Canna lilies are tropical plants valued for their vibrant flowers and bold foliage, bringing an exotic feel to any garden space. These vigorous plants thrive in summer heat. Achieving a continuous display of blooms throughout the growing season requires a focused maintenance strategy. Gardeners must manage spent flowers, provide consistent energy through nutrients and water, and mitigate common environmental threats. This encourages a steady succession of new flower spikes until the first frost.
The Technique of Deadheading for Rebloom
Promoting continuous flowering relies heavily on deadheading, which redirects the plant’s energy away from seed production and toward producing new growth and flowers. Canna lilies produce multiple flower spikes on a single stem, so deadheading occurs in two stages. The first step is to carefully remove individual spent blooms as they wilt. This prevents the plant from expending resources on forming seed pods and allows unspent buds on the same stalk to continue opening.
Once a flower stalk has completely finished blooming, the entire stalk must be cut down. Using a clean, sharp tool, remove the spent flower stalk just above the nearest healthy set of leaves or near the ground. This signals to the rhizome—the underground stem—that it needs to generate a new shoot. The new shoot will then develop a fresh stalk and subsequent flowers, ensuring a cycle of continuous rebloom.
Essential Nutrient and Water Management
Sustaining the energy required for continuous flowering demands a regular feeding regimen, as cannas are heavy feeders. A fertilizer lower in nitrogen (N) and higher in phosphorus (P) and potassium (K) is preferred to encourage blooms over excessive foliage growth. A ratio such as 5-10-5 is often recommended, though a balanced 10-10-10 formula can also be used. Applying a granular fertilizer monthly throughout the active growing season provides the nutrients necessary to fuel the development of new flower spikes.
Consistent moisture is equally important because the plant halts flower production during drought. Cannas thrive best in consistently moist soil conditions, but they do not tolerate being waterlogged, which leads to root rot. During the hottest parts of summer and dry spells, deep watering is necessary, aiming to provide one to two inches of water per week. Dehydration quickly stresses the plant, causing it to conserve resources by sacrificing new blooms.
Troubleshooting Environmental Stressors
Even with optimal feeding and watering, environmental factors can occasionally cause blooming to cease or slow down. One of the most common threats is the presence of spider mites, which are tiny pests that thrive in hot, dry conditions and can stress the plant enough to inhibit flowering. These pests are often identified by fine webbing on the leaves. They can be managed by thoroughly spraying the affected foliage with insecticidal soap or a mixture of alcohol and water. Maintaining adequate irrigation is a strong preventative measure, as water-stressed plants are more susceptible to damage from spider mites.
Extreme heat waves can also temporarily interrupt the flowering cycle. While cannas love full sun and warmth, intense afternoon sun can cause the foliage to scorch and the plant to enter a temporary dormancy. If a prolonged heat dome is expected, providing temporary afternoon shade or increasing the frequency of watering helps mitigate the stress. Once conditions become more favorable, the plant will resume its production of new flower spikes.