Hardy in U.S. Department of Agriculture plant hardiness zones 6 through 8, saffron crocus (Crocus sativus) is a fall-blooming plant from which saffron spice is collected. Grown from an underground root structure called a corm, it prefers a well-draining, rich soil bed located in part shade to full sun. If you properly care for your saffron crocus plants, in time, they will reward you with more and more prolific flowers. In three or four years, though, they can multiply so much that flower production decreases. This indicates that division is necessary to maintain a thriving crocus bed.
Cut the saffron crocus foliage about 2 or 3 inches above ground -- so you can still locate the corms -- when it withers and dies back in fall.
Dig into the soil with a garden fork, which is less likely to harm the corms, around the cut foliage to remove the corms from the ground. Expect them to be about 2 to 6 inches below the soil surface, because they can settle and grow deeper than the original 2- to 4-inch planting depth.
Brush the soil off the corms and rinse them under water. Lay them out to dry in a dry, airy location out of direct sunlight for two to three weeks.
Examine the corms to look for smaller corms, called cormels, growing on the outside of the main corm. Grab these with your fingers and pull them off to divide them from the parent corms; no cutting is necessary. Some of the smallest corms might fall off when handling the dry corms; you can still plant them all.
Replant all the corms and cormels in the garden 2 to 4 inches deep and 3 to 4 inches apart in well-draining soil that is located in partial shade to full sun. Plant the smaller cormels closer to the surface and closer together than the main parent corms that are larger in size.