In many ways, the preparation of the site is much like the methods involved in vegetable gardening. If the site has a bluegrass or fescue sod, this should be removed by taking off the sod with a sod removal machine or by using a nonselective herbicide to kill the grass. If you decide to use an herbicide, a 1% solution of Roundup applied as a foliar spray will kill most grasses and broadleaf plants present on the site. Once the sod is dead, it should still be removed because it will interfere with the growth of prairie seedlings and the design of the planting.
Once the sod has been removed, the soil should be cultivated to prepare the site for planting. It is not necessary to cultivate deep into the soil. This procedure may cause problems later because the soil may not be firm enough. Use a tiller and cultivate the upper six to eight inches of soil. The soil should not be cultivated intensively. That would create a loose planting bed for the prairie plants, and could result in poor plant survival because the soil will be too loose around the root systems.
Many sites will be enhanced by the construction of a dirt mound, thereby creating variations in the topography of the site. This can be accomplished by bringing soil in from another part of the property or by purchasing soil. If the soil comes from a site other than your property, make sure that it is very similar to your soil. Also make sure that it does not contain the seeds of aggressive exotic plants such as sweet clover or teasel which could threaten the success of your planting.
Once the soil has been placed on the site, it should be shaped according to the design plans that you have made. The mound should be shaped so that it appears to be a natural part of the planting. This will make the planting much more aesthetically pleasing to you and to other observers of the site.
Some sites, due to construction activities, may have a very tight clay soil which will need some improvements in richness and porosity before planting the prairie garden. Incorporate sand and peat or a good topsoil into these sites using a garden tiller. Work the site until these materials are thoroughly incorporated into the soil. The amount used will depend upon local soil conditions.