How to Plant & Grow Hardy Canna (Thalia dealbata)

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Hardy canna Thalia dealbata in bloom
Sometimes called “powdery alligator-flag,” hardy canna is covered in a powder-like substance that repels moisture to deter fungus and rot. Photo by 阿橋 HQ, CC BY-SA 2.0

Commonly known as hardy canna, powdery Thalia, or powdery alligator-flag, Thalia dealbata is a beautiful aquatic plant with blue-green colored leaves and purple flowers. The word “powdery” is used to describe this plant because it is coated with a powdery, white, water-repelling layer that also gives it a nice dusky and muted coloration.

While people may enjoy having this showy plant in their backyard ponds simply for its ornamental value, it also provides many environmental services and benefits for wildlife. Belonging to the family Marantaceae and the genus Thalia, water canna is native in the Southern United States and Mexico. Today, it is most commonly found in the marshy lands of the southeastern region in the United States.

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Hardy Canna Fact Sheet:
Herbaceous Marginal Perennial
USDA 7 – 10
Full sun to partial shade
May – September (late Spring to Summer)
Height 91-183 cm (3-6 ft), Width ~ 61 cm (2 ft)
5-15 cm (2-6 in)
pH 6.0 – 6.5

 Facts, Benefits & Uses of Hardy Canna

An adult male lesser scaup swimming
Lesser scaup feed on the large, meaty seeds of hardy canna. Photo by Judy Gallagher, CC BY 2.0

Having hardy canna growing in your pond will not only adorn your property with its lovely colors, it will also provide the environment with many natural services. This plant is wildlife-friendly, and will also attract many beautiful butterfly and hummingbird species to your pond. Hardy canna also provides ducks with a source of food. The mallard (Anas platyrhynchos) and the lesser scaup (Aythya affinis) are among the duck species that feed on the large seeds of the hardy canna plant. The flowers of hardy canna are pollinated by carpenter bees (Xylocopa virginica) and bumblebees (Bombus spp.), who seek out the sweet nectar provided by the plant.

Phytoremediation is a natural process in which a plant is able to remove contaminants from water or soil in its environment. Hardy canna is a species that is notable for its ability to remove excess pollutants from standing water, thus providing the landscape with an invaluable environmental service. This plant also has the ability to break down these pollutants, thus improving the quality of the water in the area.

Hardy Canna Growth, Hardiness & Climate

Hardy canna Thalia dealbata flowers going to seed
Native to the warm, humid regions of the southern US, hardy canna does not tolerate cold or arid conditions. Photo by Michael Wolf, CC BY-SA 3.0

As the name suggests, hardy canna plants are quite hardy! They are fast-growing plants that require relatively little attention and care. Hardy canna roots are rhizomatic, and tend to spread quickly and proficiently. Spreading out your hardy canna plants into clumps when you plant them will help to keep spread and growth under control.

Hardy canna plants grow best in hardiness zones 7-10, but can survive below these zones with proper care and precaution. They do not grow as well in arid or freezing conditions, but if you live in suboptimal habitat and you are adamant about having hardy canna in your pond, then you can potentially make it work. Providing them with extra water in hot, dry locations and bringing them indoors for frigid winters will make it possible for them to live in imperfect environmental conditions. 

How to Plant Hardy Canna In Ponds

Thalia dealbata growing in a pond at the National Museum of Natural Science in Taiwan
Hardy canna can be planted either in moist, loamy soil or directly in water. Photo by Ping an Chang, CC BY-SA 4.0

It is best practice to germinate your hardy canna seeds indoors, because they do not have high success rates when germinated in outdoor conditions. You can purchase seeds affordably online, or find a mature plant and collect them yourself. In order to collect seeds from an adult plant, make sure that the fruit has become brown in color. To remove the seeds, give the cluster a slight shake to detach the seeds from the mature parent plant.

Before sowing your seeds, they must undergo cold stratification– the purpose of which is to prepare the seeds for germination. This is a very simple and straightforward process that can be done at home with a few tools. There are a variety of simple methods to choose from, and all are equally effective. When you are ready to plant your seeds in the springtime, use moist soil or even shallow water. Hardy canna will thrive if it is planted in rich, loamy soil containing lots of organic material.

How to Care For Hardy Canna

Thalia dealbata hardy canna blooming beside a pond
Give hardy canna ample moisture, nutrients, and sunlight, and it will be quite happy. Photo by JMK, CC BY-SA 3.0

Hardy canna plants can grow well in a wide range of soil profiles, although they grow best in rich, water-retentive soils that are well drained. While they are typically found growing partially submerged in water, making them ideal for pond margins, you can still enjoy this plant if you live in a drier climate. If your climate is on the arid side, make sure your plant receives 1-2 inches of water per week. Hardy cannas are heavy feeders, so they require plenty of compost or organic fertilizer. It is nearly impossible to give this plant an overabundance of organic nutrients.

Like many other aquatic plants, hardy canna grows best when partially submerged in water. Because this plant is perennial, the stems will become brown and shriveled – at this point, you can optimally care for your plant by cutting back these parts so that they can regrow again in the springtime.

While hardy canna is not a high maintenance species by any means, it will still require some attention every once in a while. In preparation for winter, the stems should be cut back to a few inches above the waterline.

How to Winter Hardy Canna

Hardy canna will typically do just fine through mild winters as long as the roots do not reach freezing temperatures for prolonged periods of time. Overwintering your hardy canna plant within its hardiness zone is a fairly simple and straightforward process – all you need to do is submerge your plant into deeper water.

In colder climates, however, the hardy canna requires a little bit more care and consideration. In plant hardiness zones lower than 7, hardy cannas can be dug up and stored indoors to prevent freezing. Once the first freeze of the season occurs, it is important to cut the canna’s foliage to a height of around 4-6 inches. Then, gently dig up the rhizomes and wrap them up separately in sheets of newspaper. Store them in a warm, dry area for the duration of winter. It is important that the rhizomes are stored in a crate or a box that is not covered, and in temperatures that do not drop below 4.5°C (40℉). Every few weeks, check on the stored rhizomes and dispose of any that are soft or decaying.

In hardiness zones above 7, you can leave your hardy canna plants outdoors and they will be just fine. With that being said, there are still some steps you can take to give your plants extra protection through the winter. Spreading out a layer of mulch over your plants or placing them in deeper water will provide them with some additional protection from the harsh winter conditions.

Is Hardy Canna Toxic, Poisonous or Invasive?

Hardy canna is native to the southeastern lowlands in the United States. It is found in swamps and marshy landscapes ranging from South Carolina to Florida, and westward into Missouri and Texas. If you find this plant growing outside of this range, it is technically invasive (nonnative).

Hardy canna is not known to be toxic to humans, pets, or wildlife. On the contrary, it provides a food source for many wildlife species!

Is Hardy Canna Edible? Will Fish Eat it?

While hardy canna is edible, there is no evidence that fish use it as a source of food or otherwise affect its growth. Koi, turtles, and other pond-dwelling creatures are not known to cause damage to hardy canna plants. Hardy canna does, however, provide an important habitat element for fish – the plant attracts insect and frog species that your fish can feed on.

Where to Buy Hardy Canna & Seeds? (UK & US)

If you live in the US, hardy canna can be fairly easily obtained from many local native plant nurseries as well as online. If you live outside of its native range, however, you’ll likely need to order this plant online or special order it from a nursery or aquatics shop. We strongly encourage you to seek out only plants that are native to your area to provide the greatest benefit to your pond while having the least amount of negative impact on surrounding ecosystems and wildlife.

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Rebecca H
About the author

Rebecca H

Ambitiously passionate about conservation, eco-sustainability, and having new experiences and adventures! Alongside writing, I work as a Herpetological Technician, collecting and analyzing data about endangered reptile species. I'm also skilled with the proper identification of native and invasive flora and fauna, as well as habitat assessment/restoration of a variety of ecosystem types.

Read more about Pond Informer.

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