by David Trinklein University of Missouri Division of Plant
As the gardening season begins to wane, a plant with crocus-like flowers comes into bloom, seemingly out of nowhere. The result is an unexpected appearance of spring in the fall of the year.
The plant in question is Colchicum autumnale, commonly known as autumn crocus or meadow saffron. Its flowers arise from the soil without leaves and often achieve a height of between 8 to 10 inches. Although the flower resembles that of a crocus in shape, autumn crocus is a member of the Liliaceae (Lily) family of plants while crocus belongs to the iris (Iridaceae) family.
Autumn crocus often is planted just before it blooms. In fact, it can even be planted while in full bloom. The large bulb-like corms the plant produces contains sufficient nutrients and water to complete the flowering process without being in soil. At times in the past, gardeners would purchase the corms and allow them to flower indoors and then plant them in the garden. This practice, however, did result in some drying of the corm while indoors resulting in flowers that did not last very long after being planted outdoors.
The leaves of autumn crocus are produced in the fall of the year, after flowering has occurred. However, they do not make significant growth until the following spring. By late spring, the strap-like leaves which are about 12 inches long and one inch wide, wither and die. No further above-ground evidence of the plant exists until its flowers appear in September.
Autumn crocus tolerates a wide array of exposures from full sun to partial shade. It prefers a well-drained garden loam; poor drainage or very tight soils can weaken plants and induce bulb rot. Plant the corms three to four inches deep in soil that has been amended with a general purpose fertilizer such as 5-10-5.
Rock gardens, raised beds or sites under trees are ideal locations for autumn crocus. It can tolerate light shade from deciduous trees but avoid planting it under trees that cast dense shade. Much of the leaf growth of autumn crocus occurs in early spring before trees have leafed out fully.
There are several varieties of autumn crocus available. ‘Lilac Wonder’ and ‘The Giant’ are two of the most spectacular because of their large flower size. Flower color is violet-mauve and rosy-lilac, respectively. ‘Waterlily’ is a double-flowered pink variety also available. Although not as large as the previously-mentioned varieties, it is quite attractive.
There are no major pests of autumn crocus, but a word of caution must be given. The corms of autumn crocus are highly poisonous because of a compound they produce called colchicine. The latter has seen limited medicinal use to treat conditions such as gout, certain types of cancer, irritable bowel syndrome and pericarditis. It also is used in plant breeding to induce polyploidy in plant species such as daylily.
Because of its highly toxic nature, autumn crocus should not be planted in gardens frequented by unattended children or pets.
In addition to autumn crocus, there are several species of true crocus that also flower in the fall, rather than in the spring. Like autumn crocus, their corms need soil with excellent drainage. Failure to provide the latter results in general decline and ultimate loss of the plant. Loose, somewhat sandy, soil ideally fits their preference. Again, these crocuses are good candidates for rock gardens, raised beds or under trees that cast light shade.
Most of the true crocuses that flower in autumn bear flowers that only rise about six inches above the soil. Additionally, their foliage is much smaller and more grass-like when compared to Colchicum autumnale.
Crocus sativus, commonly known as saffron crocus, is probably the best-known of the true crocuses that flower in the fall. In addition to being a highly attractive flower, it is the source saffron. The latter is widely known as the most expensive spice in the world. Saffron is derived from the deep-orange stigmas of the flowers. There are only three stigmas (also called saffron threads) per flower. Given that it takes about 14,000 threads to produce one ounce of saffron, it is no wonder that saffron is priced and sold by the gram.
Another reliable true crocus that flowers in the fall is Crocus speciosus, also known as Bieberstein’s crocus. It bears attractive flowers that are light purple in color with violet veins. It increases rapidly in the landscape and is a good choice for naturalization.
In both of the above cases, the crocus will flower soon after it is planted. Now is an
ideal time to look for their corms at retail outlets.
Someone once mused, people should plant autumn crocus at least once, if for no other reason than to surprise your neighbor. An under-used fall bloomer, autumn crocus plants are a welcome addition to the usual combination of chrysanthemums and asters used by gardeners to extend color in the garden late into the growing season.