The Dirt on Dahlias

Dahlias, the national flower of Mexico, are easy to grow and yield bountiful, beautiful blooms from mid-summer to the first frost. Their many shapes and riotous colors can brighten up gardens, borders, and even patio containers.

Dahlias require full sun, water, and fertilizer. Staking is important to prevent taller varieties from being toppled by strong wind or rambunctious pets. Dahlias are surprisingly disease and pest-resistant; however, they are browsed by deer.

Dahlias have tender tuberous roots that should be dug out every year after a hard frost and divided before being planted again in the spring. The clumps should be cut into sections with a sharp knife, making sure at least one eye or growing bud is included with each tuber. Eyes are found where the tuber joins with the stalk of last season's growth.

In the spring, after danger of frost has passed, it is time to plant the tubers. The hole in which the tubers are planted is the most important factor for the health and happiness of the dahlias. Dig it deep and wide in a sunny, well-drained location, and amend it with well-composted manure. Stagger the holes far enough apart to allow for good air circulation and space to work around the plant.

Plant the tubers four to six inches deep with the eyes heading upwards and cover with soil to ground level. Label with information about the variety on a waterproof tag and attach it to a stake next to the hole.

When the plant is about one foot tall and displays three to four pairs of leaves, pinch the terminal (top) shoot to encourage branching. Although one pinching is sufficient, additional pinching will make the plant even bushier with more blooms. For larger single blooms, remove the two side buds on each branch when they are pea-sized, leaving only the central bud to grow.

Summer care is minimal. Because dahlias are fast growing, they need plenty of water. The ground should be moist, but not saturated. Monthly fertilization with a low nitrogen fertilizer such as 5-10-10 or 5-20-20 is recommended, as dahlias are heavy feeders. Deadheading spent flowers encourages further blooming.

After a killing frost blackens the plants in the fall, cut the stems back to six inches while still in the ground. This stimulates the tuber to produce the eyes that will develop into a new plant. Because the stems are hollow, it is a good idea to cover the top with some aluminum foil to prevent rain from rotting the roots. Wait four to eight days for the eye to develop, and then carefully dig each clump with a spading fork, gently removing excess dirt.

Turn the plant upside down to drain and allow it to cure for a few days. It is a matter of personal preference whether tubers are divided in the fall or in the spring when the eyes have begun to sprout.  Place tubers in a wood, cardboard, or plastic container and cover with vermiculite or wood chips (pet bedding works well). Alternatively, wrap them in several sheets of newspaper and a piece of a plastic tablecloth or butcher's paper.

The key to dahlias' winter survival is storing them at temperatures between 32 and 50 degrees to prevent disease and rot. Warm temperatures also prompt the tubers to develop sprouts too soon. Mark each tuber with indelible ink or tag it with masking tape.

The high point of growing dahlias is enjoying the flowers. With a little tender loving care, dahlias will provide summer-long color in your garden and showy blossoms for your vases.