How to Stop Canna Lilies from Spreading Out of Control in Your Garden

Canna lilies are tropical-looking flowering plants that make a stunning addition to gardens with their big lush leaves and showy blooms in vibrant colors. But their rapid growth from underground rhizomes can quickly lead to them spreading out of control if left unchecked.

Within just a few seasons, canna lilies will march across your flower beds and borders, crowding out and choking surrounding plants. Their aggressive growth and multiplication can even invade lawns and planting areas where they are not wanted.

So how do you restrain canna lilies’ vigorous spreading habit so they don’t take over your entire garden? Here are the most effective strategies and techniques for stopping and controlling the spread of canna lilies in your yard and flower beds

Why Canna Lilies Spread So Much

Canna lilies proliferate and expand so readily due to their growth habit from thick underground stems called rhizomes. The rhizomes continuously lengthen and branch out, producing new shoots and roots that colonize and occupy soil space.

Under ideal growing conditions, each canna lily plant can spread outward 1-3 feet in all directions every year. Over time, this leads to dense, impenetrable patches of canna lilies that crowd and displace other plants.

Several inherent traits enable such rampant spread:

• Rhizome Growth – The rhizomes rapidly extend and branch to invade and dominate soil.

• Underground Runners – New rhizomes shoot laterally off the main rhizome, spreading the plant’s footprint sideways.

• Dense Foliage – The broad tropical leaves heavily shade and overwhelm surrounding plants, stealing their space.

• Clump Division – Rhizome chunks that break off when disturbed readily root and establish new clumps.

Without containment measures, canna lilies will continue extending their territory each year through these inherent growth habits. But the good news is you can curb their spread with some diligent management.

Effective Ways to Stop Canna Lilies from Spreading

It takes commitment and discipline to rein in canna lilies’ tendency to rapidly expand their domain. But the following are proven methods to halt their aggressive march across your garden:

Use Physical Barriers

Physically restricting canna lily roots is the simplest approach. Either plant them in containers or install vertical root barriers around garden spaces.

• Pots and Planters – Limit spread by growing canna lilies in pots and containers that can be moved around.

• Plastic Edging – Sink 12-18″ plastic lawn edging or sheet barrier into soil to block rhizomes from traveling outward.

• Concrete Footers – Pouring a concrete curb or footer around beds creates an impenetrable underground barrier.

• Pond Liners – Burying flexible pond/pool liners around plantings blocks rhizomes from invading outside the bed.

Physical containment limits the spread of canna lily root systems. Just be sure to leave ample room for growth within the confined area. Crowding stimulates more rhizome spreading.

Aggressively Divide and Replant Annually

For canna lilies planted directly in garden beds, you must diligently dig, divide, and replant clumps each year. This prevents overcrowding and renewed spreading.

• In early spring, dig up whole plants and wash off soil to expose rhizomes.

• Break clumps into smaller individual plants or rhizome chunks with 2-5 growth eyes each.

• Replant divisions 18-24 inches apart in prepared garden soil to discourage spreading.

• Discard excess rhizome pieces, or pot extras to give away or sell.

Frequent division eliminates crowded clusters prone to spreading. It also rejuvenates growth. But it’s very labor intensive compared to barriers.

Cut Back Foliage After Frost

Removing canna leaves and stems after they die back each fall may help slow rhizome spreading. Cutting back stresses the plant, so theory suggests it curbs root growth.

Research is limited, but it’s an easy added step to try. Just be sure to mulch roots well for winter protection after cutting back spent foliage.

Grow Alternative Plants

Sometimes it’s best to simply avoid persistent spreaders like canna lilies. Instead choose better-behaved flowering plants that spread slowly or not at all, like:

• Daylilies
• Lavender
• Salvia
• Marigolds
• Zinnias

A little planning prevents rampant growth issues down the road.

When to Divide Canna Lilies to Control Spread

To restrain canna lilies, proper timing of division is key. Follow this annual schedule:

• Fall – Cut back foliage after frost. Mulch roots.

• Early Spring – Dig, divide, and replant clumps. Discard old rhizomes.

• Summer – Allow plants to grow and flower freely.

• Next Fall – Cut back and mulch for winter again. Repeat process.

Dividing just once a year prevents crowding and signals the plants to slow rhizome production. Frequent digging stresses cannas and may increase spreading.

Step-by-Step Guide to Dividing Canna Lily Clumps

Executing the division process correctly minimizes disruption to canna lilies while controlling spread. Follow these steps:

1. Cut back all foliage in fall once it browns after a hard frost. Remove stems to about 4 inches above soil. Allow the dying leaves to reabsorb nutrients back into the rhizomes.

2. In early spring, use a spade to loosen soil across the surface of the clump, then lever the entire clump up and out of the ground.

3. Wash or shake off excess soil clinging to the rhizome roots. Gently remove remaining soil with your hands to fully expose rhizomes.

4. Break the large root mass into smaller, more manageable chunks using your hands or a knife. Shoot for individual plants or clusters of 3-5 rhizomes.

5. Inspect each divided section and discard any that show signs of rot or other damage. Keep only the healthiest, most robust rhizome chunks.

6. Replant the healthiest divisions back in the prepared garden bed, spacing them 18-24 inches apart to prevent crowding and deter underground spreading.

7. Water transplants well and add mulch around each one. Stake larger pieces as needed. This reduces transplant shock and gets them growing quickly.

Execute this routine each spring to keep canna lilies under control. Preventing overcrowded clumps is key to curbing rampant spread.

Growing Canna Lilies Successfully

Even with control methods, canna lilies thrive when properly planted and cared for:

• Prepare beds with rich soil and excellent drainage. Cannas hate wet feet!

• Ensure a site with at least 6 hours of direct sun daily. More is better.

• Water 1-2 inches per week. Increase watering during periods of heat and drought.

• Stake tall varieties and mulch well around the base to retain moisture.

• Fertilize monthly with a balanced formula high in phosphorus to encourage flowering.

• Prune spent blooms to promote continuous reblooming.

• Divide crowded clumps every spring. Discard old center rhizomes.

A little TLC keeps canna lilies lush and flowering freely, yet avoids invasive spread. Pay close attention to spacing, frequent division, and care.

Do Canna Lily Rhizomes Die Over Winter?

• In zones 8-10, canna rhizomes can remain safely in the ground over winter. They go dormant once frost kills the foliage and resprout the following spring.

• But in colder zones 6-7, rhizomes dug and stored indoors over winter have higher survival rates. Prolonged cold below 10°F can kill them.

To overwinter canna rhizomes, follow these steps:

• Dig up rhizomes after first hard frost, leaving foliage intact.

• Allow clumps to dry for a few days.

• Remove dead foliage and roots, keeping only healthy rhizomes.

• Pack in slightly damp peat or vermiculite. Store above 40°F over winter.

• Next spring, divide and replant the renewed rhizomes back outside after danger of frost.

Proper storage prevents cold damage and death in harsher climates. In warmer regions, established cannas are quite resilient through winter dormancy.

Are Canna Lilies Considered Invasive Plants?

While canna lilies spread readily, they are not considered ecologically invasive plants in most regions. True invasive plants like Japanese knotweed can destroy native plant communities.

When properly contained and managed, canna lilies are unlikely to escape cultivation and cause environmental harm. Just be sure to responsibly dispose of any excess divisions.

In USDA zones 7-10, canna lilies are well-behaved landscape plants if given adequate space and care. There’s no need to avoid planting cannas, just exercise smart control methods.

Take Control of Canna Lily Spread

If left unrestrained, vigorous canna lilies will quickly march across your entire garden. That’s why it’s so important to take measures to halt their spread.

The best approach is being diligent about spring division and planting in containers or within physical barriers. A little extra effort goes a long way toward keeping canna lilies in their place.

With the right containment strategy, you can enjoy canna lilies for their tropical flair without them becoming a nuisance. Just be proactive about controlling their growth habit each season.

To prevent lilies from spreading, you can install physical barriers like edging or sub-surface barriers, plant them in containers, or use mulch and newspaper to smother them.

Yes, canna lilies multiply naturally through their rhizomes, which are underground stems. These rhizomes grow and produce new shoots, effectively creating new plants.