The Canna lily, with its dramatic foliage and vividly colored flowers, brings a distinct tropical atmosphere to any garden space. While often referred to as “bulbs,” the plant actually grows from a modified underground stem known as a rhizome. These fleshy structures store energy and are the starting point for impressive vertical growth and vibrant blooms. Knowing the precise timing and method for planting these rhizomes is key to ensuring a long and successful growing season.
When to Plant Outdoors
The success of Canna lilies planted directly into the garden depends on favorable environmental conditions. The absolute rule for outdoor planting is to wait until all danger of frost has passed, as the rhizomes are highly sensitive to cold temperatures. Even a light frost can damage tender new growth and set back the plant’s development.
Beyond the last frost date, soil temperature is the most important factor. Canna rhizomes require warm soil to break dormancy and sprout successfully. The ideal soil temperature should be consistently 60°F (16°C) or warmer, though some gardeners wait until the soil reaches 65°F for maximum growth potential. A soil thermometer inserted a few inches into the planting area provides the most accurate reading.
In regions with shorter growing seasons, this warm soil requirement means planting often occurs in late spring or early summer. In warmer, frost-free climates (USDA Zones 8 and above), rhizomes can be planted almost any time the soil is workable, though spring is preferred. Waiting for the minimum temperature ensures the rhizome does not rot in cold, damp ground before it activates.
Starting Canna Indoors
Gardeners in colder northern climates often pre-sprout Canna rhizomes indoors to gain a significant head start on the short growing season. This technique provides an extra four to eight weeks of growth time, allowing plants to bloom earlier and more profusely outdoors. The process should begin approximately four to six weeks before the last expected frost date.
Plant the rhizomes in individual containers using a quality, well-draining potting mix. Cover the rhizome with about two to three inches of the potting medium. Place the containers in a warm location, such as on a heat mat or in a sunny window, to encourage dormant growth points to activate.
Canna rhizomes do not require strong light immediately, but warmth is necessary to initiate sprouting. Once green shoots emerge, the developing plants need to be moved to a location that receives bright, direct sunlight for several hours each day. This indoor growth period allows a more mature, robust plant to be transplanted outside once warmer weather and soil temperatures have stabilized.
How to Plant Canna Rhizomes
Preparing the planting site correctly maximizes the chances of a vigorous and healthy Canna plant. Before placing the rhizomes, the soil should be loosened to a depth of at least 12 to 15 inches to accommodate the spreading root system. Canna lilies thrive in rich, fertile ground, so amending the soil with a generous amount of well-rotted compost or aged manure is beneficial.
The orientation of the rhizome during planting is important for efficient sprouting. The rhizome should be laid horizontally in the prepared hole with the small, bumpy “eyes” (the growth points) facing upward. Cover the rhizome with a thin layer of soil, aiming for a planting depth where the top is covered by about two to four inches of earth.
Proper spacing is necessary to allow the large-leafed plants to reach their full potential without overcrowding. Depending on the mature size of the variety, Canna rhizomes should be spaced between one and two feet apart. Taller cultivars require wider spacing to ensure adequate air circulation and sunlight penetration.
Initial Care After Planting
Immediately following planting, a thorough initial watering is needed to settle the soil around the rhizome. This first soaking helps eliminate air pockets that may hinder root development. However, the soil should be allowed to dry slightly before the next watering, as the rhizome can rot if kept too wet before new shoots appear.
Canna lilies are tropical plants that perform best when they receive a minimum of six to eight hours of direct sunlight each day. Positioning them in full sun promotes the most abundant flowering and deepest foliage color. Once the first shoots emerge, a consistent watering regimen must be established to keep the ground evenly moist, reflecting the plant’s high water demands.
To fuel their rapid growth and colorful displays, Canna lilies benefit from an initial feeding. Incorporating a balanced, slow-release fertilizer into the planting hole or raking it into the surrounding soil provides nutrients as the plant establishes itself. Alternatively, once shoots are actively growing, a monthly application of a high-nitrogen liquid fertilizer supports the lush development of both foliage and blooms.