Gardening: Dahlias, in varying shapes, sizes and colors, are delightful landscape additions

Dahlias, the national flower of Mexico, are easy to grow and yield bountiful beautiful blooms from mid-summer through first frost. Their many shapes, sizes and riotous colors will brighten up any garden, border or patio container.

Dahlias are native to the mountainous region of Mexico and were discovered by Swedish botanist Anders Dahl. Native dahlias are single-type dahlias about 3 inches in size while improved cultivars are now available with flowers up to 16 inches across and in shades of nearly every color except green, brown and true blue.

Planting tips

Dahlias grow best in locations with full sun and rich, well-drained soils with a pH of about 6.5. Their tuberous roots will quickly rot in poorly drained soils. Compost or sphagnum peat moss can be added to the planting hole to provide nutrients and organic matter.

Dahlia tubers should be planted horizontally in the soil with the crown just above the soil level when the soil has warmed to a minimum of 55 degrees Fahrenheit. Smaller flowering dahlias, which are typically three feet tall, should be planted two feet apart.  Larger flowering dahlias should be planted three feet apart.

Larger flowering dahlias will require a stake or trellis for support as the plant matures. It is best if these supports are installed at planting or when the plants are small. Stakes should be approximately five feet tall and stems should be tied loosely to the stakes as the plant grows. Dahlias have shallow roots so be careful when cultivating around plants.

Summer care

In very early July, dahlias should be mulched with well-aged compost, aged manure, peat or straw. Dahlias should be watered regularly when rain is insufficient. Be sure to water the soil, not the foliage to reduce the incidence of foliar diseases. A monthly application of fertilizer will encourage large blooms. If a granular fertilizer is used, be sure to water it in thoroughly after application. Fertilization of dahlias should cease in late August.

Dahlias make great cut flowers for use in vases and arrangements. Cut flowers when they are fully opened and before the tips of the flowers begin to dry out or brown. Early morning cutting will provide the longest-lasting cut flowers.

Fall digging

Dahlia tubers can be dug in the fall and replanted in subsequent years if handled and stored properly. Dahlias should be lifted after the first killing frost or before the end of October. Cut the foliage three to four inches above the soil level. Because tubers may have spread quite a distance, begin digging far enough from the crown of the plant so they are not cut or damaged. Once the tubers are out of the soil, remove as much soil as possible to allow the soil to dry.  When dry, remove the remainder of the soil.

Dahlia tubers should be stored in containers lined with a few inches of peat moss, sawdust or vermiculite, and covered to their crowns with the same material. Boxes should be stored in a dry location with a temperature of 40 degrees to 55 degrees. Tubers can be potted indoors in March or April and transplanted in late spring or planted directly in the ground after the danger of frost has passed.

The Greater Columbus Dahlia Society conducts dahlia programs and events for members of the society as well as the public. The society will hold its annual Dahlia Show on Sept. 4-5 at the Marysville YMCA, 1150 Charles Lane, Marysville. The show will feature hundreds of spectacular blooms on display by growers from throughout the Midwest. For more information go to: columbusdahlias.com.

Mike Hogan is an associate professor at Ohio State University and an educator at the OSU Extension.

hogan.1@osu.edu