Rocky Mountain Iris (Missouriensis)

The Rocky Mountain Iris (Missouriensis) is generally described as a perennial forb/herb. This is native to the U.S. (United States) has its most active growth period in the summer . The Rocky Mountain Iris (Missouriensis) has green foliage and inconspicuous purple flowers, with a moderate amount of conspicuous black fruits or seeds. The greatest bloom is usually observed in the spring, with fruit and seed production starting in the summer and continuing until spring. Leaves are not retained year to year. The Rocky Mountain Iris (Missouriensis) has a short life span relative to most other plant species and a rapid growth rate. At maturity, the typical Rocky Mountain Iris (Missouriensis) will reach up to 1 foot high, with a maximum height at 20 years of 1 foot.

The Rocky Mountain Iris (Missouriensis) is easily found in nurseries, garden stores and other plant dealers and distributors. It can be propagated by bare root, bulbs, corms, seed. It has a moderate ability to spread through seed production and the seedlings have high vigor. Note that cold stratification is not required for seed germination and the plant cannot survive exposure to temperatures below -28°F. has low tolerance to drought and restricted water conditions.

Uses of : Landscaping, Medicinal, Culinary, etc.

Warning: Fresh iris roots and rhizomes may be toxic.

Ethnobotanic: Iris makes some of the finest cordage; the fibers are particularly strong and flexible. Iris cordage was used for fishing nets, string, rope, snares, hairnets, and regalia. These fibers are very fine and silky, but surprisingly strong. The threads and cords of this fiber were used to make fishing nets, camping bags and snares for catching deer, birds, and other game. In spite of the tremendous labor of preparing this material, the iris fiber was one of the most generally employed in northwestern California.

Rope was made from fibers, which occur, on the outer margins of iris leaves. Huge bunches of leaves were harvested in the fall and stored until needed. A single silky fiber was taken from each margin of the leaf. None of the other fibers were used. The men always knotted the fishing nets. A deer rope is near 20 feet long with a lasso at one end, and about half an inch in diameter. This loop was set over a deer trail to catch the head or antlers. Within the set loop over the trail was spread a delicate network of the same material to draw in the loop. One Indian stated that it takes nearly six weeks to make a rope twelve feet long.

A poultice of the raw rhizome is especially effective against staph sores. Externally iris rhizomes are successfully used on infected wounds, ulcers, fistulas and to take away freckles. Only the dried iris root or rhizome should be used internally. Iris is active as a cathartic, has a stimulating effect on the production of both pancreatic enzymes and bile, is a strong diuretic, and will stimulate both saliva and sweat. This is a useful medicinal plant but in general should be used with care and preferably in combinations where less energetic plants forming the bulk of a medicinal formula.

Landscaping & Wildlife: The beautiful and variable blossoms lend themselves to landscaping, where they naturalize and require minimal maintenance. Native irises are free flowering, most are long lived, require very little attention, and provide an abundance of seeds. Iris flowers attract both insects and hummingbirds.

Invasive Potential: Western blue flag is considered a noxious weed in pastures, because leaves are unpalatable and bitter.

General Characteristics

General: Iris Family (Iridaceae). Western blue flag is a perennial herb, usually evergreen and growing from a creeping, tuberous rhizome. Rhizomes on blue flag are between 20-30 mm in diameter, quite large for a native iris. The leaves are long and linear with parallel venation, 3-9 mm wide, and sometimes purplish. Stems are 2-5 dm and sometimes branched. Blossoms of Iris missouriensis are pale lilac to whitish with lilac-purple veins.

Required Growing Conditions

For current distribution, please consult the Plant Profile page for this species on the PLANTS Web site.

Cultivation and Care

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.

General Upkeep and Control

In autumn old leaves should be removed from the center of large clumps, the foliage cut back, and a mulch applied, especially if the irises are being naturalized in a semi-dry area. Traditional resource management included harvesting huge bunches of iris leaves in the fall, and storing these leaves until needed. The fibers are then harvested from the leaves. This naturally accomplished the pruning and mulching that modern horticulturists practice to maintain iris beds.

The PCI borer (Amphipoea americana var. pacifica ) and iris borer (in the eastern U.S.) are serious pests of iris. The PCI borer stays in the rhizome through the winter, then metamorphoses, coming out sometime in the spring as a nocturnal moth. Controlling the moth, to prevent it from laying its eggs on the iris, will control the borer. However, it is recommended to dig infested plant out entirely, put it a plastic bag, and then place it in the garbage can to avoid contamination of other plants.

Milkweed (Asclepias species) and dogbane (Apocynum cannibinum) were traditionally burned by native people in the fall to maintain vigorous plant production, to stimulate plant growth, to optimize long and abundant fiber production from leaves and stalks, and to stimulate seed production. It is probable that iris was burned for the same reasons.

Plant Basics
Growth Rate Rapid
General Type Forb/herb
Growth Period Summer
Growth Duration Perennial
Lifespan Short
Plant Nativity Native to U.S.
Commercial Availability Routinely Available
Physical Characteristics
Bloom Period Spring
Displays Fall Colors No
Shape/Growth Form Colonizing
Drought Tolerance Low
Shade Tolerance Intermediate
Height When Mature 1
Vegetative Spread Rapid
Flower Color Purple
Flower Conspicuousness Yes
Fruit/Seed Abundance Medium
Fruit/Seed Seasonality Summer Spring
Seed Spread Rate Moderate
Gardening Characteristics
Propagations (Ways to Grow) Bare Root, Bulbs, Corms, Seed
Moisture Requirements High
Cold Stratification Required No
Minimum Temperature -28
Soil Depth for Roots 6
Toxic to Nearby Plants No
Toxic to Livestock No
After-Harvest Regrowth Rate Rapid
After-Harvest Resprout Ability No
Responds to Coppicing No
Growth Requirements
pH Range 7–8.5 pH
Precipitation Range 24–24 inches/yr
Planting Density 1000–40000 indiv./acre
Soil Textures Coarse, Fine, Medium
Soil Depth for Roots 6
Minimum Frost-Free Days 115 day(s)
Salinity Tolerance None
CaCO3 Tolerance High
Sustainability & Use
Leaf Retention No
Palatability Low
Fire Resistant No
Causes Livestock Bloating None

Source: USDA, NRCS, PLANTS Database,
National Plant Data Center, Baton Rouge, LA 70874-4490 USA