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!
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!
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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.
How to Plant Dahlia Tubers
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
Fertilizing
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.
Dahlia Growing Tips
- 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!
Pests and Problems
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.
Types
There are about 60,000 named varieties and 18 official flower forms, including cactus, peony, anemone, stellar, collarette, and waterlily. Learn more about how to pick out the right dahlia for you.
We recommend checking out the National Dahlia Society for more information about specific varieties.
More Like This
Hi Molly, it sounds to us like it's time to get some new plants; dahlias sprout after 2 to 4 weeks and it's been two months since Easter. Best of luck, —The Editors
Hi Barbara,
You could try soap or Neem oil at this stage; here is Almanac.com's complete guide to dealing with scale.
—The Editors
Hi Eva,
There could be a few reasons why your dahlia buds are not opening. The first thing would be to examine your watering practices. Waterlogged roots from excessive water can affect the buds' ability to open. Also, if your dahlia was planted in poorly draining potting mix or a container that holds water it can lead to too much water that will hinder your buds from turning into flowers. A lack of water can also be an issue, as container planted dahlias need consistent watering because the potting mix dries out a lot faster than those planted in the ground.
If your watering schedule is consistent, it could be an underlying pest issue. If the stems and leaves appear normal but buds are not opening, check them for small holes to determine if thrips or earwigs have punctured or chewed them. Buds that have been repeatedly affected by these pests might not open properly.
Another issue could be excess fertilization in the form of too much nitrogen. If the plant is overfertilized, it will grow luscious foliage at the expense of flowers.
Hope this helps!
Hi, Subia. We are sorry to hear about your dahlias. They can be fickle plants in hot climates, as they prefer warm days and cooler nights. Here are a few things to try to revive your plants: Add organic matter to your containers. Keep watering (do not soak), and try adding some mulch on top to cool them down. Also, if your dahlias are in full sun, move them so that they get some shade. If all else fails, we highly recommend looking into getting a heat-tolerant variety. They may perform better in your climate.
Hi Dollie,
Dahlias certainly are beautiful. You definitely want to wait until it has finished blooming, but it is best to wait until the first frost has hit or the leaves have turned brown. At that point, you could transplant your tuber to a new container with fresh potting mix and store indoors in a cool, dark room for the winter. But it would probably make more sense to simply remove the tuber from the current container and store it as outlined above for the winter before then putting the tuber in a new container in the spring. That way you don't have to lug the new, larger container (which will be heavier) in this fall and out again next spring.
Good luck!
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