Planting, Growing, and Caring for Dahlias from Spring to Fall
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If flowers had a runway, dahlias would steal the show. Whether you’re aiming for pint-sized pom-poms or dinner-plate divas, these late-season stars bloom from midsummer straight through fall. In this cheerful guide, we’ll walk you through how to grow dahlias, from burying those funny-looking tubers in spring to snipping the last bloom before frost. Grab your gardening gloves—it’s dahlia time!
About Dahlia Flowers
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. Dahlias grow in a wide range of beautiful colors, including white, yellow, orange, pink, dark pink, red, dark red, lavender, purple, black, light blend, bronze, flame, dark blend, variegated, and bicolor!
Dahlia is a genus of tuberous plants that are members of the Asteraceae family. The tubers are planted in the ground in late spring (around the month of May) 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 or Annuals?
Dahlias are tender perennials in their native warm climate of Mexico. In the United States, they are considered perennials in hardiness Zones 8 and higher. See the USDA hardiness zone page.
However, in colder regions (Zones 7 and lower), dahlias are treated as annuals. That said, some gardeners have had luck keeping the dahlias in the ground in Zones 6 and 7.
Luckily, cold-weather gardeners can also just dig up the tubers after the first fall frost and store them in the garage until spring. Learn how to dig up dahlias in the guide below.
Planting
Where to Grow Dahlias
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 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 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 an excellent 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.
Start by digging a 6- to 8-inch deep hole to plant the tubers. 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:
Growing
Watering Dahlias
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) fill up with water or take a beating from the wind.
Dahlia Growing Tips
- 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 its energy into fewer but considerably larger flowers.
- Bedding dahlias need no staking or disbudding. Simply pinch 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!
Types
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 hand-size pink flowers in fall; 4 to 6 feet tall
We recommend checking out the National Dahlia Society for more information about specific varieties.
Catherine Boeckmann
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The general consensus is not to break off the shoots and plant the dahlia tuber as you would normally. If there is any rot, cut it off, and be aware that if the tubers are dried out, they may not thrive or grow. A reader wrote in to endorse the idea of leaving the tubers as is: “I never break them off [when] they grow new shoots, [and] never have a problem with them growing.”
Hi, I have 2 pots of Dahlia, one is flowering nice but the other is just growing bushy with tiny buds which do not open. How do I treat it?
Thank you from Ghana.
I have potted plants that look healthy and have buds but do not open.
What if some tubers fall off when pulling out? Are they still good?
If your dahlia tubers fall apart when being lifted out of the ground, then they are rotten and should be disposed of. If it’s just the foliage that detaches from the tubers, the tubers themselves are probably just fine; you’ll have to dig them up and have a closer look. If they are squishy and fall apart easily, then they are no good. In the fall, especially after a frost, the foliage dies off naturally, which is when it easily detaches from the tuber.
I live in the Seattle area, did not replant my very dark purple dahlia for 5 yrs, this year the plant bloom in a yellow and orange color, WHY?
Thank you, Renee
I live in England and have experienced this with blue hydrangeas that turned pink. I researched and learnt that at transplanting, the acidity of the soil has a bearing on the flower colour. Solution is to buy erocutious compost. I use this for camelias as well
Some cultivars of dahlias (and other common-grown flowers) are not genetically “stable,” meaning the flowers they send up may not always be the same color or shape. Your original purple dahlia was likely a hybrid of several other dahlias, and it just so happens that another color showed up this time.
For the last two years I have grown the most abundant and beautiful dahlia. They had very large blooms. However after I dug them up in the fall and stored them over winter they did not grow. This year I bought new tubers and they grew tall but the flowers did not fully bloom they were undeveloped and looked sick. It was very dry here so I watered them but they were slow to come up and the blooms would not develop
There are a couple things that could have resulted in weak dahlias:
1. The tubers themselves could have come from a bad or diseased source.
2. There aren’t enough nutrients in the soil. Did you add any fertilizer to the soil before planting? Dahlias are heavy feeders, so having two seasons of dahlias grow in the same spot without any extra fertilizer could have simply depleted the soil’s resources. See our advice, above, about fertilizing dahlias.
