Canna lilies are vibrant, tropical plants celebrated for their showy foliage and striking flowers. While often mistaken for true bulbs, these plants possess a unique underground structure: the rhizome. Understanding this root system is fundamental to their successful cultivation, enabling proper planting, robust growth, and effective propagation.
Anatomy and Function of the Canna Root System
The canna lily’s underground system consists of rhizomes and fibrous roots. Rhizomes are modified underground stems that grow horizontally, distinguishing them from true roots. These fleshy, tuberous structures store water and nutrients for perennial growth. They feature “eyes” or growth points, which are dormant buds capable of sprouting new shoots and roots.
Emerging from these rhizomes are numerous thinner, thread-like fibrous roots. These roots spread into the soil, absorbing water and dissolved minerals. Fibrous roots also provide anchorage, securing the tall canna plant. Both rhizomes and fibrous roots work in concert, with rhizomes providing stored resources and fibrous roots supplying current needs, supporting the canna lily’s health and stature.
Planting and Growth Considerations
Successful canna lily establishment requires suitable soil conditions. Cannas thrive in well-draining soil rich in organic matter, which facilitates healthy rhizome development and nutrient absorption. A soil pH between 6.0 and 6.5 is optimal, allowing for proper nutrient availability and preventing rot.
When planting rhizomes, proper depth and spacing are important. Rhizomes should be planted shallowly, 1 to 2 inches below the soil surface, with any visible “eyes” pointed upwards. Spacing them 18 to 24 inches apart provides ample room for rhizomes to spread and multiply without overcrowding. Consistent moisture is beneficial, requiring regular watering, especially during dry periods, but avoiding waterlogged conditions that can damage rhizomes.
Fibrous roots absorb nutrients from the soil, which are then transported and stored within the rhizomes. Incorporating a balanced slow-release fertilizer at planting and supplementing with liquid feeds every 4 to 6 weeks during the active growing season supports growth and flowering.
Propagating Canna Lilies Through Roots
Propagating canna lilies is achieved by dividing their rhizomes. The ideal time for division is early spring before new growth emerges, or in the fall after foliage dies back. Dividing overgrown clumps every 3 to 5 years rejuvenates plants and prevents overcrowding.
To divide, carefully dig up the entire rhizome clump. Gently remove excess soil to expose the rhizomes and identify individual sections, each needing at least one “eye” or growth point. Using a clean, sharp knife or spade, cut the rhizome into smaller divisions, ensuring each piece has some fibrous roots attached.
After division, allowing the cut surfaces to “cure” or dry for a day or two helps prevent rot when replanting. These newly divided rhizome sections can then be planted directly into prepared soil at the appropriate depth and spacing.
Overwintering Canna Lilies
Canna lilies are not cold-hardy in many regions; their rhizomes require protection from freezing temperatures. In USDA hardiness zones 7 to 10, cannas may remain in the ground year-round, often benefiting from a layer of mulch. In zones 6 and colder, lift rhizomes before the ground freezes.
The overwintering process begins after the first light frost causes foliage to die back. Cut stems back to about 2 to 6 inches above the rhizome. Carefully dig up the rhizome clumps, shaking off excess soil.
After digging, allow rhizomes to air dry in a well-ventilated area for several days to prevent rot during storage. Store cured rhizomes in a cool, dark, and dry place where temperatures remain between 40°F and 50°F, such as a basement or garage. They can be stored in:
Cardboard boxes
Paper bags
Peat moss
Sand
Vermiculite
Ensure good air circulation and prevent contact between individual rhizomes.
Common Root System Problems
Canna lily root systems can encounter several issues. Rhizome rot is a common problem, often caused by overwatering, poor soil drainage, or improper storage. Symptoms include mushy, discolored, or foul-smelling rhizomes; a cottony fungal growth may also be present. Improving drainage, adjusting watering, and ensuring proper air circulation during storage can help prevent this.
Pests can affect canna lily roots, though root-specific pests are less common than foliage pests. Poor root health can make plants more susceptible to stressors. If rhizomes develop poorly, it can indicate insufficient light, inadequate nutrients, or overcrowding. Addressing these factors by ensuring full sun exposure, regular fertilization, and dividing congested clumps promotes plant vitality.