Seed Mix Establishment: Site Preparation Options

PREPARING THE SITE
To prepare a site for planting, you must first eliminate the existing vegetation, which may consist of perennial weeds, annual weeds, or both. Existing weeds will compete with prairie seeds for nutrients, moisture and sunlight. Although it is nearly impossible to remove all annual weed seeds from the seed bank stored in the soil, it is crucial to kill and/or remove perennial weeds and rhizomes before planting. Perennial weeds such as Quackgrass, Bromegrass, Canada Thistle, Canada Goldenrod and Clover can inhibit the growth and development of your prairie. Eliminating all perennial weeds prior to seeding is essential to success with your prairie. Site preparation options may vary according to the vegetation type that you are converting to a prairie planting and include the methods which are outlined here:

OPTIONS FOR PREPARING AN EXISTING LAWN SITE
1.  Smothering OPTION

  • Cover the site with either black plastic, old carpet, plywood or a thick layer of leaves or newspapers, held in place to prevent blowing.  (We do not recommend covering newspapers with topsoil, as the soil may contain numerous weeds).
  • Leave in place for a full growing season and remove in the fall or the following spring.
  • Prepare bed.

2.  Sod Cutting OPTION – for lawns free of perennial weeds only.

  • Remove the top two to three inches of grass and soil with roots using a sod cutter.
  • Prepare bed.

3.  Cultivating OPTION

  • Cultivate with rototiller, cultivator or similar tool. Do this two to three times at one week intervals to kill the lawn. Remove clumps of sod & thatch to create a smooth seed bed.
  • If perennial weeds are present in the lawn, cultivate for a full growing season, at intervals of every two to three weeks. This should kill both the lawn and the perennial weeds.
  • Prepare seed bed after all weeds have been killed.

4.  Herbiciding OPTION

  • Apply a Glyphosate herbicide when the lawn is actively growing (in fall or spring). Weedy lawns may need further applications of herbicide.
  • When the grass has turned brown, turn the soil under to prepare for seeding. Remove clumps of sod & thatch to create a smooth seed bed.

OPTIONS FOR PREPARING A NEWLY DISTURBED,
OR NEW CONSTRUCTION SITE

Areas of bare soil resulting from recent construction may appear weed free at first, but all soils contain an astonishing array of weed seeds that will re-sprout and grow and may out-compete your seed mix. The best approach is to wait and see what comes up and then kill any weeds prior to installing a seed mix, rather than seeding into a recently cleared/disturbed site. To prepare a new construction site or newly disturbed area, first, allow the weeds to emerge and grow up to a height of one foot. Once the area has sprouted and grown to reveal the existing weed bank, choose a preparation method from the “Options for Preparing an Old Field Site” options below — ­either Cultivating or Herbiciding. If the existing weed bank is not addressed you will not have a suitable, clean seed bed for the germination and growth of your seed mix.

OPTIONS FOR PREPARING AN OLD FIELD SITE
Fields that have been abandoned and allowed to grow up into grasses and weeds require at least a full year for proper site preparation. Completing two years of weed control is even better, due to the presence of established perennial weeds and weed seeds in the soil. Please do not rush your site preparation if you are planting an old field. It cannot be over-emphasized that you need to eliminate all weeds before seeding. There are two ways you may go about it:

1.  Cultivating  OPTION

  • Mow and rake or burn off the existing vegetation to the ground in late fall or early spring.
  • Cultivate to a depth of four to five inches every two to three weeks from spring through fall.
  • Before planting, make sure all the existing weeds have been killed. This procedure may require two consecutive years of cultivating to kill pernicious, noxious weeds.
  • Plant in fall or the following spring into a prepared bed.

2.  Herbiciding OPTION

  • Mow and rake or burn the existing vegetation to the ground in late fall or early spring.
  • Apply a Glyphosate herbicide three times throughout the growing season at six to eight week intervals (mid-spring, midsummer, early fall), when plants are green and actively growing.
  • If perennial weeds are still present on the site after a full year of herbiciding, do not seed. Leave the soil undisturbed over winter, and apply one more herbicide treatment in late spring of the following year to kill any remaining weeds. (If in doubt that this additional application is sufficient, wait, spray for a second year at six to eight week intervals and seed in the fall.)
  • When all the vegetation is dead, work the ground to prepare a seed bed (see specific planting instructions in “Preparing the Final Seed Bed”).

OPTIONS FOR PREPARING EXISTING FIELDS OF CORN,
SOYBEANS OR SMALL GRAINS
Corn and grain fields can easily be converted to prairie immediately after harvest or the following spring. Before planting into corn fields, test the soil for persistent agri-chemicals such as Atrazine. If present, Atrazine can kill germinating prairie wildflower seedlings! To determine if it is present in your soil, perform this simple test: Grow ten oat seeds in a pot with the cornfield soil. In another pot, grow ten oat seeds in potting soil, or unaffected garden soil (this is your experimental “control”). When the oats reach a height of about four inches, those growing in Atrazine-laden soil will stop growing and turn yellow. Oats growing in untreated soil will continue to grow, without yellowing. Compare the oats growing in the cornfield soil with those in the untreated “control” soil to make sure that any positive results for Atrazine are not shared by the oats in the untreated soil. If Atrazine is present, we recommend allowing the site to sit for one to two years before you plant your prairie. If unsure of the site’s herbicide history, contact the farmer who owned the land; they must keep records of Atrazine use.

1.  Cultivating  OPTION

  • Mow and rake or burn off the existing vegetation to
    the ground in late fall or early spring.
  • Cultivate to a depth of four to five inches every two to three weeks from spring through fall.
  • Before planting, make sure all the existing weeds have
    been killed.
  • Plant in fall or the following spring into a prepared
    bed.

2.  No-till OPTION, Fall or Spring Seeding

  • If planting in fall, the seed can be scattered into the dead vegetation without tilling as long as exposed soil is visible below the vegetation. The seed will work its way down into the soil over winter through freeze and thaw cycles, and germinate the following spring. This method is a “dormant seeding.” Fall dormant seedings typically result in higher germination of wildflower seeds, but produce lower germination of warm season prairie grasses. Spring seedings result in higher germination of warm season prairie grasses, and somewhat lower germination of certain wildflowers.
  • Prairies can be planted in spring using a No-Till Drill or Slit Seeder (Tye, Truax etc). This equipment inserts the seed 1/4 to 1/2 inches into the soil and is suitable for planting large sites.

3.  Herbiciding OPTION

  • Spring:  Spray once in mid to late spring, this will kill annual weeds. Wait 10 days or until vegetation is brown then plant into a prepared seedbed.
  • If problem perennial weeds such as quackgrass, bromegrass, Canada Thistle, and clover are present, treat the field with a Glyphosate three times throughout one full growing season, at six to eight week intervals (same as “Options for Preparing an Old Field Site” above).
  • Fall:  After crop is harvested, if weedy vegetation is present and is still actively growing, spray with Glyphosate, wait 10 days and plant into a prepared seedbed.
  • If the crop is removed late in the season, wait until spring to spray the field when weeds are again green and actively growing. If problem perennial weeds such as Quackgrass, Bromegrass, Canada Thistle, and Clover are present, treat with Glyphosate three times throughout one full growing season, at six to eight week intervals, (same as “Options for Preparing an Old Field Site,” above).

Up next: Preparing the Final Seed Bed


Designed for areas of 1000 square feet or more, we’ve designed 24 native seed mixes for virtually any soil or condition:  http://www.prairienursery.com/store/seed-mixes


Establishing a native plant seed mix is a long-term investment in your landscape, which
requires careful planning. When questions arise a one-on-one conversation may be the best way to get the information you need. Don’t hesitate to call us at 800-476-9453, Mon. – Fri., 8am – 5pm, CST. Or, email us at cs@prairienursery.com. We are happy to discuss individual complexities in order to make your planting a success.