"Approximately thirty of the species are cultivated. Cultivated varieties mainly represent five species: C. vernus, C. chrysanthus, C. flavus, C. sieberi and C. tommasinianus. Among the first flowers to bloom in spring, crocuses are popular with gardeners. Their flowering time varies from the late winter C. tommasinianus to the later large hybridized and selected Giant "Dutch crocuses" (C. vernus). Crocus flowers and leaves are protected from frost by a waxy cuticle; in areas where snow and frost occasionally occur in the early spring, it is not uncommon to see early-flowering crocus blooming through a light late snowfall.

Most crocus species and hybrids should be planted in a sunny position, in gritty, well-drained soil, although a few prefer shadier sites in moist soil. Some are suitable for naturalising in grass. The corms should be planted about 3 to 4 cm deep; in heavy soils a quantity of sharp grit should be worked in to improve drainage.

Some crocuses, especially C. tommasinianus and its selected forms and hybrids (such as 'Whitewell Purple' and 'Ruby Giant'), seed prolifically and are ideal for naturalising. They can, however, become weeds in rock gardens, where they will often appear in the middle of choice, mat-forming alpine plants and can be difficult to remove."

Taken from wikipedia's page at: http://en.wikipedia.org/wiki/C...