Answer: Last year's leaf browning and lack of flowering was probably due to drought stress or overcrowding, says Carl Van Staalduinen, canna specialist at Terra Ceai Farms, wholesale growers of 15 acres of cannas in Pantego, North Carolina. Last summer was very hot and dry in this area. If cannas are stressed for water especially in July, while the flowers are forming the leaves will turn brown and the buds will abort, he says. To get cannas to bloom, water them regularly, says Van Staalduinen. Theylike full sun and a well drained, humus soil that is consistently moist. Water the cannas so that the soil is moist to a depth of six inches every few days during hot, dry conditions. Another possibility is that the rhizomes are overcrowded, says Van Staalduinen. If the stalks are spindly, that's a sign of overcrowding. Actively growing cannas may need to be divided every three to four years, he says. In spring, lift and divide the rhizomes, making sure each section has two to three eyes. Replant the sections, covering them with one inch of loose soil, and apply a complete fertilizer such as 10 10 10. Don't mulch the plants, however. If the rhizomes are buried too deeply underground, flowering is limited, he explains.
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