The native irises are excellent in shade situations, even dense shade of walls and fences (Schmidt 1980). They will tolerate sun for most of the day in mild areas, and should have afternoon shade and ample water in the interior regions. These plants are intolerant of frequent summer water; they should not be planted near lawns or other moisture-loving plants. However, Iris missouriensis does need irrigation to get established. Fertilization increases biomass and seed production. Irises start growing with the first cool weather and fall rains, reaching the height of their growth in spring and early summer. This iris is rhizomatous, forms clumps, and propagates readily from plant division in fall or winter.
Propagation by Plant Division: In the wild, Iris missouriensis tends to produce only a small, dry rhizome with stringy roots. Vigorous garden or greenhouse plants produce firm, white, growing roots especially during the winter and spring growing seasons, allowing easy division of clumps. Remove a new rhizome fan with fleshy roots and set it in a prepared site. Keep the newly planted rhizome watered so that it is moist, and provide shade for a few days if the plant is placed in full sun. Frequent division appears to keep the plants vigorous, as well as being the best method of increasing the supply.
Propagation by Seed: Iris seeds are easily collected from the large capsules. These capsules turn from green to brown and open at the top when ripe. Care must be taken when handling seeds because they split very rapidly; two days after ripening the seed has spilled out. Collect capsules carefully to avoid spilling seeds; each capsule has from 20 to 80 seeds. Seeds should be stored in paper envelopes at room temperature until they are planted. The seeds of all species will keep up to 10 years at room temperature.
Plant seeds in 6-inch pots, using a combination of leaf mold and peat moss. Cover seeds with 1/2 inch of same material. Any good potting soil that's acidic is good for seed germination. Keep soil moist but not wet. After planting, over-winter the pots outdoors in November or December. They will come up in 2-3 months, depending on the weather. Germination increases the second year, because there's always a percentage of hard seeds that won't germinate the first year. Delaying germination until the next year, to increase the probability for good weather conditions and optimize germination success enhances seedling survival.
Plant the seedlings outdoors in May, when the young plants are usually 3 to 6 inches tall or even taller. Plants are likely to require watering the first year during roots establishment. Plant from 6 inches to one-foot spacing. If a natural look is desired, scatter and clump the plantings. Plants will begin to bloom by their second year if growth has been continuous.
Direct seeding is possible in places that can be left undisturbed, as among shrubs, or among low perennials where the seedlings can be sheltered. If planting seeds in the ground, autumn is the best time for seeding; germination begins in two or three months and often continues beyond that time. A friable seed mixture of sand, loam, and either peat or screened leaf mold is best, covering the seed with sphagnum moss to aid in preventing damping-off of seedlings.
