Dahlia Planting, Growing, and Care Instructions

Dahlias are breathtakingly gorgeous late-season flowers that bloom from midsummer through fall in a rainbow of color. Dahlias are perennials in Zones 8 and higher; in cold climates, they need to be dug up and stored until spring. Learn how to plant dahlia tubers and great tips on how to grow dahlias!

About Dahlia Flowers

Dahlia is a genus of tuberous plants that are members of the Asteraceae family, which also includes the sunflower, daisy, chrysanthemum, zinnia, and, of course, aster.

Picking a favorite dahlia is like going through a button box. The flowers can range in size from petite 2-inch lollipop-style pompoms to giant 15-inch “dinner plates.” Most varieties grow 4 to 5 feet tall. Plus, dahlias grow in a wide range of beautiful colors, including white, yellow, orange, pink, dark pink, red, dark red, lavender, purple and black, light blend, bronze, flame, dark blend, variegated and bicolor!

Tubers are planted in the ground in late spring and generally flower from July to the first autumn frosts. Dahlias are perfect for a border garden and make lovely cut flowers. Growing vegetables? Put a row of dahlias on the border, where they will not shade your edibles.

Are Dahlias Perennials?

It depends. Dahlias are considered a tender perennial in colder regions of North America. They are reliably winter hardy in hardiness zones 8 and higher. In colder zones, dahlias can either be treated as annuals or the tubers can be dug up after the first frost and stored indoors for winter and replanted in spring. For gardeners in zones 6 and 7, it can vary and some have luck keeping tubers in the ground. (See what hardiness zone you’re in!)

Dahlias love moist, moderate climates and full sun. Though not well suited to extremely hot climates (such as southern Florida or Texas), dahlias brighten up any sunny garden with a growing season that’s at least 120 days long.

PLANTING

Dahlias thrive in 6 to 8 hours of direct sun, especially morning sunlight, and they benefit from protection from wind. Consider their size at maturity when planting. They grow best in rich, well-draining soil with a pH level of 6.0 to 7.5. Amend heavy clay soil with aged manure or compost to lighten and loosen the soil texture for better drainage.

When to Plant Dahlias

Dahlias will not tolerate cold soil. Plant when the soil reaches 60ºF (15°C) and any danger of frost has passed.
Planting dahlias a few days after tomatoes are planted in the ground is a good rule of thumb.
Some gardeners start tubers indoors in containers a month ahead to get a jump on the season. Medium to dwarf-size dahlias will do well in containers.

How to Plant Dahlias

Avoid planting dahlia tubers that appear wrinkled or rotten. Pink “eyes” (buds) or a little bit of green growth are good signs.

Plant large dahlias and those grown solely as cut flowers in a dedicated plot where they will be free from competition from other plants. Set tubers in rows spaced 3 feet apart. If you plant dahlias about 1 foot apart, they make a nice flowering hedge and will support each other.
Plant medium- to low-height dahlias, usually in the 3-foot tall range, among other summer flowers. Set them 2 feet apart.
Plant the smallest bedding dahlias, grown from seed, 9 to 12 inches apart.

To plant the tubers, start by digging a 6- to 8-inch deep hole. It also helps to mix some compost and a handful of bonemeal into the planting hole. Otherwise, do not fertilize at planting.

Set a tuber into the hole with the growing points, or “eyes,” facing up.
Do not break or cut individual dahlia tubers (as you would with potatoes).
Cover the tuber with 2 to 3 inches of soil. (Some say 1 inch is adequate.)
As the stem sprouts, fill in with soil until it is at ground level.
Do not water the tubers right after planting. This encourages rot. Wait until the sprouts have appeared above the soil, then water.
Do not spread mulch. Dahlias prefer sun on their roots, plus mulch harbors slugs.
Tall, large-flower cultivars require support. Place 5- to 6-foot stakes around plants and tie stems to them as the plants grow.
Dahlias begin blooming about 8 weeks after planting.

Growing Dahlias in Containers

Medium- to dwarf-size dahlias do well in containers that have drainage and are big enough to support the plant at maturity. Generally, a 12×12 inch container will suffice.

Use a soilless mix and co-polymer moisture-retaining crystals, per the package’s guidance.
Follow the depth requirements.
Cover the tuber with a few inches of soil-crystal mix.
Spray water on the tuber, if necessary, until growth starts.
Do not water if the soil is damp 1 inch below the surface.
Fertilize through summer as directed.
Add soil if the roots become exposed.

GROWING

When dahlias are established, water 2 or 3 times a week and more in hot, dry climates. Be prepared to tend to plants before or after rain, when open blooms (especially large ones) tend to fill up with water or take a beating from the wind.

After sprouting, dahlias benefit from a low-nitrogen, liquid fertilizer, such as 5-10-10 or 10-20-20. Fertilize every 3 to 4 weeks from sprouting in midsummer until early autumn. Do not over fertilize, especially with nitrogen, or you risk small or no blooms, weak tubers, or rot.
When plants are about 1 foot tall, pinch out 3 to 4 inches of the center branch to encourage bushier plants and increase stem count and stem length.
For large flowers, try disbudding: Remove the two smaller buds next to the central one in a flower cluster. The plant will put all of its energy into fewer but considerably larger flowers.
Bedding dahlias need no staking or disbudding. Simply pinch out the center shoot just above the third set of leaves to encourage bushiness.
For more blooms, deadhead as flowers fade; deadheading keeps the flowers blooming for months!

RECOMMENDED VARIETIES

There are about 60,000 named varieties and 18 official flower forms, including cactus, peony, anemone, stellar, collarette, and waterlily. Here are some popular choices:

‘Bishop of Llandaff’: small, scarlet, intense flowers; handsome, dark-burgundy foliage; 3 feet tall
‘Miss Rose Fletcher’: an elegant, spiky, pink cactus plant with 6-inch globes of long, quilled, shell-pink petals; 4 feet tall
‘Bonne Esperance’, aka ‘Good Hope’: dwarf variety that bears 1-1/2-inch, rosy-pink flowers all summer that are reminiscent of Victorian bedding dahlias; 1-foot tall
‘Kidd’s Climax’: the ultimate in irrational beauty with 10-inch “dinnerplate” flowers with hundreds of pink petals suffused with gold; 3-1/2 feet tall
‘Jersey’s Beauty’: 4- to 6-inch handsize pink flowers in fall; 4 to 6 feet tall

HARVESTING

The more you cut dahlias, the more they’ll bloom! For a bouquet, cut stems in the morning before the heat of the day and put them into a bucket of cool water. Remove stems’ bottom leaves and place the flowers into a vase of water. Place the vase in a cool spot and out of direct sun. Check the water daily. Vase life is about 7 days.

Dig Up and Storing Dahlia Tubers

Dahlias are hardy to Zone 8; in these more temperate regions, dahlias can simply be cut back and their tubers left in the ground through winter; cover with several inches of dry mulch. In Zones 7, some gardeners claim their tubers survive winter in the ground; other gardeners have had varied results. It all depends on the severity of winter; native to Mexico, dahlias won’t survive freezing temperatures. → Find your USDA Hardiness Zone here.

In Zones 8 and north, simply dig up (lift) and store tuberous roots in late fall; tubers can be expensive and this will save you the money that would otherwise go into buying new ones each year. See your fall frost dates

Dahlia foliage blackens with the first frost. Take it as a warning to begin digging up the tubers. Complete the task before a hard frost.
Cut off blackened foliage, leaving 2 to 4 inches of top growth.
Carefully dig around tubers with a pitchfork, garden fork, or shovel. Avoid damaging them.
Lift the clump and gently shake off the soil.
Cut off rotten tubers.
Leave clumps outside in the sun upside down to dry naturally for a few days.
Pack them in loose, fluffy material (e.g., vermiculite, dry sand).

Store in a well-ventilated, frost-free space: 40º to 45ºF is ideal, 35º to 50ºF is acceptable.
Check on the dahlia tubers occasionally over the winter. Remove any tubers that have started to rot before the decay spreads to healthy tubers.

Readying for Summer

In spring, separate healthy tubers from the parent clump and discard wrinkled or rotten ones. Plan to plant the survivors. Each tuber must have at least one “eye” or piece of the crown attached or it will not develop into a blooming plant. The eyes are little pink bumps at the base of the stem. → See our gardener’s article on how to unpack and divide your stored dahlia tubers!

If this all seems like too much bother or you do not have the right storage place, skip it all and treat dahlias as annuals, buying new tubers in the spring.

WIT AND WISDOM

The dahlia was named for Anders Dahl (Swedish botanist), 𝐛𝐨𝐫𝐧 on March 17, 1751.
In the 16th century, dahlias grew wild on the hillsides in parts of Mexico. There, they were “discovered” by the Spanish.
Both dahlia flowers and tubers are edible. The tubers taste like a cross between a potato and a radish.