Canna lilies are dramatic, tender perennials that bring a striking tropical feel to any garden with their vibrant flowers and large, banana-like foliage. These impressive plants grow from underground stems called rhizomes, not true bulbs, and flower prolifically from mid-summer until the first frost. Ensuring the rhizome is planted at the correct depth is a fundamental step that directly influences the plant’s emergence, health, and bloom production. Proper planting technique is the first factor for cultivating these heat-loving garden features.
Preparing the Planting Site
Canna lilies thrive best in locations that receive full sunlight for at least six to eight hours each day, which encourages the most abundant flowering and vibrant leaf color. Planting should be timed carefully, waiting until all danger of frost has passed and the soil temperature has warmed consistently to at least 60°F. Planting into cold soil can cause the rhizomes to sit dormant or rot before they have a chance to sprout.
The soil itself requires preparation to support the Canna’s vigorous growth and moisture needs. These plants prefer organically rich, moist, and well-drained soil with a slightly acidic to neutral pH between 6.0 and 6.5. Before planting, the soil should be loosened to a depth of about one foot. Several inches of compost or well-rotted manure should be mixed in to improve fertility and drainage, as Cannas are heavy feeders requiring substantial nutrients.
Determining the Correct Planting Depth
The most common recommendation for planting Canna rhizomes is to place them so that they are covered by one to two inches of soil. This shallow depth is crucial because it allows the new shoots to reach the surface quickly and begin photosynthesis, while still providing enough insulation for the rhizome. Some sources suggest a slightly deeper four-inch depth, but a shallow planting of one to two inches of soil above the rhizome is generally safer, particularly in cooler climates where soil warming is slower.
The rhizome must be set horizontally in the planting hole with the “eyes” or growth points facing upward. These eyes are the nodes from which new stems will emerge, and orienting them correctly ensures the shoot grows directly toward the soil surface. Planting too deeply (four or more inches down) can delay shoot emergence significantly or cause the rhizome to expend too much stored energy, potentially leading to rot. Conversely, planting too shallowly leaves the rhizome vulnerable to drying out or becoming unstable as the plant grows tall.
Spacing is an important consideration for mature growth, as Cannas can become quite large. Smaller cultivars should be spaced about 18 inches apart, while the tallest, most vigorous varieties may need up to three feet of space between them for adequate air circulation and root development. For container-grown Cannas, plant the rhizome at the same shallow depth, ensuring the pot is at least 18 inches in diameter to accommodate the expansive root system.
Immediate Steps After Planting
Once the rhizome is placed and covered with soil, water the area thoroughly. This initial deep watering hydrates the rhizome and settles the surrounding soil, eliminating air pockets that could cause the roots to dry out. After this first soaking, withhold regular watering for the first two to three weeks until the first shoots emerge, as excessive moisture before growth starts can promote rot.
Following the initial watering, apply a layer of organic mulch, such as shredded bark or compost, to the soil surface. This mulch layer helps conserve soil moisture by reducing evaporation and regulates soil temperature, keeping it consistently warm. If the soil was not heavily amended before planting, a slow-release granular fertilizer formulated for flowering plants can be spread around the planting area to provide nutrients. Shoots can be slow to appear, often taking several weeks, so patience is necessary as the rhizome first establishes its root system before sending up foliage.