Canna lilies are dramatic, fast-growing tropical plants cultivated for their bold foliage and vibrant, iris-like flowers. Although often referred to as bulbs, cannas grow from thick, underground stems called rhizomes. These rhizomes store energy and spread horizontally beneath the soil, producing new shoots each season. Understanding this growth habit is the first step in determining planting density, as proper spacing governs both the health and the visual impact of your display.
Standard Spacing for Garden Beds
The typical distance between canna rhizomes planted in open ground is determined by the mature size of the chosen cultivar. Standard varieties, which reach three to five feet, require 18 to 24 inches between planting sites. This spacing allows the rhizomes adequate room to multiply and expand throughout the growing season.
Sufficient space also prevents disease by ensuring proper air circulation around the dense foliage. When plants are packed too closely, the resulting humidity and lack of airflow can promote fungal issues, such as rust or leaf spot. For particularly large cultivars exceeding six feet, increasing the distance to 30 or 36 inches is advisable. Dwarf canna varieties, which top out under two feet, can be planted slightly closer, often within a 12 to 18-inch range, to create a fuller grouping.
Adjusting Density for Aesthetic Goals
While standard spacing promotes healthy individual plant growth, gardeners often modify density to achieve specific visual effects. To create a dense, continuous wall of foliage, such as a privacy screen or backdrop, spacing can be reduced. Planting rhizomes 12 to 18 inches apart forces shoots to grow more vertically and quickly fill in the gaps.
This closer mass planting yields an immediate, lush appearance but requires greater maintenance. Reduced separation means the plants compete intensely for soil nutrients and moisture, necessitating a more aggressive watering and feeding schedule. Conversely, if the canna is intended as a distinct focal point, wider spacing is appropriate. Allowing 3 feet of separation or more enables the plant to develop into a massive, well-defined clump, showcasing its robust structure.
Grouping Cannas in Containers
Container planting introduces different spacing constraints, as the limited volume of soil dictates how many rhizomes can be supported. Cannas are commonly grown in pots and are often intentionally crowded to achieve an immediate, fuller display than is practical in the ground. For a standard 12-inch diameter container, a single large rhizome is typically sufficient to fill the pot by mid-season.
For larger containers (16 to 20 inches in diameter), two to three rhizomes can be planted, spaced evenly around the perimeter. In an oversized planter, such as a half-barrel, up to five rhizomes can be grouped, provided they are placed at least 6 to 8 inches apart. The trade-off for this intentional crowding is that plants rapidly deplete resources, demanding more frequent watering and regular liquid feeding to sustain growth and flowering.