Canna lilies are often mistakenly referred to as bulbs, but they actually grow from a specialized underground stem known as a rhizome. Native to tropical and subtropical regions, their heritage strongly influences their growing requirements. Their exotic, large-leaved foliage and flamboyant blooms bring a bold, architectural element to the garden. Successfully growing these tender perennials requires attention to specific conditions and a clear understanding of the planting process.
Selecting the Ideal Planting Conditions
Planting canna rhizomes must be timed precisely. The ground must be sufficiently warm, meaning the soil temperature should consistently reach at least 60°F (15°C) at a depth of two inches. This should occur after all danger of the last spring frost has passed. Planting too early in cold, wet soil is the primary cause of rhizome rot.
Cannas thrive in conditions that mimic their tropical origin, requiring full sun for at least six hours daily to produce the best flowering. While they can tolerate partial shade, a lack of sunlight results in fewer blooms and potentially weak growth. The ideal soil should be rich in organic matter, retain moisture well, and drain freely to prevent waterlogging.
If your garden has heavy clay soil, amend the area before planting to improve drainage and fertility. Digging in two to four inches of well-rotted compost, aged manure, or other organic material lightens the soil structure. This preparation ensures the rhizome has access to nutrients while preventing the stagnant moisture that causes deterioration.
Step-by-Step Canna Rhizome Planting
Once the soil is sufficiently warm, plant the canna rhizomes directly into the prepared garden bed. The growth points, often called “eyes,” should face upward. If the eyes are not clearly visible, laying the rhizome horizontally is sufficient, as the plant will orient itself toward the surface.
The planting depth is important for proper establishment and is typically shallow. Dig a hole deep enough so the rhizome is covered by one to two inches of soil. This means the bottom of the rhizome will rest about four to six inches below the surface, depending on its size. This depth allows the plant to emerge easily while providing anchorage.
Proper spacing is important, as cannas can grow quite large over a single season. Depending on the variety’s mature size, rhizomes should be spaced between one and two feet apart to allow for air circulation and root expansion. After placing the rhizome and covering it with soil, gently firm the soil to eliminate air pockets.
Ongoing Care and Winter Storage
Immediately after planting, provide a thorough, deep watering to settle the soil. Water sparingly until the first shoots break through the soil, which can take up to three weeks. Excessive moisture before growth begins can easily lead to the rhizomes rotting.
Throughout the growing season, cannas require consistent moisture, especially during hot, dry spells. Applying a balanced, slow-release fertilizer at planting time or a liquid feed every few weeks supports their rapid growth and flowering display. Deadheading spent blooms encourages the plant to produce more flowers until the season ends.
In regions colder than USDA Hardiness Zone 8, rhizomes cannot survive the winter and must be dug up for storage. After the first hard frost kills the foliage, cut the stalks down to about six inches above the soil line. Carefully lift the entire clump of rhizomes with a garden fork, ensuring they are not damaged.
Remove most of the soil from the clump and allow the rhizomes to air-dry for a few days in a protected location to cure the exterior. Once cured, store them in a cool, dark, and dry place above 40°F (4°C), such as a basement. Nesting the rhizomes in a medium like peat moss, dry sawdust, or vermiculite prevents drying out while discouraging rot.