Do Canna Lilies Spread? Are Canna Lilies Invasive?

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Canna lilies are excellent perennials to add to almost any garden with beautiful blooms. Cannas, being tropical plants, are a popular choice in gardening due to their vibrant and colorful foliage varieties, which add a burst of color to any landscape.  

Unfortunately, one thing rarely mentioned is the possibility of these plants getting out of control when left on their own.

Blooming Canna LiliesPin

Canna species are native to semi-tropical and tropical parts of North Australia and South America. Their native range extends from South Carolina (Canna flaccida) south to Argentina and includes the Caribbean islands.

Canna x generalis ‘Nuance’ An alternative to scarifying the seed is the hot water method. Place the seeds in a cup and pour very hot (nearly boiling) water over them.  

Much of the early breeding work with canna occurred in France. The first prominent breeder was M. Théodore Année, a French diplomat who collected Canna glauca and Canna indica in Chile and based his garden hybrids on crosses of these two species. 

They’re known to die back in winter, but what’s happening under the surface?

More importantly, why does it sometimes seem like you have more cannas than you remember planting the previous year?

Do Canna Lilies Spread?

Cannas do indeed spread, most often through their rhizomes below the surface.

Proper maintenance keeps the plants from overcrowding or escaping your garden.

Rhizomes vs. Bulbs

It’s important to distinguish between rhizomes and bulbs.

Rhizomes are swollen horizontal roots that spread underground, accompanied by smaller roots.

These particular roots store food and water and usually have a white interior.

When you cut into a rhizome, it will look like the inside of a potato.

Ginger is an excellent example of a common rhizome.

Meanwhile, bulbs grow vertically and can form offsets (which is why they’re often confused with rhizomes). The flower petals are bicolored with a central florescent red-orange color surrounded by golden-yellow.  

Bulbs will have a layered appearance, like onions, when you cut into them.

Bulbs are often uprooted and stored indoors. Rhizomes of plants need similar storage.

Despite popular belief, canna lilies have rhizomes, not bulbs.

These rhizomes often overwinter indoors, so it is typical for the gardening community to mistake them for bulbous plants.

How Do Canna Lilies Spread?

During the growing season, the rhizome of a healthy canna will spread horizontally in all directions to take advantage of the nutrients around it.

The new rhizome portions may sprout their cannas in the following year.

Eventually, the cannas within the clump begin to compete for space if not tended to.

The oldest part of the clump is in the middle. This portion will begin failing to bloom after a few years while the surrounding stalks continue to bloom.

If not divided, the younger stalks will also begin to suffer the effects of overcrowding in time.

Another cause of spreading cannas is their ability to self-seed.

Canna lily seedlings have a thick coating to protect them from damage.

This allows them to hibernate, sometimes for years, until conditions enable the seed to germinate.

When cannas are allowed to go to seed, any seeds that fall onto the ground will remain and could sprout several years later.

If you’re in the practice of uprooting and overwintering your canna rhizomes indoors, there are good chance seeds are getting mixed into the soil or even ending up in your compost pile.

How To Divide Canna Rhizomes?

While it’s not always easy to stop a canna lily from self-seeding, you can help limit the spread of your plants (and improve their health) by manually dividing them.

 When lifting canna bulbs (rhizomes), avoid damaging them, especially those cultivars with long narrow rhizomes.

This is especially important if you live in a zone where they’re left to overwinter outdoors.

Step 1: Cutting Back

In USDA hardiness zone 8, cannas will die back after the first good frost hits, at which point you can remove the dead canna foliage.

Don’t cut back cannas beforehand, as the plants are still storing up resources for the winter.

However, USDA zones 9 to 12 won’t have the same frost conditions, so keep an eye out for when the plant has stopped growing.

Cut the plant back to only a few inches above soil level.

This action will help prevent the canna from getting too cold while making it easier to work with.

Step 2: Cover The Plant

Since you aren’t overwintering indoors, leaving the roots undisturbed for now is essential.

Spread a 4″ inch (10 cm) layer of mulch over the plant to insulate it. Mulches also play a crucial role in preserving soil moisture and regulating soil temperatures consistently. 

For annual plants, utilizing an organic mulch made of shredded leaves not only adds a natural aesthetic to the garden bed but also enhances the soil quality as it gradually decomposes over time.

You may need to use more—up to 12″ inches—in zones cooler than 10a.

Step 3: Excavate

Once the danger of frost has passed the following spring, it’s time to excavate your rhizomes.

Grab a shovel, pierce the ground 4″ to 6″ inches away from the canna stems, and cut downwards, working your way around the clump.

Once you’re back at the starting point, use the shovel to pry the clump out of the ground.

Knock or shake the excess dirt off and use a hose to rinse the rhizomes further.

Step 4: Divide

When dividing canna lilies, first dig up the entire plant. Next, use a spade, sterile knife, or hands to split the rhizome into smaller clumps. 

It’s best to have two to three shoots in each clump for better growth and long-term survival.

If it’s been 2 to 3 years since you last divided, you may also wish to discard the central part of the rhizome.

Do the following steps for this procedure:

  • Now divide the rhizome chunks into smaller sections with at least three eyes each.
  • Discard any sections that appear to be rotting, diseased, or damaged.
  • Soak the healthy rhizomes in a solution of 1 part bleach to 9 parts water for up to 30 minutes.
  • Rinse them, then pat dry with a soft cloth or paper towel.

To protect canna rhizomes from fungi and bacteria, dust them with sulfur. Ensure the rhizomes are kept cool, below 50° degrees Fahrenheit, but avoid freezing them. 

An ideal storage location would be a garage, crawl space, or basement. Be cautious not to let the peat dry out excessively during the winter to maintain their health.

It’s usually best to allow them to air dry for 2 to 3 days before replanting.

Step 5: Replant

Finally, it’s time to replant the plant canna rhizomes.

Space them about 30″ inches apart and plant to a depth of 4″ inches.

You can also plant individual rhizomes in 12″ inch pots.

Any leftover rhizomes may be discarded or given away.

Threats to Cannas

Once you’ve successfully multiplied your canna plants, it’s crucial to be aware of potential threats that could harm their well-being. 

Understanding these risks will help you protect your canna garden effectively.

1. Plant Viruses

The first one on the list is viruses. Canna plants are susceptible to various viruses that can cause infections, such as bean yellow mosaic virus, hippeastrum mosaic virus, tomato aspermy virus, cucumber mosaic virus, canna yellow streak virus, and the particularly severe canna yellow mottle virus. 

Controlling aphids will help limit the spread of the virus. If you are having problems with viruses, do not propagate from these plants. 

No cure exists for virus infections in canna plants, except for doing preventive measures or removing and destroying the infected plant.  

2. Lighting and Fertilizers

Have you ever witnessed your cannas in bloom? If not, this could be attributed to inadequate sunlight or excessive fertilizer usage.

For optimal blooming, canna plants require full sun exposure, but in the extremely southern parts of the US, the strong sunlight might fade canna lily yellow flowers. 

Canna flowers range in color from pale yellow to orange to blood-red and all shades in between (salmon, apricot, and pink).  

Offering partial shade can be beneficial, particularly in the arid Southwest, where reduced humidity and soil moisture can lead to leaf scorching. 

Fertilization with cannas is done with a slow-release fertilizer specifically formulated for flowering plants or organic fertilizer like compost. 

While canna lilies may not be overly demanding, they can be considered heavy feeders like bananas during their active growth and blooming periods. 

They thrive best in nutrient-rich soil during these stages, which contributes to their optimal growth and vibrant blooms.

Besides these two things, pruning can also increase the bloom.  By ensuring these conditions are met, you can encourage your cannas to showcase their vibrant blooms in all their glory.

3. Pests

Cannas are no strangers to the appetites of minor pests like slugs, snails, caterpillars (canna leaf roller), and Japanese beetles. 

These pesky invaders can wreak havoc on the plants by munching on their wonderful green leaves and indulging in their delightful orange flowers. 

However, by adopting sound organic soil preparation practices and refraining from chemical fertilizers, you can effectively reduce the incidence of slug and snail issues. 

Embracing these eco-friendly methods helps preserve the natural predators of these pests, ensuring a healthier balance in the garden and keeping these marauders at bay.

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