The Master Gardener Articles

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Summer Flowering Bulbs

Summer flowering bulbs can add beauty to your landscape when other bulbs have faded with the heat of summer.  These bulbs, in contrast to spring flowering bulbs must be removed in the fall since freezing will destroy the bulb.  If you are willing to remove the bulb for future plantings or buy new summer flowering bulbs each spring, read on.

In Central Ohio, there are 5 species which are classified as summer flowering plants (bulbs, rhizomes, tubers or corms collectively referred to as bulbs).

Tuberous begonias have a large camellia type flower coming in various colors.  Plant the tubers in a peat moss/perlite mix or a good commercial potting mix with good soil drainage in early April. Keep at 60 – 75°F until pink shoots start to grow then move to a sunny area. Keep moist, but not wet and fertilize every 2 weeks. Do not use a fertilizer containing ammonium  salts which will cause crinkled and curled leaves to occur. After frost has passed (Memorial Day) plant in a semi-shaded area and stake.  Continue to fertilize on a bi-weekly basis with a liquid fertilizer.  Place plants 12 inches apart to provide good air movement, which should suppress diseases.

Canna rhizomes produce flowers on stems 3 to 8 feet tall and range in color (red, pink, yellow, orange and cream color). If you miss a Mid-March planting indoors, you can plant them directly into the garden in Mid-May. The plant site should be well drained and in full sun. Peat moss or compost (1/3 to 2/3 native soil) is recommended as an amendment space 18 – 24 inches apart and plant to a depth of 3 times the diameter of the rhizome. Apply a complete fertilizer as the shoots emerge, using a high phosphorus fertilizer (e.g. 5-10-5) at the rate of 3-4 pounds/100 square foot or ½ oz. square foot (1 tablespoon) every month. Stake plants, if necessary. In the heat of summer, water more frequently as soils becomes dry. Remove dead flowers to encourage more flowering.

Caladium tubers produce bright bold leaves of red, pink, green, white and bi-colors. The flowers are insignificant. These should be started indoors in early March using a commercial potting mix, plant 2 inches deep with bottom heat (75 - 80°F). After the last frost (Memorial Day) move plants to a protected area (shady and wind-protected). Water as needed especially on hot summer days.

Dahlia tuberous roots produce plants 2 to 8 feet tall with flowers 8-12 inches across. A wide range of colors except blue are available. Plant the tubers directly in the garden in Mid-May in a well drained, sunny location. Stake at planting time and feed lightly (one teaspoon of a 5-10-5 per plant). As the plant grows, up the rate to 1 tablespoon per plant using a 5-10-5. For maximum flower size, prune the side stems allowing only one main stem to develop. Mulch plants after establishment to conserve moisture and keep the soil cool. Dahlias are prone to aphids, spider mites, leafhoppers, stalk borers, virus and wilts, so be on the alert.

Gladiolus corms produce flowers in a wide range of colors and range in size from 1 to 5 feet. Plant corms outdoors over a 2 month period starting in early May. This will stagger the bloom period.  Plant the corms 4 inches deep 6 inches apart in a well drained sunny location. Use a 5-10-5 fertilizer (1 tablespoon per square foot) at planting time and again as the flower spike develops. Stake as needed. Harvest flowers but leave at least 4 leaves on the plant to restore the corm. Thrips can be a real problem. Check with your local nursery or hardware store for insecticides.

Storage of these “bulbs” generally can be accomplished after the frost has killed the tops. Remove the bulbs from the soil, detach the dead top, air dry for 1-2 weeks, clean off the soil and place in peat moss or sawdust at 40 - 50°F. Do not allow bulbs to freeze. Caladiums and Dahlias should be stored at a higher temperature (60 - 70°F).

For more information on this subject, see the web site http://www.ohioline.osu.edu and search for the fact sheet HYG-1244-92 (Summer Flowering Bulbs) or call the Union County Extension Office at 937.644.8117 or toll free (Union County Residents Only) 800.859.8584 or e-mail George McVey at gmcvey@ag.osu.edu.