Dahlias, grown for their beautiful flowers, come in all colors except the elusive blue. They bloom nonstop from summer until frost in a variety of shapes and sizes. As cut flowers, they will last several days, making them excellent for homegrown bouquets. 

A few of the most exciting dahlia types include the cactus form with its needlelike petals and the ball (or pompon) with small, spherical blossoms. Dinner plate dahlias have enormous blooms; some measure nearly a foot across, and some cultivars have burgundy foliage that provides a pretty backdrop for the showy flowers. 

Dahlia plants are hardy in warm regions but can be saved year after year in colder areas by digging up their large, tuberous roots in the fall and replanting them in spring.

Where to Plant Dahlias

Dahlias need a sunny location with fertile, moist, well-draining soil with almost neutral pH (6.6 to 7). Because dahlias range from 1 foot for compact dahlias to more than 5 feet for taller varieties, always consider the plant's mature height. Also, take into consideration that dahlias won't survive the winter below zone 8 and need to be dug up in the fall. If you want to save them for next year, select a location with easy access.

How and When to Plant Dahlias

Dahlias are planted directly in the ground in late spring when the ground has warmed to at least 60°F, and all danger of frost has passed.

To get a head start on the growing season, start them indoors in early spring. Plant the bare-root tubers in well-draining potting soil about six weeks before the last frost. Place the pots in a warm, sunny window. Keep the soil evenly moist but not wet to avoid rot. Once the foliage emerges and the danger of frost has passed, transplant them into the ground.

Dig a 6- to 8-inch-deep hole for each tuber and add some compost or bonemeal. Place the tuber in the hole with the growing points (the “eye” that looks like a potato sprout) facing up. Loosely cover the tuber with 2 to 3 inches of soil. Don’t water it immediately; wait for the sprouts to poke through the soil. As the sprouts grow, gradually add more soil until the hole is filled.

The spacing depends on the variety. Smaller types are fine with 1 foot between them, but larger dahlias should be spaced at least 2 feet apart.

Most dahlias need staking. To prevent injury to the tubers, put the support in the ground before planting the dahlias.

Dahlia Care Tips

Light

Dahlias need full to partial sun. Full sun encourages upright plants that need less staking, but these plants will still flower in part shade. If planted in shadier areas, the foliage tends to look more green than burgundy on dark-leaved cultivars. Partial shade, especially during the afternoon hours, is a good idea in hot climates.

Soil and Water

The soil needs to be well-drained, rich, and moist, with a neutral pH between 6.6 and 7.

Right after planting, dahlias don’t need a lot of water. Overwatering in the early stages causes the tubers to rot. Once established, they need about 1 inch of water per week, more in hot weather. Always water them at the base, never from overhead. After heavy rain, large flowerheads might be filled with so much water that they bend over, so the plants might need gentle shaking to remove the water.

Temperature and Humidity

Dahlias are native to the mountains of southern Mexico and Central America, where the summers are warm but not excessively hot. They are not frost-hardy; below zone 8, they are grown as annuals. Dahlias do not have any particular humidity requirements or issues.

Fertilizer

Because you want your dahlias to bloom lushly over an extended period, regularly fertilize them with a bloom-boosting fertilizer low in nitrogen and high in phosphorus. For frequency, follow the product directions but stop fertilizing the plants towards the end of August so the tubers can prepare for dormancy.

Planting is a good time to incorporate an organic fertilizer 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, boosts bloom production, while the third number, potassium, helps root development. Any fertilizer recommended for vegetables is suitable for dahlias.

Pruning

To encourage a bushier growth habit, pinch off the top 3 to 4 inches of the center branch when the plants are about 1 foot tall. For fewer but larger flowers, also remove the two smaller side buds next to the central bud in each flower cluster. Deadheading the flowers extends the bloom season.

Potting and Repotting Dahlia

Dahlias, especially dwarf-size types, grow equally well in the ground or containers. Plant them in pots at least 16 inches in diameter and 12 inches deep and gradually add soil to the tubers as they start growing.

Make sure the container has large drain holes, and use a combination of well-draining potting mix and compost.

Like all potted plants, they will need more watering than dahlias in the landscape and more frequent fertilizer applications as the fertilizer washes out of the pot.

How to Stake Dahlias

Dahlia flowers are 2 to 10 inches wide, so some 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 that are 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.

Pests and Problems

Snails and slugs are often a problem for young plants. They are especially attracted to wet soil around them.

Insects that feed on dahlias include Japanese beetles, aphids, thrips, and earwigs. 

Dahlias are also prone to a range of fungal diseases, including gray mold on the tubers. In the worst case, you’ll have to restart with newly purchased tubers from a reliable source each year. Many pathogens survive in the soil over the winter, so to break the disease cycle, make sure that you don’t plant dahlias in the same location for at least three years.

How to Propagate Dahlias

Gardeners can propagate dahlias through stem cuttings, division, or seed. Both stem cuttings and divisions produce plants identical to the parent. Those grown from seed harvested from a dahlia are not identical to the parent.

Stem cuttings: In spring to early summer, cut 4- to 6-inch-long shoots with at least three sets of leaves from healthy stems. Leave two sets of leaves at the top of the cutting and remove the others. If the remaining leaves are longer than 2 inches, trim them to half their size. Fill 4-inch pots with moist sterile potting medium and create a hole in the center with a pencil-sized object. Dip the end of the cutting into rooting hormone and put it in the pot, pressing the planting medium around the stem. Place the pots in a warm place under a grow light where they receive at least 14 hours of light daily. Mist them occasionally until you see new growth.

Alternatively, take cuttings from tubers as they grow in the garden. As shoots appear above ground, cut them at the base and handle them as stem cuttings. Leave the tuber in place to produce additional growth.

Division: Divide dahlia tubers at planting time by cutting them into several pieces, each containing a piece of the main stem and an eye. It is easier to do this if you wait until the eyes sprout in storage. Place each division in a small pot with moist potting soil or sterile potting medium and keep it in a warm place until new growth appears.

Seed: Sow dahlia seeds indoors six to eight weeks before the last frost date in spring. Because they have a low germination rate, sandwich the seeds between two wet paper towels. Place the paper towels with seeds in a plastic bag and put them away somewhere warm for three to five days; then, check daily to see if they have started germinating. Carefully place any germinated seeds in a seed tray with seed-starting mix and cover them lightly with a dusting of the planting medium. Put the seed tray under grow lights. The seeds must be kept warm.

Continue to check the paper towels each day to see if more seeds have germinated. They don't all germinate at the same time. After a couple of weeks, discard any remaining ungerminated seeds and the paper towels. When the seedlings are large enough, transplant them into individual pots. Wait until after the weather warms in spring to move them outside, hardening them off first.

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 encourages the plant to produce more flowers. Be sure to deadhead any spent blooms, too.

Cutting Dahlias

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 open or nearly open flowers because the buds will not open after they're cut. You should cut as much length as you need for your bouquet but try to cut just above a set of leaf nodes and side buds. New shoots will grow from those nodes.

Conditioning and Arranging Dahlias

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. Leave the stems in the water for at least one hour. This hot-water treatment conditions the stems so the blooms last four to six days.

Next, strip off all the 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.

Types of Dahlia

Dahlias are classified into 14 groups based on blossom type. Here are some popular varieties.

'Arabian Night' Dahlia

'Arabian Night' offers deep maroon, almost black, blooms that open several to a stem and grow 3 feet tall.

'Bishop of Llandaff' Dahlia

This variety bears dark, fiery-red blooms shaped like small peonies that glow against deep chocolate foliage. This prize-winning dahlia grows 4 feet tall.

'Radar' Dahlia

Dahlia 'Radar' is a large, informal decorative-type that features deep plum-purple petals tipped in white. It grows 5 feet tall.

'Chinese Lantern' Dahlia

Dahlia 'Chinese Lantern' bears huge, bittersweet orange blooms that appear abundantly on branching stems from midsummer to fall. It grows 3 to 4 feet tall.

'Jessica' Dahlia

'Jessica' is a cactus-type dahlia that unfurls butter-yellow petals tipped in flame red. It grows 5 feet tall.

'Envy' Dahlia

Dahlia 'Envy' offers large, deep red blooms. It grows 5 feet tall.

'Duet' Dahlia

This type of dahlia features medium-sized red blooms tipped in white. It grows 3 feet tall.

'Pam Howden' Dahlia

Dahlia 'Pam Howden' is an abundantly blooming variety that features 2- to 4-inch-wide water-lily style flowers in an orange-yellow-coral blend. The plant grows 4 feet tall.

'Penn's Gift' Dahlia

'Penn's Gift' is known for its large pink flowers that may reach more than 1 foot across. It grows 5 feet tall.

Star Gazer Series Dahlia

Dahlia Star Gazer Series is a dwarf, cactus-flowered dahlia that produces spiky blooms in nine colors, including golds, yellows, deep reds, fuchsia, lavender, and bicolors with white. The multibranching plants grow 16 inches tall.

'Victory Dwarf' Dahlia

Dahlia 'Victory Dwarf' is a small, single-flowered variety that produces gemlike blooms in red, orange, yellow, and white. It grows to 8 inches tall.

'Sharon Ann' Dahlia

Dahlia 'Sharon Ann' is a semicactus-type dahlia with spiky light lavender petals unfolding from a creamy white center. It grows 5 feet tall.

'White Fawn' Dahlia

'White Fawn' offers pristine white blooms up to 4 inches wide on a plant that grows 4 feet tall.

'SB's Sunny' Dahlia

Dahlia 'SB's Sunny' is an award-winning variety that features layers of lemon yellow petals tightly clustered on a round, pompon flower. It grows 4 feet tall.

'Suffolk Punch' Dahlia

This type offers cherry-red flowers with an iridescent pink overtone bloom on dark stems. It grows 4 feet tall.

'Survivor' Dahlia

Dahlia 'Survivor' is a large decorative type with deep rose-pink blooms that reaches 12 inches across. It grows 5 feet tall.