Canna lilies are large plants that add bold, tropical texture to a garden, whether used in containers or planted directly in the ground. In cool climates, cannas are fast-growing plants that are treated as annuals to fill a space with color quickly. In warm climates, they create dense stands of lush foliage and vibrant blooms throughout the summer, year after year. This guide covers how to plant and grow canna lilies in garden beds and containers.
I. Appearance and Characteristics
Canna or canna lily is the only genus of flowering plants in the family Cannaceae, consisting of 10 species. All of the genus’s species are native to the American tropics and naturalized in Europe, India and Africa in the 1860s.
The plants are large tropical and subtropical herbaceous perennials with a rhizomatous rootstock. The broad, flat, alternate leaves that are such a feature of these plants, grow out of a stem in a long, narrow roll and then unfurl. The leaves are typically solid green, but some cultivars have glaucose, brownish, maroon, or even variegated leaves.
The flowers are asymmetric and composed of three sepals and three petals that are small, inconspicuous, and hidden under extravagant stamens. What appear to be petals are the highly modified stamens or staminodes. The staminodes number (1–) 3 (–4) (with at least one staminodal member called the labellum, always being present. A specialized staminode, the stamen, bears pollen from a half-anther. A somewhat narrower “petal” is the pistil, which is connected down to a three-chambered ovary.
The flowers are typically red, orange, or yellow, or any combination of those colours, and are aggregated in inflorescences that are spikes or panicles (thyrses). The main pollinators of the flowers are bees, hummingbirds, sunbirds, and bats. The pollination mechanism is conspicuously specialized. Pollen is shed on the style while still in the bud, and in the species and early hybrids, some is also found on the stigma because of the high position of the anther, which means that they are self-pollinating. Later cultivars have a lower anther, and rely on pollinators alighting on the labellum and touching first the terminal stigma, and then the pollen.
The wild species often grow to at least 2–3 m (6.6–9.8 ft) in height, but wide variation in size exists among cultivated plants; numerous cultivars have been selected for smaller stature.
Cannas grow from swollen underground stems, correctly known as rhizomes, which store starch, and this is the main attraction of the plant to agriculture, having the largest starch grains of all plant life.
Canna is the only member of the Liliopsida class (monocot group) in which hibernation of seed is known to occur, due to its hard, impenetrable seed covering.
Cannas grow best in full sun with moderate water in well-drained, rich or sandy soil. They grow from perennial rhizomes, but are frequently grown as annuals in temperate zones for an exotic or tropical look in the garden. In arid regions, cannas are often grown in the water garden, with the lower inch of pot submerged. In all areas, high winds tear the leaves, so shelter is advised.
The rhizomes are sensitive to frost and will rot if left unprotected in freezing conditions. In areas with winter temperatures below −10 °C (14 °F) in the winter (< USDA Zone 8b), the rhizomes can be dug up before freezing and stored (above 7 °C or 45 °F) for replanting in the spring. Otherwise, they should be protected by a thick layer of mulch over winter.
II. How to Grow and Care
Sunlight
As a group, cannas tolerate a variety of sun conditions. Older varieties and species tolerate some shade, but full sun brings out the best leaf color and flower show. Cannas growing in warm southern climates need a bit of afternoon shade to keep foliage from bleaching. Taller varieties need full sun to prevent flopping, which necessitates staking.
Temperature and Humidity
Cannas prefer humid air and are evergreen in the warmest areas. They won’t survive a frost, although their rhizomes may. They like sun and are comfortable with temperatures as warm as 90°F or slightly higher. In cooler areas, they can be dug up and overwintered.
Soil and Water
In their native habitats, cannas are often seen growing close to and even in the water. These plants also do fine in regular garden soil as long as they get consistent moisture, especially in warmer climates. When planted in the ground, they need plenty of compost and other organic matter.
Fertilizing
Cannas are heavy feeders. Apply a slow-release granular fertilizer (5-10-5 or 10-10-10) to the soil to keep cannas relatively happy. An occasional dose of liquid flower fertilizer (following the label directions) keeps them looking their best during the bloom season.
Pruning
During the growing season, trim off any dead or damaged leaves at the bottom and deadhead the blooms regularly to prolong flowering. In fall, wait until the first hard frost kills off the foliage and cut it off at ground level.
Propagation
Sexual propagation
Seeds are produced from sexual reproduction, involving the transfer of pollen from the stamen of the pollen parent onto the stigma of the seed parent. In the case of Canna, the same plant can usually play the roles of both pollen and seed parents, technically referred to as a hermaphrodite. However, the cultivars of the Italian group and triploids are almost always seed sterile, and their pollen has a low fertility level. Mutations are almost always totally sterile.
Canna seeds have a very hard seed coat, which contributes to their dormancy. Germination is facilitated by scarification of the seed coat, which can be accomplished by several techniques.
- Pollination
The species are capable of self-pollination, but most cultivars require an outside pollinator. All cannas produce nectar, so attract nectar-consuming insects, bats, and hummingbirds that act as the transfer agent, spreading pollen between stamens and stigmas on the same or different flowers.
- Genetic changes
Since genetic recombination has occurred, a cultivar grown from seed will have different characteristics from its parent(s), thus should never be given a parent’s name. The wild species have evolved in the absence of other Canna genes and are usually true to type when the parents are of the same species, but a degree of variance still occurs. The species C. indica is an aggregate species, having many different and extreme forms ranging from the giant to miniature, from large foliage to small foliage, both green and dark foliage, and many differently coloured blooms of red, orange, pink, or yellow, and combinations of those colors.
Asexual propagation
- Division of plant parts
Outside of a laboratory, the only effective asexual propagation method is rhizome division. This uses material from a single parent, and as no exchange of genetic material occurs, it almost always produces plants that are identical to the parent. After a summer’s growth, the horticultural cultivars can be separated into typically four or five separate smaller rhizomes, each with a growing nodal point (growing eye). Without the growing point, which is composed of meristem material, the rhizome will not grow.
- Micropropagation
Micropropagation, also known as tissue culture, is the practice of rapidly multiplying stock plant material to produce a large number of progeny plants. Micropropagation uses in vitro division of small pieces in a sterile environment, where they first produce proliferations of tissue, which are then separated into small pieces that are treated differently so that they produce roots and new stem tissue. The steps in the process are regulated by different ratios of plant growth regulators. Many commercial organizations have produced cannas this way, and specifically the “Island Series” of cannas was introduced by means of mass-produced plants using this technique. However, cannas have a reputation for being difficult micropropagation candidates.
Micropropagation techniques can be employed to disinfect plants of a virus. In the growing tip of a plant, cell division is so rapid that the younger cells may not have had time to be infected with the virus. The rapidly growing region of meristem cells producing the shoot tip is cut off and placed in vitro, with a very high probability of being uncontaminated by virus.
Potting and Repotting
Bigger is better when potting a canna in a container. The roots need a lot of space to grow, and the plant will soon be tall. Select a ceramic, terra-cotta or plastic container—or half a whiskey barrel—making sure it has drainage holes. Fill the container to within a couple of inches of the top with good-quality garden soil amended with compost. Plant the rhizomes about 5 inches deep with the “eye” pointing upward.
Canna roots spread rapidly and become crowded, so the plant will need to be divided and repotted every year or two.
Overwintering
As the first frost approaches, gardeners in cool zones need to think about overwintering their cannas. If the cannas are being grown in containers, keep them in the same pot and withhold water as temperatures drop in late fall. Once the foliage begins to die back, move the pots to a cool, dark place, such as an unheated garage or basement. Keep the soil dry throughout the winter until spring warms back up and watering can resume.
If the cannas grow directly in the ground, dig the tender rhizomes after the first frost knocks back the foliage. Store them in a dry, cool, dark place after wrapping them in dry to slightly moist peat moss (no two rhizomes should touch), and then place them in a plastic bag with a few holes cut for aeration. Once the soil has thawed and all danger of frost has passed (probably late spring), unwrap the rhizomes and plant them directly in the ground.
Pests and Diseases
- Common Pests
Cannas are largely free of pests, but in the US, plants sometimes fall victim to the canna leaf roller moth, and the resultant leaf damage, while not fatal to the plant, can be most distressing to a keen gardener.
Slugs and snails are fond of cannas’ large and juicy leaves, potentially leaving large and unsightly holes where they have eaten. The mollusks prefer the tender, young, unfurled leaves. Red spider mites and mealybug can also be a problem for cannas grown indoors, or outside during very hot, long summers, particularly in drier climates. Japanese beetles can also ravage the leaves if left uncontrolled.
- Common Disease
Cannas are remarkably free of diseases, compared to many genera. However, they may fall victim to canna rust, a fungal disease resulting in orange spots on the plant’s leaves, caused by over-moist soil. They are also susceptible to certain plant viruses, some of which are Canna-specific, which may result in spotted or streaked leaves, in a mild form, but can finally result in stunted growth and twisted and distorted blooms and foliage.
The flowers are sometimes affected by a grey, fuzzy mold called botrytis. Under humid conditions, it is often found growing on the older flowers. Treatment is to simply remove the old flowers, so the mold does not spread to the new flowers.
III. Uses and Benefits
- Some species and many cultivars are widely grown in the garden in temperate and subtropical regions. Sometimes, they are also grown as potted plants. A large number of ornamental cultivars have been developed. They can be used in herbaceous borders, tropical plantings, and as a patio or decking plant.
- Internationally, cannas are one of the most popular garden plants, and a large horticultural industry depends on the plant.
- The rhizomes of cannas are rich in starch, and have many uses in agriculture. All of the plant material has commercial value, rhizomes for starch (consumption by humans and livestock), stems and foliage for animal fodder, young shoots as a vegetable, and young seeds as an addition to tortillas.
- The seeds are used as beads in jewelry.
- The seeds are used as the mobile elements of the kayamb, a musical instrument from Réunion, as well as the hosho, a gourd rattle from Zimbabwe, where the seeds are known as hota seeds.
- In more remote regions of India, cannas are fermented to produce alcohol.
- The plant yields a fibre from the stem, which is used as a jute substitute.
- A fibre obtained from the leaves is used for making paper. The leaves are harvested in late summer after the plant has flowered, they are scraped to remove the outer skin, and are then soaked in water for two hours prior to cooking. The fibres are cooked for 24 hours with lye and then beaten in a blender. They make a light tan to brown paper.
- A purple dye is obtained from the seed.
- Smoke from the burning leaves is said to be insecticidal.
- Cannas are used to extract many undesirable pollutants in a wetland environment as they have a high tolerance to contaminants.
- In Thailand, cannas are a traditional gift for Father’s Day.
- In Vietnam, canna starch is used to make cellophane noodles known as miến dong.
- Cannas attract hummingbirds, so can be part of a pollinator and wildlife habitat strategy.
