The care information provided in this section represents the kind of practical advice is available for all the plants in this web site if you subscribe to the monthly customized newsletter Yardener’s Advisor.
Before planting, drive stakes to support all but dwarf varieties. Tie the growing plants to these stakes as they grow. Pick off faded flowers. To encourage extra large flowers, leave the bud at the end of the stem, but pinch off 2 to 4 pairs of leaves and associated buds and side branches growing below this terminal bud. For bushier plants with more flowers, pinch out the central stem after 4 to 6 leaves form, so many side shoots will develop. Plants will also bloom best if you thin dense growth to permit better lighting.
Dahlias need at least 1 inch of water a week from rain or from a watering system. If your plants haven't gotten 1 inch of water during the week, check soil moisture under the mulch to see if you need to water. Use a sprinkler or soaker hose for gradual penetration to a depth of 10 to 12 inches. Don't allow dahlias to dry out. If they cease to flower, it is difficult to get them to resume for the rest of the season. For information on products see the file on Choosing Watering Equipment
Give dahlias a good start by adding a tablespoon or so of slow release all-purpose granular fertilizer to the soil you plant each tuber in. When the growing plants have leafed out, as the season progresses, sprinkle another tablespoon on the soil around each plant. Do not get the fertilizer on the foliage. Some serious gardeners spray a dilute solution of liquid fertilizer on the foliage of their plants once or twice during the growing season to invigorate them. This is not essential.
Mulching and Weed Control
Since dahlias are particularly fond of moist soil, mulching is important. Spread a 3 to 4 inch layer of an attractive organic material like chopped leaves, wood chips, shredded bark, or dried lawn clippings on the soil around the base of each plant. This not only will conserve soil moisture, but it will discourage weeds and keep soil from splashing up on the flowers when it rains. For more information see the file on Using Mulch
Dahlias are ideal cut flowers. All the varieties are gorgeous in either informal bouquets or formal arrangements. Cut them when the flowers are fully opened. Store them overnight in a bucket of cold water in a cool room. When you transfer them to their container, strip off from the stems all leaves that would fall below the water line to keep the water clean and bacteria-free. Cut dahlias will last 7 to 10 days. For more information see the files on Keeping Cut Flowers and Cut Flower Supplies
It is possible to acquire more dahlia plants several ways. Experienced gardeners, who have patience, may start some kinds of dahlias from seed or purchase flats of seed-grown plants. These will make small tubers by the end of the growing season, which must be dug up and stored over the winter (see below). The easiest way to get more dahlias is to divide the tubers of the ones dug up at the end of the season. Do this either in the fall or the spring. Prior to killing frost in fall, cut off their foliage and dig the tubers from the ground, being careful not to damage them. Gently brush off any attached soil, and dry them. Divide them by cutting them with a sharp knife so that each piece of tuber has a piece of stem. Dip the cut ends in a mixture of agricultural lime and garden sulfur to repel insects and diseases. (Dividing could be done in spring instead.)
Since dahlias are not hardy in northern regions they must be dug from the soil and stored over the winter. At first hard frost the tops will be frozen and blackened. After this happens, cut the stalk to within 6 inches of the ground and allow the plants to remain for a week to 10 days to cure and become dormant. Dig them as described above; using a garden fork is the best way to avoid damage. Divide them immediately or wait until spring. Pack the tubers in moist sand, peat moss, or vermiculite and store them in a cool (35° to 50°F.), slightly humid place. Check moisture levels occasionally. They must not dry out, nor may they be allowed to become too damp and risk disease. Three weeks before planting time, put the container of moist tubers in a warm place so that the eyes (buds) in each tuber can start growing. Discard those that don't sprout.