Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Cannas Thrive In Hot Summer Weather
Cannas are prized for their large tropical foliage and showy, brilliantly colored flowers. The foliage is as ornamental as the flowers. Leaves may be green, greenish blue, coppery to purplish, ruby, or green with white stripes.
Cannas belong to the Cannaecae family and have leaves resembling bananas. They are tropical and sub-tropical perennials which flower year round in their native habitat. Modern cannas bear little resemblance to their ancestors. The cannas used in gardens today are mostly Canna generalis, not the old fashioned Indian Shot, Canna indica. Flowers range in colors from ivory, yellow, rose, salmon, crimson and red. Many characteristics also have been modified to make cannas more suitable for landscape planting. Dwarf cultivars grow only 1.8 feet in height while tall ones attain a height of 6 feet, with intermediate sizes in between.
Cannas thrive in fertile well drained, loamy soil rich in organic matter. Incorporation of manure or compost will help improve the soil in new flower beds. However, cannas will grow in almost any soil, provided good fertility and moisture is provided. Cannas are sun loving plants and perform best in full sun or semi shaded areas.
The rhizomes may be planted 1 foot to 2 feet apart, depending upon whether dwarf or tall cultivars are used. Addition of 1/3 cup of a complete fertilizer such as 10-10-10 for each rhizome and mixing it in with them planting soil will assure fast growth.
Cannas thrive under high summer temperatures. The only limiting factor in their growth at this time usually is lack of adequate moisture and fertilizer. In the absence of rain, water them generously twice a week. Cannas respond favorably to high fertility levels. Fertilize them with a complete fertilizer such as 10-10-10 at the rate of one pound per 100 sq. ft. on a monthly basis beginning in early spring to assure prolific blooms.
To assure continuous blooms throughout the summer, remove the part of the stem that bore flowers after the flowers have withered. Usually a second flowering shoot, growing from the node just below the terminal flower, will be halfway in bloom already. Remove this shoot when its blooms are withered. Another flowering shoot will soon develop on the node below the second shoot.
If spent shoots are not removed, energy will be used by developing seed pods, and the third flower cluster will usually remain dormant. If spent shoots are removed, energy will be directed to flower clusters on the third or fourth node to develop and bloom. If spent shoots are removed religiously, cannas can bloom profusely for a long time. When all flowering clusters on a stem finish blooming, remove the entire stem and leaves at or slightly above ground level. This will reduce the leafy appearance and will allow more light for other stems on the same clump. In addition, this will reduce crowding and competition for nutrients.
In our area, over wintering cannas is not necessary. However, the clumps should be rejuvenated to assure prolific growth and showy specimens for next year. Overcrowding, allowing the plants to set seed, and not removing the old stems, will cause cannas to decline after the first year.
Overcrowding or failure to rejuvenate the bed will result in few blooms, poor nutrition and the development of deficiency symptoms. Clumps should be dug on an annual basis, cleaned and old rhizomes removed and discarded. Spade up the entire clump and divide each clump. Discard those rhizomes that are old and do not contain eyes. Selected rhizomes should be cleaned off and rinsed in a bleach solution (1 part bleach and 9 parts water) to reduce the possibility of diseases that may infect the rhizomes. Cleaned rhizomes can be transplanted or repotted right away.
Cannas generally do not have the many problems so common to other annuals or perennials. Canna leaves are covered with a waxy substance that repels water. It is for this reason that diseases on cannas are rare even though the relative humidity and rainfall may be very high.
The most troublesome insects on cannas are grasshoppers and caterpillars. Heavy infestations will greatly detract from their appearance and reduce the cannas values as an ornamental plant. Carefully observation for chewing insects followed the appropriate control will insure beautiful plants all summer.
A problem frequently mistaken as insect damage is parallel tears in the leaves. This problem is not caused by insects but by water stress followed by an abundance of water. This can be prevented by periodically supplying water during dry spells.
Cannas should be seriously considered for home landscapes. Traditionally they have been grown in mass in formal or informal beds and borders, circles and squares in the center of lawns and gardens, parks and public places, where their colorful foliage provided interesting background material. They are not hard to grow, and can be easily grown year-round in south Florida. Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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