Establishment Of Grass And Wildflower Mixes For Low-Maintenance Landscapes

By the third year, plants representing less than half of the forb species in the mixes had been found. Weed competition was more severe on the mesic site, and fewer species from the seed mixes were detected in the second year. By the third year, a greater proportion of the forb species in mixes became established on the mesic than on the xeric site. The only exceptions were Silphium species, which were found on the xeric but not on the mesic site.

INTRODUCTION. Many popular authors have recommended the use of native grasses and wildflowers as an alternative to turf in more "natural-looking" landscapes (Shirley, 1994; and Smith, 1980; Stein, 1994; Wilson, 1992). These landscapes are often described as "meadows" or "prairies," suggesting analogies with ecosystems that may have existed locally before urban development. There is extensive literature on ecological restoration, particularly for prairie and savanna ecosystems (Packard and Mutel, 1997). However, there is little information comparing different approaches to establishment of similar plants in residential landscapes.

In ecological restoration, the conservation of local genotypes is always a priority. Such material may not be available to property owners who are interested in establishing a small meadow or prairie area. It is likely that they will use commercially available plants or seeds from more remote sources. This project set out to evaluate some of the native grass and wildflower mixes available commercially.

MATERIALS AND METHODS. Ten seed mixes were obtained from Prairie Moon Nursery (Winona, Minn. 55987) and Lofts Seed Inc. (Somerset, N.J. 08873). The Prairie Moon mixes were strictly U.S. native prairie species (and mostly Ohio natives). Of the Lofts Seed mixes, only ‘Reclaim Native Grass’ was entirely of native species; the others included nonnatives. The forb seeds in the Prairie Moon mixes were subjected to moist stratification at 4 degrees Celsius for 60 days before sowing. Each mix was used to seed two plots (50 m2) at each of two locations - the "xeric site" is in The Ohio State University’s (OSU) Chadwick Arboretum, alongside SR 315 in Columbus, Ohio; the "mesic site" is adjacent to a small lake in the OSU Turfgrass Science Facility.

Each site was prepared by application of glyphosate herbicide at the recommended rate about six weeks before planting followed by shallow (7.5 cm) cultivation. Seed was mixed with vermiculite as a carrier and broadcast at the same rate recommended by the suppliers. Most of the seed was sown before plots were raked lightly to bury it; the small seeds in the Prairie Moon mixes were sown after raking. The seed bed on the xeric site was rolled after sowing on June 13, 1997, but the mesic sit was too wet for this operation when it was sown on the same date.

The sites were mown at a 10-cm height three times in the 1997 season and again in April 1998 to suppress annual weeds. Flowering heads of biennial weeds, such as Arctium minus, Brasica spp., Daucus carota and Rumex cripus, were removed by hand. In July 1998 and 1999, each plot was surveyed for presence of species that were in the original seed mixes, and in 1999, the area of each plot occupied by these species was estimated.

RESULTS. The Prairie Moon seed mixes included annual ryegrass and a sterile wheat cultivar as nurse crops. These established quickly so that the plots seeded with these mixtures looked cleaner than those with the Lofts Seed mixes in the first year. Apart from the nurse crops and some annual species, such as Chamaecrista fasciculata and Rudeckia hirta, it was difficult to find species represented in the seed mixes. Annual weeds such as Chenpodium album and Setaria viridis were conspicuous, and periodic mowing was used to minimize their competition with the slower growing species in the seed mixes.

In 1998, more species from the seed mixes were identified on the xeric site than in corresponding plots on the mesic site (see Table 1 below). Showy species, such as Gaillardia pulchella, Coreopsis lanceolata and Hesperis matrionalis in the ‘Songbird’ mix and Rudbeckia spp. in the Prairie Moon mixes, were more conspicuous on the xeric than on the mesic site. At the end of the 1998 season, it was apparent that other slower-growing species had not established on the xeric site.

In 1999, species that had not been observed in earlier years were found, particularly on the mesic site. A few species, notably Chamaecrista fasciculata and Astragalus canadensis, had disappeared from both sites. The number of species and the area that they occupied was generally higher on the mesic site than in corresponding plots on the xeric site (see Table 1 below). An exception was that Silphium spp. were better represented on the xeric than on the mesic site. However, most of the forb species in the mixes have not been observed so far. The species in ‘Reclaim Native Grass’ established on both sites and achieved good ground cover (see Table 1 below). The same species - Andropogon geradii, Bouteloua curtipendula, Panicum virgatum, Sorghastrum nutans and Schizachyrium scoparium - were included in one or more of the Prairie Moon mixes. However, they were absent or poorly established in areas seeded with these mixes, particularly on the xeric site. The Prairie Moon shortgrass mixes were poorly established on one or the other site.

DISCUSSION. The seed mixes tested contained mainly perennial grasses and forbs that take several years to become established. In the early years, they are in competition with annual and biennial weeds that are slowly excluded as the perennials achieve 100 percent cover. Many of the perennial grasses and forbs can grow quite rapidly in the absence of competition. In other experiments with transplanted seedlings, they have filled areas and flowered in a single season. Transplanting is more labor-intensive than seeding, and this limits the areas that can be established. For large areas, seeding may be the only feasible method of establishment; weeds may be the most obvious plants in seeded areas in the first year, and the perennials will only begin to flower in the second year.

The inclusion of annuals and fast-maturing perennials in mixes makes them attractive in the early stages of establishment but may add to the competitive pressure on slower-growing perennials. Grasses seem to be particularly vulnerable to competition early in establishment, as shown by their failure on the xeric site in the prairie mixes. Mixtures based on short grasses, such as Schizachyrium scoparium and Bouteloua curtipendula, seem to be particularly difficult to establish and appear to be more important to match the species to the moisture status of the site than for tallgrass mixes.

The value of having a large number of forb species in a seed mix can be questioned when most do not become established. It could be argued that different species could succeed on different sites, but there was limited evidence of this for the two sites in this study. Part of the interest in the more complex seed mixtures is the element of surprise when a species appears in the second or third year after seeding. Legume species as a group either were not seen or failed to persist for more than a year. Special steps may be necessary to get them established.

In view of these difficulties with forbs and forb-rich mixes and the success with the tallgrass mix on both sites, it may be preferable to establish a grass matrix and then look for gaps where forbs can be introduced by seeding or transplanting. Periodic burning in the fall or spring is advocated for natural prairie and savanna areas, in order to exclude weeds and maintain a desirable balance of grasses and forbs. Burning may not be possible in many residential locations and further research is necessary to determine alternate management practices to maintain small areas of this kind.

More information about this project can be accessed online (Knee, Jourdan, and Rhodus, 1998) at: www.hcs.ohio-state.edu/sense/sense1.html.

ACKNOWLEDGEMENTS. Thanks are due to Lofts Seed, Inc., and Prairie Moon Nursery for the donation of seeds.

LITERATURE CITED:

Knee, M. Jourdan, P., and Rhodus T.M. 1998. Sense of Place: Native plants for locally appropriate landscapes. www.hcs.ohio-state.edu/sense/sense1.html.

Packard, S. and Mutel, C.F. Eds. 1997. The Tallgrass Restoration Handbook for Prairies, Savannas, and Woodlands. Washington, D.C.: Island Press.

Shirley, S. 1994. Restoring the Tallgrass Prairie: An Illustrated Manual for Iowa and the Upper Midwest. Iowa City: University of Iowa Press.

Smith, J.R. and Smith, B.S. 1980. The Prairie Garden. Madison, Wisc.: University of Wisconsin Press.

Stein, S. 1994. Noah’s Garden: Restoring the Ecology of Our Own Backyards. Boston: Houghton Mifflin.

Wilson, J. 1992. Landscaping with Wildflowers. Boston: Houghton Mifflin.