Cannas have underground root structures that are commonly referred to as bulbs and are often sold as bulbs. Technically, canna bulbs are not "true" bulbs; they are rhizomes. No matter what you call them, you need to dig up canna bulbs each year so that they can survive and be enjoyed again the next year. Wait until the canna foliage turns brown or a frost kills your cannas.
Cut the canna foliage back so that about 4 inches are left above the ground.
Dig up the bulbs using a garden fork, trowel or shovel. On all sides of the plant, dig about 6 inches deep and then pull down on the handle to lift the bulb out of the soil.
Shake off most of the excess soil, but leave a bit on. Then, lay the bulbs out in a dry area (not in the sun) on some newspaper for several hours before storing.
Pack the bulbs in a single layer in a cardboard box, separated and covered by clean peat moss, perlite or sand. The rhizomes should not touch each other. If your storage area is very dry, enclose them in a plastic bag. Punch holes in the bag so air can circulate.
Keep them in a dry, dark place around 50 degrees until it is time to plant them.