Peffley: Dahlia is ornamental that blooms all summer

The dahlia is an ornamental that blooms all summer and is an excellent performer in the cutting garden.

The scientific name of the garden dahlia is Dahlia hortensis but it is correct to use its common name “dahlia.”The International Registrar holds a list of the 18,000 cultivars of registered dahlias (dahliaworld.co.uk).

Dahlias are a floriferous addition to the garden with varieties in a kaleidoscope of colors. There are an astonishing 50,000 dahlia types that are classified into distinct groups by form of their inflorescences and color.

The forms have descriptive names such as Ball, Cactus, Formal and Informal Decorative, Pompon, Peony and Orchid. Cultivars in each of these forms can be colored bronze; dark or light pink; dark red; flame; lavender, lilac or mauve; orange; purple, wine and violet; white, and yellow.

A rather complicated method used to determine whether a bloom is variegated, a blend or is bicolored can be found on dahlia.org.

New cultivars of dahlias are propagated from seed. They are easily hybridized, which is evident in the huge number of varieties. For most gardeners, however, a dahlia planted from tubers is the most reliable method of obtaining plants.

Tubers should be planted when the soil warms after the last frost. I have planted tubers as late as mid-June and still had blooms before the autumn frost.

Dahlias need to be planted in soil with good drainage and they do not require heavy watering. Too frequent or excessive waterings lead to root rot, one of the most common conditions for dahlia plant death.

Place tubers several inches deep with ‘eyes’ pointing up. The eyes are the growing points for shoots. If several dahlias are being planted, place tubers at least 2 feet apart to provide adequate air movement around the plants.

Dahlia blooms are heavy and require support to keep plants upright. For bloom support plants can be either grown in tomato cages, tied to stakes or use wire supports. Tomato cages work fine by guiding shoots through the wire as they grow.

If tying, use wide plastic tape to secure the lower segment of a bloom stalk to a stake and make several more ties up the bloom. Continue taping for each flower stalk as spent blooms are removed. Using wire heavy bloom supports may be preferred because they give a cleaner look without cages, stakes and tape.

These are the same wire supports that are used for peonies. Move the supports from spent peonies to the dahlias, where they will stay all summer.

The American Dahlia Society awarded the largest bloom in 2016 to a 14.375-inch entry.

Professionals use the technique of disbudding to force larger blooms. Each branch of a dahlia’s flowering stalk has three blooms with the middle bud first to open. To disbud, remove the outer two buds. A second strategy is to remove some of the side shoots. This is a good strategy to obtain long-stemmed blossoms for tall vases.

Note: Some information from the American Dahlia Society.

ELLEN PEFFLEY taught horticulture at the college level for 28 years, 25 of those at Texas Tech, during which time she developed two onion varieties. She is now the sole proprietor of From the Garden, a market garden farmette. You can email her at gardens@suddenlink.net.