Crocuses are usually spring and summer blooming plants, however, there are some varieties that are fall blooming. Crocuses are actually members of the iris family and have solid root structures that are often called bulbs. They are in fact not true bulbs, but corms. Crocuses are typically grown in USDA zones 3 to 9.
Plant crocus bulbs (corms) in well draining soil. If your soil has puddles that remain on top 5 hours after a hard rain, it is not well draining. Till the top 12 inches of your soil and mix in several inches of humus, such as peat moss or compost.
Plant in the fall, before the ground freezes. The bulbs will grow fleshy roots during the winter months, which is essential to water absorption in the growing season (spring to fall). Plant bulb--with the tips facing up--4-6 inches deep and 4-6 inches apart.
Fertilize in the fall after planting and once a year in the fall thereafter. Use a soluble 10-10-10 fertilizer and only a small amount, less than a teaspoon per plant.
Keep the soil evenly moist from spring until fall. Do not over water, which will cause the bulbs to rot.
Let the foliage turn brown or yellow. Do not cut it after the crocuses are done blooming and the foliage is still green. If you don't like the way this looks, plant other flowers mixed in with your spring and summer blooming crocuses, such as vincas or fall blooming crocuses.
Cover the planting site with a couple inches mulch in colder zones in the fall. This will help keep the bulbs warmer during the winter months. You can also use mulch during the growing season to help retain water and maintain soil temperatures.