During September a plant with crocus-like blossoms comes into bloom. This plant is the colchicum, sometimes called meadow saffron. The flowers rise from the soil without leaves and may be as high as 8 to 10 inches above the soil. Although the flower shape is similar to crocus, they are members of the lily family while true crocus belong to the iris family of plants.
While colchicums are normally planted just before they bloom, they can even be planted while they are blooming. The large storage bulb that they produce contains enough nutrients and water to complete flowering without being in soil. It was once a novelty to purchase the bulbs and allow them to flower indoors and plant them in the garden only after flowering was completed. Some drying of the bulbs occurs during this process indoors and flowers do not last as long as outdoors. If this is done, prompt planting after flowering is important to insure good growth in spring and flowering next fall.
The leaves of colchicum are produced in fall after flowering has been completed. However, they do not grow significantly until next spring. By late spring the leaves, which are fairly coarse and about a foot tall, will collapse and die. There will then be no further above ground evidence that the plant exists until the flowers appear in September.
Several varieties of colchicum are available. Among the most spectacular are Lilac Wonder and The Giant which have the largest flowers in violet-mauve and rosy-lilac, respectively. A double-flowered pink called Waterlily is also available. It is not quite as large or as vigorous as the previous varieties, but very attractive. A white form also exists. It is smaller and the least vigorous of the group, but the smaller flower size is closer to that of true crocus.
The large bulbs, or tubers, of colchicum need a well-drained location. They are tolerant of many soil types, but poor drainage or very tight soils can weaken them or help induce bulb rots. Rock gardens, raised beds or sites under trees are suitable. They will not grow in dense shade but can tolerate light shade from deciduous trees. Much of their leaf growth occurs in early spring before most trees have leafed out fully. There are no major pests of colchicums, but a word of caution should be given – the bulbs are poisonous. These are the plants from which the material used in plant breeding called colchicine is extracted.
There are species of true crocus that flower in the fall rather than in the spring. Like the colchicums, these bulbs (or corms) need excellent drainage, and failure to provide it insures decline, rots, and eventual loss of them. Loose soil, somewhat sandy, fits their needs best. They are also suitable for rock gardens, raised beds or similar locations under trees without dense shade.
Autumn crocus are not as large as colchicums. The flowers rise only about 6 inches from the soil and the foliage is more grass like. It is produced to some extent after flowering, but makes most growth early next spring. Flowering in autumn crocus is later than in colchicum. Most flowering of fall crocus takes place in October. One of the best and most durable fall crocus species for our climate is Crocus speciosus. The flowers are light purple with violet veining.
Probably the best known of the autumn crocus is the saffron crocus, Crocus sativus which has light purple flowers. This is the plant from which the spice saffron is obtained. It may also be grown in our gardens, but is quite sensitive about drainage. The deep orange-red stigmata which are harvested from the flower to obtain the saffron are also very attractive.
Colchicums are suitable for use among low ground covers such as vinca where they can remain undisturbed and protected. The true autumn crocus are more delicate and need to be in a rock garden or bed with smaller plants. They cannot compete well with larger plants.