Blue flag (Iris versicolor) is a native perennial plant of common occurrence in swamps and marshy situations throughout the eastern half of the United States. The underground stem (rhizome) and roots are the parts of the plant used medicinally.

Blue flag responds readily to cultivation when placed in a rich, moist, and rather heavy soil. It is readily propagated from divisions of old plants, which may be set 1 foot apart in rows spaced conveniently for cultivation. If the plants are set in August or September, the crop may be harvested about, the last of October in the following year. The roots may be turned out with a deep-running plow, and after being thoroughly washed and the larger clusters broken up they should be thoroughly dried. Artificial drying at low heat is usually desirable.

Yields at the rate of 3 or 4 tons of dried root per acre have been obtained from small plats. The prewar price paid to collectors varied from year to year and usually ranged from 5 to 10 cents a pound. The price in June, 1920, was 35 cents a pound. This crop does not appear to be very promising, owing to the relatively small demand for the root