Canna lilies are one of the easiest tropical plants for the gardener to overwinter – which is exceptionally convenient as they are also one of the most versatile plants in the summer garden. With large, often colorful leaves, and unusual, re-blooming flowers in bright happy colors, they add a lush, exotic look to garden beds and containers, re-energize a hot and humid summer garden, and are even happy in boggy ponds or in container water features on a partly-shaded patio.
You don’t need a greenhouse to overwinter cannas. The thick, fleshy rhizomes can be easily stored in a cool basement, garage or cellar in total darkness – no heat lamps, timers or expensive lighting systems required. So, if you’ve worked hard to put together a beautiful collection of tropical cannas this season and hate to see them killed by a cold winter, follow the easy steps below to keep them blooming and reproducing in your garden for many seasons to come.
Rhizomes are underground stems that store food and produce shoots and roots.
Why should I overwinter canna lilies?
Cannas spread vigorously, forming clumps of thick, fleshy rhizomes held close to the soil surface. That’s a lot of plant material to simply throw away when temperatures hit the freezing mark! Especially when they are easy to dig, easier to store, and doing so over the winter months allows you to cost-effectively increase their presence in your garden. You can build your cultivar collection over time and still have plenty to share with other gardeners.
You don’t need a greenhouse to consider overwintering cannas. In fact, even if you do have a greenhouse, it’s much easier to store them in a garage, basement, crawl space or unheated spare room. Don’t have any of those places? You might have a friend who doesn’t mind housing a plastic bag of maintenance-free rhizomes in their cellar – particularly when you share a few in the spring!
Using an unheated cold frame in the early spring months can help you get the foliage going earlier in the season, but even if you don’t, you’ll find your cannas can’t wait to get started again once the temperatures warm.
When should I dig canna lilies for overwintering?
While cannas are sending tropical foliage skyward during the growing season, they are also spreading into the soil, creating shallowly-rooted clumps of thick but brittle rhizomes. If you are north of Zone 8, mid-autumn and frosty temperatures will signal that it’s time to dig those rhizomes for winter storage.
The autumn garden is a busy one, so don’t add to your workload too soon. Let the frost visibly blacken canna foliage before you dig – usually in mid-to-late fall. The trick is to get them out of the ground before temperatures substantially drop and the ground freezes. Waiting also allows you to get the most from your cannas – they will continue to grow and produce flowers often late into the autumn, adding much to the fall garden.
Gardeners in Zone 7 who apply a thick layer of mulch (6-8 inch) to clumps of cannas after cutting down the stems stand a good chance of overwintering them 'in situ' – particularly with straight species such as Canna indica. If you have lots and can ‘afford’ to lose a few, experiment!
in situ is a Latin term which means ‘in its original place’
How do I dig canna lilies for overwintering?
Use a digging fork to gently lever the clump out of the ground. As cannas are shallowly rooted, this will be easier than you think! If you are storing cannas grown in containers, you can either store the cannas, container and all, or remove the clump from the container and proceed in the same way as with garden-grown cannas, depending upon your storage space. Container grown cannas will need to be replanted in fresh soil next season for best results.
Separate the rhizomes with your hands. Be gentle, but do not worry if they break. The fleshy roots will dry up during storage, so again, handle carefully but don’t worry too much about breakage.
If they have been in garden soil, do not wash the rhizomes, as doing so invites disease problems during storage. Instead, remove the soil and lightly brush them off. However if they were located in a boggy condition or in a water feature (cannas make great pond plants!), cleaning off the muck and detritus from a long season is advised.
Cut off the old foliage stalks 1-2 inches above the rhizome with a clean knife. Then, carefully inspect the rhizomes for rot or animal damage and discard those with signs of disease. If it’s a large rhizome, you can use a clean knife to cut off rotten or damaged areas to clean, white flesh. Remember, different cultivars of canna look the same naked. If you’re digging several types at the same time, put them into large, labelled trugs (even if it’s just a scrap piece of paper thrown in with them). Before you store them later, you can do a better job of labelling.
How do I store canna lilies for overwintering?
Now comes the easiest part of all – preparing them for storage. Traditional methods advocate placing them in containers or bags filled with slightly dampened peat moss or wood shavings, but for those short on time or either of those materials, cannas can also be overwintered simply by placing the sorted rhizomes into heavy duty garbage bags and storing in the correct conditions (see below). The garbage bags will help maintain a good level of humidity without adding extra moisture.
However you decide to store them, make sure to label bags or pots of rhizomes carefully with tags. You can also use a Sharpie to write directly on the rhizome itself. You’ll thank yourself when spring comes and those rhizomes start sprouting.
Where do I store canna lilies for overwintering?
Find a cool, dark space that stays above freezing but below 55 throughout the winter. Non-fluctuating temperatures are best as they prevent early sprouting. Some great storage places to consider are:
- Unfinished basements
- Unheated garages
- Deep cold frames
Avoid Outbuildings (barns, potting sheds, etc. as they often tend to fall below freezing in the deep winter.
Directly after storing the rhizomes, and particularly during a warmer autumn, you may see a certain amount of early re-sprouting. It’s safe to ignore this but means your temperatures need to be a bit cooler. If plants are continuing to re-sprout adjust the temperatures or store somewhere cooler, as this will eventually exhaust the rhizome’s resources.
When can I replant canna lilies in the garden?
As temperatures increase and spring returns, re-inspect your rhizomes – throw away any that are rotten or diseased and if some are beginning to sprout in storage, lightly dampen with water to replenish resources. Cannas are tropical warm season plants. They will not only be harmed by planting them in the garden too early, but they will not grow vigorously until temperatures are warmer.
At this point you have two choices: Either wait for the right time in the garden to plant, or force them into earlier strong growth using a cold frame or greenhouse. Whichever route you take, plant the rhizomes 3-4 inches deep in rich soil approximately 1’ apart with a small amount of balanced fertilizer. Lay the rhizome horizontally in the soil with any bud swellings (eyes) or new shoots pointing up. Water well.
Natural timing for canna rhizomes
Keep your storage areas cool, and when all danger of frost has past, re-plant outside or in containers in rich soil with a small amount of balanced fertilizer. Foliage will take a while to re-sprout, but will be ready for your summer garden. If you are planting in a water feature, make sure to cover the soil of the container with at least 2 inches of pea gravel to keep soil firmly in the pot.
Forced timing for canna rhizomes
Approximately 4-5 weeks before the last frost, replant the rhizomes in small temporary containers (perhaps 2 per gallon pot), with fresh soil and a small amount of balanced fertilizer. Keep them protected in cold frames or an unheated greenhouse with plenty of light. As temperatures naturally warm outside, you will begin to see sprouting above the soil line. Keep them well watered and do not forget to check daytime temperatures in your cold frame or greenhouse. Temperatures can rise quickly and damage the emerging foliage.
When all danger of frost is past, replant the cannas in containers or garden beds at the same soil level they were in the pots. They should be well-leafed out and ready for the season ahead!
Handy tips for making the process even easier:
- If you are using a garage or other cluttered area, start to set aside space in late summer in preparation.
- Look for wheeled multi-level carts at yard sales so you can store all your dormant plants in one place and easily move them out of the way if needed.
- Convert a raised vegetable bed into a mini-hoophouse using flexible PVC pipe and 6ml plastic in early spring so you can bring your cannas into growth early.
- If, after many winters, you have a lot of a certain cultivar and you are in Zone 7, consider overwintering some of the rhizomes in situ with a heavy layer of mulch (6-8”) over the top – especially if they are in a free-draining, sandy soil. Dig others as an insurance policy against a bad winter.