Why Would a Canna Lily Not Bloom?

Growing Conditions

• Short growing seasons and freezing temperatures make severe demands on the genetic structure of cannas. If plants encounter freezing temperatures in spring, they stop growing and foliage dies. Once the temperature and soil warm, the plants resume growing. Resilient cannas can die back and start growing again several times. Inflorescence, or flowering, only begins when the plant is mature enough and has enough leaf surface to provide the energy needed. In northern zones with shorter growing seasons, frozen ground in winter kills tubers and late spring warm-ups limit bloom. In areas where frost is a problem, potting tubers on a sunny windowsill expands the growing season. Canna tubers that have dried out in storage or been stored below 45 degrees Fahrenheit may also grow foliage but fail to bloom.

Location

• Cannas need full sunlight. Hybrid cannas with their large, reblooming flowers, need summer warmth and at least four to six hours of full sun to bloom. Cannas planted in too much shade may not bloom or bloom poorly, particularly in areas with cool summers. Moving plants to a location with more sun exposure is advisable, especially in northern zones where spring potting may also help provide enough seasonal warmth for flowering.

Soil

• Although several native cannas grow in water or marshy areas, garden cannas require moist, well-drained soil and struggle in soil that is dry. Spring rains that waterlog soil and rot roots also retard the growth and may affect flowering. Starting plants in pots and placing them on a sunny windowsill where moisture levels are easily controlled keeps them healthy until spring sogginess dissipates in the garden. Frequent watering of dry soil -- or an alternative planting site -- keeps cannas growing and blooming. Tubers planted deeper than 4 to 8 inches may not bloom well.

Nutrients

• Cannas grow best in loamy soil, enriched with between 1 and 2 inches of well-rotted manure incorporated before planting, advises the University of Florida's Robert J. Black. General 10-10-10 garden fertilizer given mid-season, says master gardener Cynthia W. Mueller, is all that most cannas need, but too much nitrogen may encourage foliage growth at the expense of flowering. A soil test, completed after addition of soil amendments, should reveal whether phosphorus or potassium, the two major nutrients that support flowering, is needed. Even well-nourished cannas will not bloom well, however, if they are crowded next to their neighbors. Thin out the plants as needed.