The canna lily's flowers resemble true lilies, but this plant belongs to the Cannaceae plant family. The genus Canna contains 19 species, with many hybrid cultivars in existence. You can collect seeds from your canna and grow new plants using that method, but because so many varieties are hybrids, you won't always get the same plant as the parent. Dividing the underground bulb, or tuber, is a more successful way to propagate cannas.
Wait until your canna stops its summer blooming. Then dig up the entire plant, being careful not to damage the tuberous clumps from which the foliage grows.
Separate the tubers by gently pulling them apart. Each piece must have an "eye," much like a potato, in order for it to grow.
Prepare 4-inch nursery pots with drainage holes by filling them about half full with standard potting soil. Then set one tuber in each pot and fill it to within 1/2 inch of the top with more potting soil.
Water your pots thoroughly and then cover them with a sheet of glass. Keep your covered pots in an area that receives filtered sunlight because intensely hot sun can cause the tubers to cook under the glass. Remove the glass every day to water your canna tubers.
Remove the sheet of glass when you first see the tubers sending up growth. Allow the plant to grow in its pot until spring, after the threat of frost has passed. Then you can transplant your young cannas to the garden. Plant them 1 foot apart and about 5 inches deep.