Selecting the proper species for any given planting site is critical. This will ensure that each species in the seed mix has the best chance to establish and persist in the stand. There are a number of species selection criteria listed below that we have incorporated into the Tallgrass Prairie Seed Calculator to give you the very best seed mix for your location and soils. Individual species are automatically selected in the calculator based on your input selections - county of the planting (99 counties to choose from), soil moisture (dry, dry-mesic, mesic, wet-mesic or wet), and cost factor (premium or economy).

Species Presence - The calculator only includes tallgrass prairie species native to Iowa’s tallgrass prairies. Inclusion of species in the calculator have been verified through herbarium specimens, present in prairie remnants, and/or included in vascular plant surveys from plant taxonomists past and present (Eilers and Roosa 1994, Christiansen and Muller 1999). It can be argued that a species presence/absence in any given location in Iowa cannot ever be truly be known because the tallgrass prairie biome was nearly eliminated over a hundred years ago. However, we have taken the ‘do no harm’ stand and rely on verified information rather than taking a chance on introducing a species into an area that it doesn’t belong.

Geographic Distribution - Consideration for historic distribution for each species within Iowa is in the calculator. If a species was verified in a given county (home county), the seed calculator will recommend this species be planted in the home county and only in counties immediately adjacent to the home county. We believe that this is a good compromise between keeping the historic distribution of a given species intact without extending it too far out of its range.

Species Habitat Preference - The calculator ensures that each species recommended in the seed mix matches the soil moisture regime of the planting site. If a given species prefers wet soils it is recommended for planting sites with wet soils, mesic species for mesic soils, dry species for dry soils, etc. Not matching a species soil moisture requirements to the planting site will result in poor plant establishment and the species will not persist in the stand.

Appropriate seed sources - Nearly all species in the calculator have Iowa ‘yellow tag’ seed commercially available. Iowa ‘yellow tag’ seed has been certified as to having its origins from seed collected in Iowa prairie remnants. There are a few species that do not have Iowa ‘yellow tag’ seed commercially available that the calculator recommends. In these cases, it will be up to the seed buyer to decide whether or not to purchase and use this seed for their prairie projects. New species will be added to the seed calculator when they become commercially available and when they also meet the criteria for inclusion that we have described in the criteria for species selection section.

Plant Guilds - Every recommended seed mix includes species from all plant guilds that occur in diverse remnant prairies. These guilds include: warm-season grasses, cool-season grasses, sedges, legume forbs, and non-legume forbs. Having multiple species from all plant guilds in the stand makes it more resistant to weed invasion (Naeem et al. 2000). A diverse prairie seed mix should contain the minimum number of species listed in Table 1. Field observations confirm that all plant guilds are included in high quality prairie remnants in Iowa.

Flowering Time - Flowering will occur throughout the growing season. Every recommended seed mix has species that flower in late spring, summer, and in early fall. This will provide continuous floral resources for pollinators like the Monarch butterfly. Field observations confirm that high quality prairie remnants in Iowa have floral resources that span the entire growing season.

Life Span - Every recommended seed mix includes annuals, biennials, short and long-lived perennials. It is important to include annuals and biennials to stabilize bare soil, reduce weed competition in early establishment, and to recolonize the site in the event of a disturbance. Perennials provide long-term diversity and stability. Field observations confirm that high quality prairie remnants in Iowa include species with all life spans.