How to Plant, Grow, and Care for Dahlias
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.
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 12x12 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.
Check out our video to learn more about growing dahlias in your garden:
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!
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
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I live near Portland, OR. Do I need to lift my dalias?
Check your hardiness zone. If you are in 7 or above, you should be alright leaving them in the ground.
Six years ago, I bought a package of seed dahlias and planted them in an area in front of our house which is somewhat protected from the weather. The first year they bloomed and were about six inches high. Since then, they have spread over the area and bloomed on their own producing beautiful variety of colors. I have never dug them up after blooming but left them alone. The plants are 12 inches to 3 feet high. I didn't think dahlias spreads. What type of dahlias are these?
We’ve only grown dahlias from tubers, is is tradition. However, it is true that that the dahlia flower will produce both seeds and tubers when grown so you could propagate from either. It doesn’t matter which type of dahlia because the tubers will always and consistently produce copies of their “mother” dahlia, but the seeds will not. According to the American Dahlia Society, dahlia seeds will produce varieties different from the parent plants, so propagation from seeds is used primarily to develop new cultivars. Think of it as the dahlia “mother” reproducing with any plant “father” whose pollen an insect carried to the mother. Therefore, it’s not surprising you had a diverse variety of children, since they had the same mothers but different dads. The seeds you plant will never grow true to type but that’s part of the adventure.
I’m in California—how many years can dahlias stay in the ground before you need to divide? Three years?
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