Cannas are typically grown in the outdoors. However, many gardeners remove their canna rhizomes from winter storage in March and begin to grow them indoors in pots. They are then replanted outdoors later in the spring to be enjoyed a bit sooner than cannas that were planted directly outdoors. While not common, you can also grow and keep your cannas in pots, if desired.
Choose a canna plant. Some varieties can grow to be very tall. In fact, the flower spike of Canna altensteinii can reach as high as 8 feet. Large canna varieties may not be suitable for growing in pots, especially if you want to keep the cannas in pots indefinitely. Some varieties, like the Canna warscewiczii, grow to be only 2 feet tall and may be a better choice for growing in pots.
Select a pot. If you are planning to keep your cannas planted in pots, you will need a large, heavy container, even if you are growing a smaller variety. Pots made with clay or ceramic and are at least 18 inches deep would work for many cannas. They must have drainage holes on the bottom for proper drainage. If you are planning on replanting your cannas outdoors, then smaller plastic containers would suffice.
Plant the canna rhizomes 3 to 4 inches deep with the buds (or eyes) facing up in high-quality all-purpose potting soil. If you are planning on keeping your cannas in pots, then only plant one rhizome per pot since they need to be planted about 1 ½ to 3 feet apart. The plant will become fuller and more lush over the years. However, if you are going to transplant them outside, they can be planted a couple inches from one another.
Backfill the soil and pack it down firmly. Water well until the water comes out the bottom of the pot. Pack down the soil again. Then, set the pot in a sunny area and keep the soil evenly moist.
Replant--if desired--the cannas outside at the same depth once spring arrives and the ground has warmed up.