Tropicanna cannas and other tender rhizomes, bulbs, corms and tubers can be overwintered with a minimal amount of fuss.
If you live in a climate the doesn’t have winter frosts or freezes (generally zones 7-11), you can leave them in the ground over the winter. To give them a boost, you can cut them back to about 6-8 inches during the winter and they’ll reward you with a healthy regrowth.
If you live in a cooler climate, before a hard, killing frost but after a light frost has turned the leaves dark, cut the tops off to about 4 inches from the base of the plant.
Free your rhizomes from the soil . . .
There’s a good chance that your Tropicanna cannas were reproducing over the summer, so if they’re in a container, you can gently dump the entire container out onto a tarp and carefully separate the canna rhizomes from the rest of the soil/plants. If they’re in the ground, be careful to start digging at least a foot away from the stalk to avoid cutting new growth.
From here you’ll have a few options. We’ve heard of good results with all of these methods, so it’s really your choice.
The lazy gardener’s next step . . .
The easiest way is to overwinter Tropicannas is to carefully brush/knock off as much soil as possible (remember to cut the tops off to about 4″ before trying to do anything more.) . If the remaining soil is very wet, let the rhizomes/soil dry out for a day or so. If they’re only slightly damp, you can put them into large trash bags. Poke a few holes in the bags and fold over the top, allowing some air to be able to flow in and out. Place the bags in a dark cool place – preferably one that stays between 45 – 55° throughout the winter. Check the bags every once in a while. If any of the rhizomes start to shrivel you can spritz a bit of water into the bag. If any are rotted or soggy, remove them and allow more air into the bags.
This video from the University of Illinois’s Extension Service shows just how easy this method is.
For those with more time on your hands . . .
After cutting the tops off and extracting the rhizomes from the pot (not always an easy task, as they grow quite a bit over summer), hose off all the excess soil and allow to dry completely. The rhizomes can then be wrapped in newspaper and stored in a bulb crate, cardboard box or paper bag, separated and covered by clean dry shavings, peat moss, perlite, or sand.
Regardless of which method you use, remember, if the rhizomes get too cold, they could rot. When stored too warm, they may grow prematurely which is not as much of a problem.
For more tips about overwintering and storing other types of tender bulbs, read this great post on About.com by Marie Innotti.
Spring planning and planting . . .
Next spring replant your cannas outdoors again. To get a jump on the growing season, you can pot up cannas indoors four to eight weeks prior to the last day of frost in your area. This way, they’ll already be good-sized plants when you plant them out for the summer growing season – either into large containers or in the ground.
Before planting, cut off any dead tops and divide large rhizomes by carefully pulling apart. You can even cut them apart using a clean, sharp knife. Plant the rhizomes 4-6″ deep and 18-24″ apart, remembering that they’ll continue to grow over the summer. After an initial soaking, don’t keep the soil too wet. Once they sprout you can go back to watering more frequently.