Planting, Growing, and Caring for Dazzling 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
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.
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!
Planting
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 dahlia plant tubers indoors in containers a month ahead to get a jump on the season. Medium- to dwarf-size dahlias will do well in containers.
Where to Grow Dahlias
Dahlias thrive in 6 to 8 hours of direct sun, especially morning sunlight, and they benefit from protection from wind. Be sure to consider their mature size when planting, as some varieties can grow quite tall and wide. For optimal growth, dahlias prefer rich, well-draining soil with a pH between 6.0 and 7.5.
Preparing your soil before planting is key: if you have heavy clay soil, amend it with plenty of aged manure, compost, or peat moss to improve both drainage and aeration. Loosen the soil to a depth of at least 12 inches, removing any rocks or debris, so the tubers can expand easily. A well-prepared bed sets your dahlias up for strong root development and vibrant blooms.
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.
- Dahlias begin blooming about 8 weeks after planting.
Staking Dahlias
Staking dahlias (especially tall varieties with large, heavy blooms) is important for upright and healthy plants. Without support, their long stems can bend or break under the weight of the flowers or from wind and rain. Use sturdy 5- to 6-foot garden stakes, placing them around the plant shortly after planting to avoid damaging tubers later. As the dahlias grow, gently tie the stems to the stakes using soft garden twine, yarn, or plant ties. Secure them every foot or so up the stem.
Regular staking keeps your dahlias looking tidy, upright, and blooming beautifully all season long.
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 dahlia care:
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.
Photo: Terrywood72
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. These are beautiful as cut flowers.
- ‘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. These are great for containers and borders, and are prolific bloomers.
- ‘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. This is one of our favorite cutting varieties!
- ‘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.
Pests/Diseases
Diseases:
- Botrytis blight
- Southern blight
- Crown gall
- Powdery mildew
- Smut
- Virus
- Wilt
Pests:
- Aphids
- Caterpillars
- Earwigs
- Nematodes
- Slugs and snails
- Thrips
- Spider mites
Photo: Terrywood72
FAQ
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.
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.
Can you grow dahlias in pots?
Yes, you absolutely can (and we vote that you should!). Dahlias are simply dazzling in containers; just make sure that you choose a large enough pot to support their size at maturity and use a well-aerated potting mix.
Do deer eat dahlias? Are dahlias deer resistant?
A deer will eat anything if they are hungry enough, but fortunately, dahlias are not a deer’s favorite snack. Generally speaking, deer tend to avoid dahlias if there is enough other foliage to eat. Check out some of our favorite deer-resistant plants.
When do dahlias bloom?
One of the best qualities of dahlias is how, once they start blooming, they just don’t stop! Many varieties of dahlias bloom 90-100 days after planting; in many parts of the country, this means that June and July kick off the dahlia season, with August and September being the peak months. The flowers will continue to bloom until a hard frost or until the days become too short to satisfy their light requirements (typically around October).
Can you grow dahlias from seed?
While dahlias are typically grown from tubers, you can certainly grow them from seed. The only thing to know is that if you collect seeds from a dahlia you grew, it will not grow true to what you had in the garden. Only tubers will stay true to type. Growing dahlias from seed is how new varieties have been created.
If growing from seed, you will want to check the last spring frost date for your growing location and plant the seeds indoors 4 to 6 weeks before that date. Once the threat of frost has passed, you can start by slowly introducing them to outdoor conditions (hardening off) before planting in your garden or in a container.
Catherine Boeckmann
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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.
my dahlias did spectacularly well in a large pot from late spring until mid august, I did not stake them. now they have fallen over. how far back can I prune them. also the tuber is about half above ground. should I bury it?
Foliage should be cut back to 2 to 4 inches above ground and lifting and separating should be completed in early fall. Don’t bury it if you are going to lift to overwinter it later in season.
I live in so ind zone 6. first frost may be as late as thanksgiving! or early as mid october. also. I watered my plant heavily the nite before it fell over
I have replanted my tubers each year and all the plants that have bloomed are yellow blossoms even though many were of a different color...why have they all turned to a yellow blossom??
I have had my Dahlias in the ground for some time in Zone 6. All of the leaves have been deep green until this week. A few of the plants have begun to have very light green almost yellow on some of the leaves. What should I do, Fertilize again ??What with? an you help me.
??
what do i do
