Canna lilies are tropical flowering plants known for their bold foliage and vibrant, summer-long blooms. These plants grow from underground storage organs called rhizomes, which are similar to bulbs. Because cannas originate in warm climates, their cultivation in Ohio’s USDA Hardiness Zones 5b through 7a requires specific timing and care to manage cold winters. The soil temperature, not the calendar date, dictates when they can be safely planted and when they must be lifted for winter storage.
Optimal Timing for Outdoor Planting in Ohio
Planting canna rhizomes directly into the garden should not occur until all risk of spring frost has passed and the soil has sufficiently warmed. In Ohio, this window typically opens around mid-to-late May, depending on the specific zone and microclimate. The requirement for successful growth is a soil temperature that consistently measures at least 60°F (15°C). Planting into cooler soil risks the rhizomes rotting instead of sprouting, as they are highly sensitive to cold, damp conditions.
Gardeners should use a soil thermometer to confirm the temperature at a two-inch depth before planting. Waiting for the soil to warm naturally ensures the rhizomes have the heat necessary to break dormancy and begin growth. For earlier summer color, start the rhizomes indoors four to six weeks before the last expected frost, usually beginning in mid-April. This head start allows the plants to develop foliage and roots in a controlled environment, making them ready for transplantation outdoors once the soil is warm enough.
Preparing and Planting the Canna Rhizomes
Once the soil is warm, selecting the proper site is the next step. Cannas must receive full sun exposure for the majority of the day to ensure vigorous growth and abundant flowering. A location receiving less than six hours of direct sunlight often results in leggy plants with reduced bloom production.
Cannas thrive in rich, well-draining soil that is kept consistently moist. Before planting, amend the soil with organic material, such as compost or well-rotted manure, to improve fertility and drainage. The rhizomes should be planted four to six inches deep, oriented with the “eyes,” or growing points, facing upward.
Proper spacing is necessary to allow the large foliage to develop and promote air circulation, which helps prevent fungal diseases. Space the rhizomes about 18 to 24 inches apart, depending on the expected mature size. After placing the rhizomes, cover them with soil and water the area thoroughly to settle the medium and initiate growth.
Essential End-of-Season Care and Storage
Because Ohio winters drop far below freezing, canna rhizomes cannot be left in the ground and must be dug up for storage. The best time to lift the rhizomes is after the first light frost, typically in late October or early November, but before the ground freezes solid.
A light frost signals the plant to enter dormancy and causes the foliage to die back, redirecting energy into the rhizomes. After the foliage is killed by frost, cut the stems down to two to six inches above the soil line. Use a garden fork or spade to carefully loosen the soil around the rhizomes to avoid damaging the storage tissue.
After lifting the clumps, gently remove the loose soil. The rhizomes must then be cured for several days to a week in a well-ventilated location at warmer temperatures, ideally between 70°F and 80°F. This curing process hardens the outer layer and helps prevent rot during storage. Once cured, store the rhizomes in a cool, dark, and moderately dry location where the temperature remains consistently between 40°F and 50°F.
The rhizomes should be packed in a medium that provides ventilation and absorbs excess moisture, such as peat moss, dry sand, or wood shavings. Avoid using airtight containers, which can trap moisture and promote decay. Check the stored rhizomes periodically throughout the winter months. If they appear shriveled, lightly mist the packing medium; if they are too moist, air them out for a few days before repacking.