Dahlias are popular additions to many gardens because of their versatility. They do well in gardens as bedding plants and as specimen plants in containers. Dahlias also make excellent cut flowers. In my opinion, there is nothing more impressive at a flower show than the large "dish plate"-sized dahlia flowers. Their flowers display a variety of sizes, shapes, and colors.
There are both single-flowering and double flowering types. Double-flowering dahlias include cactus (tubular petals that curve backward for more than half their length), semicactus (similar to cactus except the petals are broad at their base and curve for less than half their length), decoratives (broad pointed or rounded petals, irregularly arranged), ball (ball shaped flowers over 2 inches in diameter), and pompons (ball shaped flowers less than 2 inches in diameter).
Fully grown dahlia plants range from one foot tall to over six feet in height. They may be bushy and filled with clusters of miniature or medium-sized flowers, or they may have two to four stalks bearing one to several very large blooms on each. The flowers measure from less than 2 inches to more than 8 inches in diameter. Colors range from pure white and pastel tints to bright shades of red, yellow, orange, red, and purple.
Dahlias can be started from seed, rooted cuttings or dormant tuberous roots. Although dahlia seedlings are not difficult to grow, they do require 12 to 14 weeks before they bloom. Thus, it's a good idea to start dahlia seeds indoors in March to have adequate sized plants for May planting. Most gardeners find it more convenient to purchase plants or tuberous roots.
Dahlias should be planted in a well ventilated, sunny location that is protected from strong winds. Plant dahlias after the danger of spring frost is past. To plant the tuberous roots, dig a hole 6 to 8 inches deep and large enough to accommodate the root. Lay the root flat with the bud or growing point up and cover the root with 2 inches of soil. Continue to fill in the hole as the plant grows. Place a stake 6 inches away from the root of the tall growing varieties at planting time. This is important because the central stem of the plant will need to be supported as it grows. When the plant is about a foot tall, tie it loosely to the stake. Continue tying the stem to the stake as the plant grows to insure an upright plant with straight branches.
Dahlias respond to deep and frequent waterings. Dahlias require approximately an inch of water (either rainfall or irrigation) each week throughout the growing season. In hot, dry weather watering should be done at three-day intervals during the blooming season. Because dahlias are heavy feeders, they will respond to one or two sidedress fertilizer applications during the growing season. The first application should be made shortly after the sprouts emerge and the second in late July. Apply a 5-10-10 fertilizer at the rate of 1/4 cup sprinkled in a ring around each plant. Work it into the soil and water in well. Avoid getting fertilizer on the foliage.
You can increase the size of dahlia blossoms by removing lateral buds from the large-flowered varieties. This is called "disbudding." When the three buds that form at the end of each branch reach the size of small peas, remove the two side buds. The center bud will then develop into a larger blossom. Small-flowered dahlia plants should not be disbudded. Dead flowers should be removed from all dahlia plants to encourage repeat bloom.
Dahlias are not winter hardy in Iowa. If a gardener wants to keep them from year to year, the roots must be dug and stored indoors for the winter. By the end of the growing season the single root that was planted in the spring will have developed into a clump of roots. This clump of roots needs to be dug after the first killing frost. Cut the stems off 2 to 3 inches above the soil. Using a fork, lift the clumps gently, and shake off the excess soil. Lay them upside down on the ground to allow them to dry for a few hours. Do not wash the soil from the roots. Store the clumps in boxes of peat moss or vermiculite in a cool, dry place where the temperature does not drop below 32oF. Check them occasionally during storage and remove those that show signs of rot. It may be necessary to add a little water to the vermiculite if the roots begin to shrivel.
Prior to planting next year, divide the clumps carefully with a sharp knife. Be sure that a piece of the crown with an eye (bud) is connected to each root. Roots without an eye will not grow.
This article originally appeared in the July 1, 1992 issue, pp. 1992 issue, pp. 118-119.