One of the biggest draws of canna lilies is that they can be grown in just about every USDA hardiness zone, although often as annuals. This means they’re a perfect substitute for valid lily species with a much narrower growth range.
However, as cannas aren’t cold-hardy, it’s essential to know how to properly overwinter them unless you want to start over every year.
If you’re growing your cannas in a container (especially dwarf cannas), you can bring them inside when the temperature cools off.
However, overwintering a canna planted in the ground will require a little extra effort.
This process isn’t as tricky as it sounds, and you will have an easy time keeping your cannas alive for replanting once you know the rules.
How To Overwinter Canna Lilies
While you can grow canna lilies as a perennial in warmer climates, you will need to uproot and store them in the winter in colder zones as annuals.
The process is relatively easy if you follow a few simple rules and can help prevent starting from scratch every year.
Why Canna Rhizomes Are Often Called Bulbs
Canna lilies are rhizomatous, not bulbous plants.
Growers often mistakenly refer to the rhizomes as bulbs because they overwinter similarly.
However, Canna rhizomes are very different from bulbs in structure and growth habits.
This is important when dividing, checking for disease, and planting.
Bulbs have layers like an onion.
They have a generally pointed tip that dictates the direction of planting and tend to be planted deeper than rhizomes.
Meanwhile, rhizomes have a rind and starchy interior, like a potato.
They have eyes, often primarily on the upper side, and grow horizontally in the ground.
#1 – When To Uproot Your Cannas
As a general rule, you’ll need to overwinter your cannas if you live anywhere north of USDA hardiness zone 8, although cutting back and adding a thick layer of mulch can often keep your cannas alive in zone 7b and parts of zone 7a.
We recommend overwintering starting in zone 7a unless you have successfully mulched them in the past.
Also, don’t rush to dig up your canna bulbs, as this will cause more work for you and can also deprive the plant of some stored energy it could be building up.
Instead, watch your cannas as fall hits and look for the first signs of frost damage.
This will usually manifest as wilting of the leaves, with them turning yellow or brown, then black.
When you see this sign, you’ll know the plant is about to die back and has stored as much energy as it can for the winter.
Be sure to dig them up before the ground freezes or it begins snowing, as a complete freeze can kill the rhizome.
#2 – Preparing To Uproot
Begin by cutting the plant back to 2″ to 3″ inches (some prefer to cut cannas back to the ground immediately, but leaving a little stem, for now, makes handling easier).
If you have multiple cultivars, you’ll want to gather some containers and label them with the cultivar names to keep the rhizomes separate.
Using a gardening fork or shovel, dig straight down about 1′ foot away from the plant, working your way around to mark the circumference.
Next, use your tool to gently pry the canna clump out of the ground and remove any excess dirt from the reboot system by hand.
#3 – Dividing And Checking The Rhizomes
You can now divide the rhizome into two or more portions, ensuring each section has at least three eyes.
Check the sections for any infestation, damage, dark spots, or foul smells.
A healthy rhizome will be a lighter brown or off-white with a whitish starchy interior, whereas signs of rot or another disease will manifest as dark brown or black flesh with a mushy texture and possible odor.
Sometimes, you can cut away small diseased spots, so there’s no discoloration left.
In the case of heavily diseased sections or those with clear signs of borers or other infestations, it’s often best to discard that section.
Finish up by printing away any remaining stalk or foliage.
#4 – Storing The Rhizome
Once you’ve checked the plant, you can dip it in a solution of 1 part bleach to 10 parts water for 30 minutes to kill any remaining bacteria.
You’ll need to let the rhizomes dry out (AKA cure) to avoid any rot in the winter.
You can do this by simply placing them in a warm, dry spot for about a week, ensuring they aren’t touching each other.
Sitting them on some newspaper in a warm garage or basement can be perfect for this step.
There are many ways to store the bulbs, but one of the most common methods is to take a cardboard box and add a layer of peat moss, coconut coir, or wood shavings.
Lay your rhizomes on this bed in a single layer, making sure they aren’t touching, then add some more of your packing material around them.
This helps keep the rhizomes dry and will allow you to inspect them for any signs of rot or infestation periodically.
Place your storage box in an excellent, dry spot where the temperature remains above freezing.
A range of 45° to 55° degrees Fahrenheit is a good, safe range, but you may go as far as 40° to 60° degrees Fahrenheit in a pinch if you keep a close eye on them to ensure they don’t sprout or rot.
#5 – Spring Health Check And Preparing The Rhizome
Once the danger of frost has passed, you can give your rhizomes another health check to ensure they weren’t damaged during the winter.
This includes looking for signs of infestation or rot and cutting away any damage as you did in the fall.
You may also give the plant another bleach solution soak and allow it to dry for 2 to 3 days, but this is rarely necessary.
Healthy rhizomes can be planted as-is or soaked for 12 to 24 hours in warm water to wake them up quicker.
You can also start them indoors in a peat pot 4 to 6 weeks before the estimated final frost to give them an extra head start, then plant the entire container.
Just remember, you’ll want to harden any plant that’s started indoors by setting it outside for a few hours, then for twice as long the next day, adding more time each week until the plant is acclimated.