How to Grow, Cut, and Arrange Dahlia Flowers Like a Pro

There are tons of reasons to love dahlias, and their big, beautiful blooms are just the start. Similar to annuals, they'll bloom almost continually (and the more you cut them, the more flowers they'll produce), but like perennials, you can keep them alive to grow or replant year after year. There are thousands of dahlia varieties to choose from, and you can find blooms in almost every shade except blue. In a vase, they're also one of the longest-lasting cut flowers. Once you learn how to grow dahlias in your own garden, you'll have an almost constant supply of vibrant blooms throughout the summer.

How to Grow Dahlias

Plant dahlias in a spot that gets at least eight hours of direct sunlight a day. In dry, hot-summer climates, choose a spot that provides direct sun from the morning into midday, offering shade or filtered shade by the hottest part of the late afternoon.

Like potatoes, dahlias grow from tubers (they're actually edible) so good soil preparation is key. Loosen or dig soil to a depth of about 10 inches. Your soil should be easily worked and have good drainage. If you have heavy soil, amend with compost or aged manure. Planting is a good time to incorporate an organic fertilizer ($12, The Home Depot) with an N-P-K ratio of 5-10-15, 5-10-10, 10-20-20, or 0-20-20. The higher middle number, phosphorous, assists with bloom production, while the third number, potassium, helps root development. Any fertilizer recommended for vegetables can be used for dahlias.

Although you can start dahlias from seeds, it's easiest to use tubers. After you prepare the soil, dig a hole 4 to 6 inches deep, lay the tuber horizontally, and cover with soil. If you're planting several dahlias, grow the smaller varieties 9 to 12 inches apart. Taller dahlias can be spaced 2 to 3 feet apart, or half their final height (some can grow taller than 6 feet, so be prepared!).

Except in hot climates, don't water the tubers until the first shoots and leaves appear. Because the surface of the ground needs to stay warm (at least 60°F) for the tubers to sprout, avoid mulching until the plants are actively growing. Once the plants are established, add mulch to conserve moisture and prevent weeds. Because dahlia roots are shallow, pulling large weeds can easily disrupt the roots, so pull weeds only by hand when they're still small. Avoid using chemical weed controls and weeding instruments like hoes because they kill dahlia roots.

How to Stake Dahlias

Dahlia flowers can be 2 to 10 inches wide (the largest varieties are called dinner plate dahlias), so some will need extra support. Dahlias that reach 3 feet or taller should be staked to support the large, heavy flowers and keep plants upright in windy conditions. Position the stakes before planting so you don't accidentally drive them through the tubers.

You can use almost any sturdy material, such as bamboo or metal stakes or tomato cages ($6, Walmart), that will reach nearly the height of the fully grown plant. As the plants grow, tie them to the stakes using a soft material such as string, twine, or nylon stocking strips. Begin tying the dahlias when they reach 1 foot tall, and keep tying at 1-foot intervals.

Watering Dahlias

Once established, dahlias love water. They need deep watering at least two or three times a week with a soaker hose ($25, Walmart). When the plants are nearly a foot tall, add a nitrogen-soluble fertilizer every three or four weeks, following package directions, to promote plants with strong stems.

Growing Dahlias in Containers

Dwarf and small dahlia varieties can be grown in containers; just choose a large pot (12 inches or bigger) and give the plants extra fertilizer and water throughout the growing season.

Though they're high performers during warm weather, dahlias are susceptible to frost. In warm climates, the tubers can be left to overwinter in the ground, but in cold climates, leave the plants growing until they're blackened by a hard frost. Cut the stalks to about 6 inches, loosen the soil with a pitchfork to avoid damaging the tubers with a shovel or trowel, and wash the soil from the roots. Allow the tubers to air-dry.

Tubers should be kept cool (about 40-50°F) and dry during the winter months. They can be kept in sawdust, shredded newspaper, peat moss, or other materials that will keep them just slightly damp. If they're too cold or wet, the tubers will rot. If you don't want to save the tubers, you can always treat them as annuals and plant more every spring.

How to Cut and Arrange Dahlias

Dahlias are beautiful in the garden, but don't be afraid to snip a few for a vase; cutting dahlia flowers for bouquets actually allows the plant to produce more flowers. Be sure to deadhead any spent blooms, too.

The best time to cut flowers, including dahlias, is in the cool of the morning. Snip horizontally with clean pruners or scissors, taking stems long enough for your bouquet. Choose flowers that are open or nearly open because the buds will not open once they're cut. You should cut as much length as you need for your bouquet, but try to make the cut just above a set of leaf nodes and side buds. New shoots will grow from those nodes.

After you've harvested dahlia flowers, make a fresh horizontal cut at the bottom of the stem and place the cut ends in about 2 to 3 inches of very hot (not quite boiling) water. Let the stems stay in the water for at least one hour. This hot-water treatment conditions the stems so the blooms will last four to six days.

Once the cut stems have been conditioned, strip off all leaves that would be below the water line in your vase. This is true for all flower arrangements, not just dahlias. When leaves stay underwater, they decay and release bacteria that shorten the vase life of the flowers. Change the water in the vase every two or three days, adding a floral preservative to help the blooms last longer. Dahlias can be combined with other cut flowers to create beautiful effects, but dahlia arrangements are spectacular on their own.