Though they appear very tropical, cannas can be grown almost anywhere in the United States. They are reliably cold hardy in USDA climate zones 8 through 10, but can be grown as annuals or lifted and stored over winter in cooler zones. Where cannas are not cold hardy, they may be started indoors in containers during the months of February or March and planted outdoors when danger of frost is past. This will give them a head-start so flowers can be enjoyed before mid-summer.
Cannas prefer full sun but will tolerate partial shade with a minimum of four hours of direct sun per day. Rich soil, moist but well-drained, is best with mildly acidic pH ranging from 6.0 to 6.8. They are not too picky, though. I've seen them doing quite well in ditches and at the edges of ponds. The best way to determine if the pH is within range and contains the proper nutrients is to have the soil tested. Your local Cooperative Agricultural Extension Service can help you. You can collect the soil sample yourself. For a nominal fee, they will send your soil sample to a laboratory for analysis. Be sure to call the Extension office for instructions.
Cultivate the soil to the depth of 10" and add plenty of well-rotted compost. Remove weeds and debris. Soil test results may recommend other soil amendments. Follow those instructions. The soil amendments you may use depends upon the type of soil you have in need of amending. Common soil amendments include sulphur for lowering pH, limestone for raising pH, sand for helping drainage, clay for slowing drainage, gypsum for breaking up caking clay and compost for enriching the soil. Bone meal is especially good for rhizomes. Which you should use depends upon your particular circumstance. If you use synthetic fertilizer, allow at least a week before planting so it can be incorporated into the soil by rain or irrigation and not burn the rhizomes.
Plant your cannas in spring after the danger of frost has passed. Planting holes or trenchs should be about 4" deep. Space the rhizomes or plants 12" to 18" apart. Lay them flat in the bottom of the hole or trench. Don't worry about which side is up. Cover with about two inches of soil. Water deeply. If some of the soil washes away, add more. Avoid heavy watering until new shoots grow to 4" height.
During summer, you may fertilize occasionally. Apply 2 tablespoons of 10-10-10 fertilizer per ten square feet of garden area every two weeks until flower buds appear. Do not allow synthetic fertilizers to come into contact with the plants. Irrigate if rainfall is inadequate. About one inch of water per week should be sufficient. When you water, do so deeply in order that moisture will reach the roots. Weed when necessary. A light mulch of straw will help to preserve moisture and suppress weeds. Other than that, very little maintenance is needed. Though it is not necessary to remove spent flowers, doing so will prevent seed from forming and may encourage a longer bloom period. Occasional application of a recommended insecticide will keep away leaf-eating insects such as Japanese beetles, though the extent of their damage is usually minimal and cosmetic. Call your Cooperative Agricultural Extension Office for insecticide recommendations. Always, follow label instructions.
Shorter growing cannas are wonderful in container gardens. Use the finest potting soil; cheap soil will give poor results. The best potting soils will be light-weight, peat-based with added materials to enhance plant growth. Select containers that will allow you to include companion plants, if desired. Larger containers will require less frequent watering. The addition of water retentive gel can be beneficial. Plant the rhizomes at the proper depth.
If yours is a climate where cannas will not survive the winter, you can dig and store them for planting next year. At the end of the season following the first hard frost, lift them, cut off stems and leaves and wash the rhizomes. Large ones may be divided with each piece having three or four "eyes." "Eyes" are growing points resembling buds where future growth will appear. Pack in peat moss and store in boxes or bags with some ventilation. Plastic bags with ventilation holes like potatoes come in will do nicely. Store in a dark place where the temperature can be maintained between 45 and 55 degrees F. Moisture should not collect in the storage container. On the other hand, the rhizomes should not be allowed to dry out.
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