Suddenly Cannas are everywhere. While these tropical perennials were known only from exotic gardening magazines just a few years ago they have gradually come north and are now a popular and exciting addition to our summer gardens and planters. Unfortunately, as a zone 10 plant, the Canna will not survive outdoors in our brisk zone 3 winters. Much like the more familiar dahlia or gladiola, the Canna needs to be treated as a tender bulb.
This may seem odd because Cannas are not a bulb at all but just a large tropical plant with a very fleshy tuberous root. This root is what most gardeners started with this spring in their balcony planters or outdoor garden displays. It's the part to preserve if they are kept over winter for growing again next spring.
Canna tubers sell for only a few dollars each for the unrooted tubers in early spring. Most people won't be too concerned if they lose this $2.00 dollar investment by letting the plant die outside this fall. If the plant was purchased as a rooted plant in a one gallon pot - and especially if they have interesting variegated foliage - the initial cost may have been twenty to thirty dollars each. At this price it makes sense to consider saving these tropical giants over the winter. It may also be hard to get the unusual red or yellow striped forms of canna when you want them - another reason many people will choose to bring their saved plants back to life next spring. Whether its the cost factor or just the flexibility of having a reliable supply on hand many people have no experience with cannas so are asking the same questions I had for Sanna Barlem, the ornamentals gardener at the Calgary Zoo.
Barlem started with cannas at the zoo three years ago with 12 half-gallon pots. In the Dorothy Harvie gardens this year a massive display over 20 metres long is packed with 300 plants all generated from the original dozen pots. The secret to this rapid propagation is relatively easy.
Cannas are tropical but their dormant period can be somewhat cool as long as it is dry. Barlem offered the following steps to success:
Dig plants with a garden fork after the first hard frost.
Shake the excess soil off the roots and find a warm dry spot to allow the leafy plants to die back completely. Barlem uses a greenhouse bench but a warm dry garage or attic will also work.
Trim top growth away from the tubers once the leaves are dry and loose.
Store dry tubers on top of dry peatmoss in a 5-10 degree C spot (a cold storage area will work but it doesn't have to be too cool as long as it is dry).
Plant tubers in pots as early as March or put them directly outdoors in the spring garden after danger of heavy frost is past.
Although Barlem didn't share any fear of this rapid multiplier I might add one additional sanity tip at this time. Cannas seem akin to another favorite fast growing tropical - the zucchini. If you decide to accept this overwintering mission, be prepared to line up your adoptive homes in advance.
ABOUT THE AUTHOR:
Donna Balzer is a Calgary based horticulture consultant and garden writer. She is the author of Gardening for Goofs and The Prairie Rock Garden and may be reached for consultations at 403-233-8999 or via her web page at http://www.gardenguru.net