash, basswood, and maple trees provide more competition for prairie plants because they have many surface roots which compete for water and nutrients. Prairie plants often are more compatible with bur or white oak.

Knowing your soil type and surface drainage is quite important when selecting plants for your prairie. Native prairie soils vary greatly in composition, from dry, gravelly, sandy soils which hold little moisture to silty or heavy clay soils that can hold excessive water. Standing water on a site or water that does not drain from a 1' deep hole within 24 hours are indicators of wet and poorly drained soils. Knowing the soil drainage of your site is really more critical than taking a soil test which is typically done in planting a garden. Although you may have a soil test done, (soil test information is available from your county extension agent or from the University of Minnesota soil testing labs*) it is not critical in establishing a successful prairie garden. Understanding the drainage and sun/shade exposure of your site is essential for selecting plants that thrive in your location.

Determine if there are weed ordinances in your city. These ordinances were originally designed to keep yards more attractive and to control the spread of noxious weeds by keeping lawns cut to a certain height. Ordinances vary from one city to another, so call your city government to find out the specifics on the weed ordinances in your community. Consider using some "elements of care" such as mowed eDGes, signs, bird houses, eDGing fences, etc., near your prairie to show the area is meant to be there.

Also, prairies can be fire hazards during dry weather. Leave at least 20 feet of conventional lawn or noncombustible surface between the prairie and buildings or any other combustible items.

2. Site preparation:

The first step in preparing the site for a prairie garden is removing all existing vegetation. If you try to scatter seeds or put young plants into existing vegetation, you will have a very low likelihood of success. Maximize your success by reducing the existing plant competition.

There are three commonly used procedures to establish a prairie in an existing lawn or area of other vegetation. The first method is to put a dark plastic sheet, tarp, or pieces of plywood over the grass for at least two months before you begin planting. This kills the grass, making it much easier to remove, although tough perennial weeds, such as thistles and quackgrass can survive. Once the vegetation is dead, till the area thoroughly. This method often works best when begun in the summer or fall to prepare for a spring planting.

The second procedure is to turn the soil and cultivate the area every few weeks for a complete growing season. Turning the soil brings weed seeds to the surface, and cultivating kills the seeds that have germinated since the soil was last turned. Over time, many of the weed seeds present in the soil will germinate and die. If possible, till to a depth of 12" or more and rake the area to create a uniform fine seedbed.

A third method, and probably the most common method of establishment, involves using a nonselective herbicide containing the active ingredient glyphosate, such as Round Up® or Kleenup®, to kill all existing vegetation. As with all herbicides, be sure to read and follow all label directions. When the vegetation has died in about two weeks, till to a depth of 12" or more. If a slit seeder will be used, tilling may be eliminated and the now dead vegetation can be mowed to a 1"- 2" stubble. This dead mat of roots and sod may actually act as a mulch and prevent excessive weed growth.

3. Plant selection:

Always select plants with the characteristics of your particular site in mind, because plants vary in their tolerance of light and moisture. Include grasses because they provide physical support, weed competition, protection for wildflowers, and a source of food and shelter for birds during the winter. Prairies typically consist of 60% - 80% grasses. A brief list of common prairie plants can be found in Table 1, For a more complete list see Minnesota Extension Service publication Plants in Prairie Communities (FO-3238).

4. Seeds vs. plants:

You can start a prairie from seeds or plants; each has its own benefits. Starting from seed is more economical, but it will take two to five years for the plants to reach full size. Plants are more expensive, but establish quickly and may flower the first year. Also, some species are available only as live plants. You can control placement of plants, and they can easily be planted anytime from spring through fall. "Prairie-in-a-can" mixes are available from a wide variety of sources, but often contain marginally hardy perennial and annual species that don't return in subsequent years. Better results may be achieved by using seed mixes created for your area by local seed dealers. Be sure that any seeds you purchase are packaged for the year that you will sow them.

5. Planting dates:

The best time to direct sow seeds outdoors is after frost and before the heat of summer. For example, in central Minnesota this is between May 20th and June 20th, although seeds can be sown as soon as the soil can be worked. Dormant seeding in the fall, between mid-October and freezing, is another option.

Even seed distribution and good seed-to-soil contact are vital for successful seed germination. Broadcast seed by hand or use a spreader. For small seeds, mix with a bulking agent such as clean sand or dry sawdust for a more uniform seeding. Seed slowly and make passes from two different directions to cover the area completely. Flower seed can be concentrated in high-priority areas or spread evenly throughout the site. Many seeds are very small and should be spread thinly to achieve the best results. Seeding rates vary due to seed size and germination. As a general rule, use 1/2 lb. of grass seed per 1000 square feet, and 2 ounces of wildflower seed per 1000 square feet. ore specific instructions on seeding rates can be obtained from the information provided when purchasing seeds.

Watering after seeding improves germination, but is not essential. Covering with a thin mulch of clean, weed-free straw prevents drying out, reduces exposure to wind and animals, and is important in preventing erosion on slopes. Grouping several plants of the same species together can make a showy display and can increase pollination and seed set.

* Contact the University of Minnesota soil testing labs by phone at 612-625-3101, or by mail at 1529 Gortner Avenue, St. Paul, MN 55108.

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