If you plant dahlias in well-draining soil located in full sun they will reward you with colorful blooms from July until the first frost of fall. These easy-care flowers perform their best during the hot, dry days of July and in September and October when most other flowers wilt by the wayside. Dahlias are hardy in zones 8-10 and come in a wide variety of bloom colors and heights, making them a perfect choice for any home garden.
Dahlias are sold in the spring as tubers or bedding plants. Tubers can be started indoor in planters, then transplanted outdoors to get a head start on the growing season. Select a sunny location and work some compost into the soil to ensure good drainage. After all danger of frost has passed, plant tubers three inches below soil surface and place bedding plants at the same level they were at in their container. Cover with soil, water in well and apply a layer of mulch to control weeds and retain moisture.
Dahlias need minimal after-care, but do appreciate a little food and support. Apply a balanced fertilizer (10-10-10) at spring planting time then again at the start of bloom time in July. Water only during times of prolonged drought and the plants begin to wilt.
Some varieties of dahlias can reach a mature height of 5 feet, any variety over 3 feet will need some support. Use tomato cages, bamboo stakes, trellises, etc. to help these tall beauties stand up straight. Dahlia blooms range in size from petite pom-pom type blooms to wide open, saucer-sized blooms and all make excellent cut flowers.
Dahlias are perennials, but can be treated like annuals and replaced each year. If you want to save some garden money, dig up the tubers and plant them over and over again.
At the end of fall, before the soil freezes but about 2 weeks after the first killing frost, dig the tubers up. Cut the stems back to 6 inches and gently rinse the soil off each tuber.
Lay tubers in a single layer on spread-out newspaper to dry for 24 hours in a location where they won’t freeze.
If you have more than one variety of dahlia, use a permanent marker to label each tuber. Place clean, dry, labeled tubers in a cardboard box and cover with peat moss or vermiculite and store in cool, dark place until next spring.
Divide tubers in spring just before planting. Use a pair of sharp hand-held pruning shears and cut small tubers off of the large clump. Each tuber must have an ‘eye’, which is a small knob where it had been connected to the main stalk.
American Dahlia Society