To propagate Colchicum, the most common method is to divide the corms during their dormant period in the summer by carefully separating smaller offsets from the main corm and replanting them individually; this is best done when the plant is overcrowded and needs thinning out every few years;. 

Key points about propagating Colchicum:

Division time: Always divide Colchicum corms when they are dormant, typically in mid-summer after the foliage has died back. 

How to divide: Gently dig up the clump, brush off excess soil, and carefully separate smaller corms (offsets) from the main corm. 

Repotting: Plant the divided corms in fresh, well-draining soil at a depth of about 3-6 inches, spacing them according to the variety. 

Seed propagation: While possible, propagating Colchicum from seed is less common as it can take several years for plants grown from seed to flower.