Flowering plant research is headquartered at the Horticulture Research and Extension Center in Olathe, KS with other trial sites in Wichita, Hays, and Colby. These sites encompass two USDA cold hardiness zones (5,6) and two American Horticulture Society heat tolerance zones (7,8). All varieties on the list grow well across the state, east to west and north to south.
Plants are rated for vigor, defined as how fast and how strong they grow and how much substance they have. They are also rated on floriferousness, or total overall visual impact of the flower display. The number of flowers, size of flowers, and how they are borne on the plant are important. Flowers that hang down with backs showing are not as pretty as those presented in profile. Ideally, flowers should tilt up to greet onlookers. On plants where the foliar display is paramount, the floriferousness rating is adapted to take into account the color and visual impact of the leaves, not flowers. The Prairie Star list is now divided into two sections to accommodate the influx of new additions with excellent "foliagiferousness."
Both vigor and floriferousness are rated on a scale of 1 to 7, with 1 being almost dead or no flowers, 4 being acceptable, and 7 excellent. All plants on the Prairie Star list have scored a 6 or higher for vigor and floriferousness combined, at all trial sites for at least 2 years. Plant height and width measurements are taken from a mature plant in mid-August.
Flowering plant varieties in research trials are submitted by or collected from plant breeders and distributors from around the world. All varieties on the list are available from retail garden centers or mail-order plant companies. However, the list contains many varieties - no greenhouse, garden center, or nursery is likely to carry them all. The Prairie Star list is not a commercial brand or product line. Gardeners should look for the specific variety on the list (i.e. not generic "Petunias" but "Supertunia Vista Bubblegum Petunia"). Plants at garden centers may or may not be labeled Prairie Star, so take the list to shop for specific varieties.