Table of Contents
- Introduction
- The Natural History of Water-Loving Cannas
- Identifying the Best Cannas for Water
- The Secret to Transitioning Cannas to Water
- How to Pot Cannas for Aquatic Growth
- Placing Your Cannas in the Water Feature
- Nutrient Management in a Water Environment
- Water Quality and Plant Health
- Maintaining Your Aquatic Cannas
- Overwintering Cannas Grown in Water
- Designing a Water Feature with Cannas
- Common Questions for Success
- Conclusion
- FAQ
Introduction
There is nothing quite like the lush, architectural beauty of canna lilies to transform a standard backyard into a tropical oasis. Their oversized leaves and vibrant, orchid-like blooms bring a sense of drama and height that few other plants can match. If you have a pond, a water feature, or even a soggy corner of the yard where other plants struggle, you might find yourself wondering if these sun-loving giants can thrive with their roots submerged.
At Longfield Gardens, we love helping gardeners experiment with versatile plants that have high impact for minimal effort. Cannas are famous for their ability to thrive in traditional garden beds, but their history and biology actually make them excellent candidates for water gardening. This guide is designed for home gardeners who want to explore the aquatic potential of cannas and learn the simple steps to keep them healthy in a watery environment.
By understanding a few basic needs regarding depth, soil, and timing, you can enjoy these spectacular plants in your pond or water garden all summer long. While they are often sold as traditional perennials, many cannas are perfectly happy with "wet feet."
The Natural History of Water-Loving Cannas
To understand why cannas grow so well in water, it helps to look at where they come from. Most modern canna hybrids have roots that trace back to the wetlands of Central and South America. In their native habitats, these plants are often found growing along the edges of rivers, marshes, and ponds. They are biologically adapted to handle saturated soil conditions that would cause many other bulbs and rhizomes to rot.
This semi-aquatic heritage means that cannas have developed a specialized root system capable of absorbing nutrients and oxygen even when submerged. While we often think of them as desert-dwellers because they love the heat, they are actually moisture-seekers at heart. This unique flexibility allows them to bridge the gap between a standard flower border and a formal water feature.
Most varieties will perform beautifully in a "bog" setting, which is soil that remains constantly saturated but isn't necessarily under deep water. However, certain types, often referred to as "water cannas," have been specifically selected for their ability to thrive with their crowns completely submerged. Whether you are planting a classic variety like Tropicanna or a specialized aquatic hybrid, the key to success lies in mimicking these natural wetland conditions.
Identifying the Best Cannas for Water
While almost any canna will tolerate wet soil for a period of time, some are better suited for permanent placement in a pond than others. When selecting varieties for your water feature, look for those known for their vigorous growth and sturdy stems.
- Canna glauca hybrids: These are the true "water cannas." They have been bred specifically for aquatic environments and often feature narrower, more blue-green foliage than their land-based cousins. They are exceptionally resistant to rot and can handle deeper water levels.
- Large-leafed varieties: Popular choices such as Tropicanna, The President, and City of Portland are remarkably adaptable. Their bold, variegated foliage looks stunning reflecting off the surface of a pond, and they generally transition well to aquatic life if they are started correctly.
- Standard garden hybrids: Many of the classic red, yellow, and orange cannas found in our collection, such as the Canna Assorted Collection, can also grow in water. They simply require a slightly shallower placement and a bit more attention during the initial transition period.
The primary difference between a "water canna" and a "land canna" is often just the plant's history of cultivation. In a home garden setting, the most important factor is the health of the rhizome and how you introduce it to the water. A healthy, firm rhizome with several growing points (called "eyes") will have the energy required to adapt to a new environment.
The Secret to Transitioning Cannas to Water
One of the most common mistakes gardeners make is taking a dry, dormant rhizome and tossing it directly into a deep pond. While cannas love water, the rhizome needs to be actively growing before it can handle being submerged. If a dormant rhizome is placed in cold, deep water, it may struggle to wake up and could eventually succumb to rot before it ever sends up a leaf.
The most successful method is to start your cannas in pots on dry land first. By giving them a head start in a warm, controlled environment, you ensure the plant has a functioning root system and at least one or two emerged leaves before it enters the water. This "waking up" period typically takes four to six weeks.
Once the plant is about 6 to 10 inches tall and the weather has warmed up, you can begin moving it toward the water. This gradual approach allows the plant to adjust its cellular structure to the aquatic environment. It is much easier for an established plant to transition to "wet feet" than it is for a dormant one to start from scratch under several inches of water.
Key Takeaway: Always start your canna rhizomes in pots with soil first. Wait until the plant is actively growing with visible green leaves before submerging the pot into your pond or water feature.
How to Pot Cannas for Aquatic Growth
Potting a canna for a pond is a bit different than potting one for your patio. In a standard container, you want light, airy soil that drains quickly. In a pond, you want the exact opposite. If you use a standard potting mix containing perlite or vermiculite, those white bits will float right out of the pot and create a messy film on your pond’s surface.
Choosing the Right Soil
For water gardening, heavy garden soil or a specialized aquatic planting medium is best. A soil with a high clay content is ideal because it stays put and holds onto nutrients. Avoid any mixes with added "wood products" or organic fertilizers that can break down underwater and deplete oxygen levels, which can be harmful to fish.
Selecting the Container
Use a sturdy plastic pot that is at least 12 inches in diameter. Since cannas have powerful, spreading rhizomes, they can actually break thin plastic or ceramic pots over time. Ensure the pot has drainage holes. While this might seem counterintuitive for a plant sitting in water, the holes allow for gas exchange and let the roots grow out into the surrounding water or gravel.
Planting Depth in the Pot
Place the rhizome about 2 to 3 inches deep in the heavy soil, making sure the growing points are facing up. Press the soil down firmly around the rhizome to remove any large air pockets. To prevent the soil from washing away once the pot is submerged, many gardeners add a 1-inch layer of pea gravel or small river stones to the top of the soil. This "cap" keeps the soil in the pot and prevents curious fish from digging at the roots.
Placing Your Cannas in the Water Feature
Once your canna is potted and growing, it’s time to find the perfect spot in your water feature. Placement is about more than just looks; it’s about ensuring the plant gets enough light and is at the correct depth.
Sun Requirements
Cannas are sun-worshippers. To produce those brilliant blooms and maintain vibrant foliage color, they need at least 6 to 8 hours of direct sunlight every day. If they are placed in a shaded corner of a pond, they will likely become "leggy," stretching toward the light and failing to flower. The reflected light from the water surface can actually help boost their growth, so don't be afraid to put them in the brightest spot you have.
Submergence Depth
The "sweet spot" for most cannas is 2 to 6 inches of water over the top of the pot. This means the crown of the plant—where the stems emerge from the soil—should be just below or at the water's surface. While true aquatic varieties can handle depths of up to 12 inches, most garden varieties prefer to stay in the shallower "shelf" areas of a pond.
If your pond is deeper than 6 inches, you can easily adjust the height of the plant by setting the pot on top of inverted bricks or milk crates. This allows you to place the canna anywhere in the pond while keeping the roots at the ideal level.
Steps for Placement:
- Check that the water temperature is at least 60°F (15°C) before submerging.
- Lower the pot slowly into the water to avoid disturbing the soil cap.
- Position the pot on a sturdy, level shelf or on bricks to reach the desired depth.
- Ensure the stems are clear of any splashing water from fountains or waterfalls, as constant spray can damage the leaves.
Nutrient Management in a Water Environment
Cannas are "heavy feeders," meaning they require a lot of nutrients to fuel their rapid growth and large flowers. In a traditional garden, you would simply sprinkle some granular fertilizer around the base. In a pond, fertilizing requires a bit more strategy to avoid causing an algae bloom.
Excess nutrients in pond water can lead to "pea soup" green water or stringy algae. To feed your cannas without feeding the algae, use aquatic fertilizer tablets. These are designed to be pushed deep into the soil inside the pot, near the roots. This keeps the nutrients concentrated where the plant can use them, rather than letting them dissolve into the open water.
Depending on your climate and the length of your growing season, you may need to fertilize your water-grown cannas every 4 to 6 weeks. Watch the foliage for clues; if the leaves start to look pale or the plant stops producing new flower spikes, it’s likely time for a boost.
Water Quality and Plant Health
Growing cannas in water can actually improve the health of your pond. Like many aquatic plants, cannas act as natural filters. Their extensive root systems absorb excess nitrates and phosphates from the water—nutrients that would otherwise fuel algae growth.
If you have a fish pond, cannas provide another benefit: they help oxygenate the water and provide shade. The large leaves of a Tropicanna or City of Portland can shade a significant portion of the water surface, keeping the water cooler for fish like koi or goldfish during the peak of summer. Just be aware that koi are curious and may nibble on the tender roots if they are not protected by a gravel cap or a mesh basket.
If you notice the water becoming cloudy or develop a film after adding your cannas, don't worry. This is often just a temporary adjustment period as the soil in the pot settles and the plant begins to draw nutrients from the water. Maintaining a balance of plants, aeration, and filtration is the best way to keep a water garden crystal clear.
Maintaining Your Aquatic Cannas
One of the best things about growing cannas in water is that you never have to worry about watering them! However, they still benefit from a little bit of grooming to keep them looking their best.
Deadheading
To encourage a continuous display of flowers, remove the spent blooms regularly. Once a flower spike has finished blooming, cut the stem back to the next side shoot where a new bud is forming. If the entire stalk has finished flowering and no new buds are visible, you can cut that stalk down to the water line. This redirects the plant's energy into producing new, healthy growth from the rhizome.
Managing Foliage
Canna leaves are broad and thin, which makes them susceptible to wind damage. In a pond setting, they may occasionally look a bit "tattered" after a summer storm. Simply trim away any torn or browned leaves at the base. New leaves grow quickly from the center of the stalk, so the plant will refresh itself in no time.
Dividing
In a water garden, cannas can grow with surprising speed. Within a single season, a single rhizome can fill a 12-inch pot. If the plant starts to look crowded or if the pot begins to bulge, it’s time to divide. This is usually done in the spring before the plant goes back into the water, but it can be done in mid-summer if the plant is becoming unmanageable.
Key Takeaway: Regular deadheading and removing old foliage will keep your aquatic cannas looking lush and encourage a longer blooming season.
Overwintering Cannas Grown in Water
Cannas are tender perennials, which means they cannot survive freezing temperatures. While the water in a pond may provide a small amount of insulation, the rhizomes will eventually die if they are allowed to freeze solid. If you live in a region with cold winters, you will need to bring your cannas indoors once the weather turns.
The Lifting Process
Wait until the first light frost has blackened the foliage. This signal tells the plant to move its energy down into the rhizome for winter storage. Lift the pot out of the water and let it drain for a day or two. Cut the stems down to about 4 or 6 inches above the soil line.
Storage Methods
You have two main options for storing your water-grown cannas:
- Dormant Storage: Remove the rhizomes from the pot, wash off the soil, and let them dry in a shaded spot for a few days. Once dry, store them in a box filled with peat moss, perlite, or wood shavings. Keep the box in a cool, dark, frost-free place (like a basement or crawlspace) that stays between 40°F and 50°F.
- Indoor Growth: If you have a bright, warm sunroom or a heated greenhouse, you can keep your cannas growing all winter. Keep the pots moist but not submerged, and ensure they get plenty of light. This is a great way to have "instant" large plants ready for the pond next spring.
We provide detailed guides on overwintering all types of bulbs on our website, and the process for water-grown cannas is very similar to those grown in the ground. The most important rule is to keep them from freezing and to check them once a month during the winter to ensure they aren't drying out completely or developing rot.
Designing a Water Feature with Cannas
The vertical drama of cannas makes them the perfect "thriller" for aquatic container gardens and ponds. Because they grow tall, they are best placed toward the back or center of a water feature.
- Color Echoing: Pair the orange blooms of Tropicanna with smaller floating plants that have yellow or orange tones.
- Textural Contrast: The broad, flat leaves of cannas look spectacular when contrasted with the fine, feathery foliage of papyrus or horsetail rush.
- Living Privacy Screens: If your pond is near a seating area, a row of tall cannas can act as a lush, flowering privacy screen that softens the edges of the water feature.
Regardless of your design style, cannas bring a sense of abundance and life to the water. Their ability to grow in both soil and water makes them one of the most versatile tools in a gardener's kit.
Common Questions for Success
As you begin your aquatic canna journey, you might encounter a few questions. Here are the most likely scenarios you'll face and the simplest ways to handle them.
What if my canna stops blooming?
Lack of flowers is almost always due to a lack of sun or nutrients. If your plant looks healthy but isn't blooming, try moving the pot to a sunnier spot or adding an aquatic fertilizer tablet. Also, ensure the water isn't too deep; if the plant is struggling to reach the surface, it may put all its energy into stem growth rather than flowers.
Why are the leaf edges turning brown?
While cannas love water, brown edges can sometimes indicate a salt buildup from fertilizers or a reaction to chlorine if you've recently topped off your pond with tap water. Using a water conditioner for your pond or allowing tap water to sit for 24 hours before adding it can help. In very hot, dry climates, the edges may also brown from the intensity of the sun; providing a little afternoon shade can solve this.
Can I grow cannas in a container without a pond?
Yes! You can create a "patio pond" by using a decorative, waterproof pot without drainage holes. Simply place your potted canna inside the larger decorative pot and fill the decorative pot with water until it reaches the top of the inner pot. This is a great way to enjoy aquatic cannas on a balcony or deck.
Are cannas safe for fish?
Generally, yes. Cannas are not known to be toxic to fish. They help clean the water and provide shelter. However, as with any plant, if a large amount of foliage dies and rots in the water, it can affect the water chemistry. Always remove dead leaves and spent flowers promptly to keep the water healthy for your aquatic life.
Conclusion
Growing cannas in water is a rewarding way to expand your gardening horizons and bring a true tropical feel to your home landscape. By leveraging their natural wetland ancestry, you can turn a simple pond into a vibrant, flowering centerpiece. Whether you are using them to filter your water, shade your fish, or simply provide a stunning backdrop for summer parties, these plants are sure to impress.
At Longfield Gardens, we believe that gardening should be a source of joy and creative expression. Cannas are the perfect example of a plant that is both easy to grow and incredibly versatile. As long as you provide them with plenty of sunshine, a bit of warmth, and a steady supply of nutrients, they will reward you with spectacular foliage and blooms all season long.
Key Takeaway: Success with cannas in water comes down to three things: starting with an active plant, choosing the right "heavy" soil, and ensuring they have plenty of direct sunlight.
Ready to add a splash of color to your water feature? Start by selecting a few of your favorite varieties and giving them a head start in pots this spring. Before you know it, you’ll have a thriving aquatic garden that brings the beauty of the tropics right to your back door.
FAQ
Can any variety of canna lily grow in water?
Most canna varieties are very adaptable and can grow in water if they are transitioned properly. While true "water cannas" (like Canna glauca hybrids) are the most resilient, popular garden types like Tropicanna and The President also thrive in aquatic settings. The key is to ensure the plant is actively growing before you submerge it in the pond.
How deep should I submerge my canna lily pot?
The ideal depth for most canna lilies is 2 to 6 inches of water over the top of the pot. This keeps the rhizome and the crown of the plant submerged or right at the water line. If your pond is deeper, you can use bricks or an overturned pot to raise the plant to the correct level.
Do cannas in water need special fertilizer?
Yes, you should use aquatic fertilizer tablets rather than standard garden fertilizer. These tablets are designed to be pushed into the soil in the pot, allowing the roots to absorb nutrients without releasing them into the pond water. This prevents the fertilizer from causing algae blooms or harming fish.
Will my canna lily rhizomes rot if they stay in water all summer?
Canna rhizomes are naturally adapted to wet conditions and will not rot during the growing season as long as the water is warm and the plant is getting plenty of sun. However, they should not be left in cold, stagnant water during the winter. Once the weather turns cold, the rhizomes should be lifted and stored in a dry, frost-free location.