Gardening Guides
Planting Guide: How to Grow Dahlias
Plant these quick-growing bloomers in spring for a dazzling flower display from midsummer to fall
Easy to grow and with a rainbow of colors to choose from, dahlias are some of the most widely grown garden flowers. If you’ve never grown them before, you’re in for a treat. Starting from humble, potato-like tubers stuck into the ground in spring, dahlias grow — as if by magic — into lush plants covered in luxurious flowers within a few months.
Check out our step-by-step planting guide below, including tips for how to get the most flowers per plant in a home garden and how to extend your flowering season up until the first frost in fall.
Check out our step-by-step planting guide below, including tips for how to get the most flowers per plant in a home garden and how to extend your flowering season up until the first frost in fall.
Originally native to Central America, dahlias are tender, warm-season perennials grown from tubers. The flowers are classified by form and range from pompom to waterlily forms. Bedding and bush dahlias are most commonly available and widely grown, and the instructions below refer to these types. Less common tree dahlias (Dahlia imperialis) can reach up to 20 feet tall and require staking.
Dahlia ‘All Triumph’
How to Plant Dahlias
1. Select your planting area. Dahlias grow best in full sun in most regions, but appreciate light shade in hot inland areas. Tubers can rot if the soil gets too soggy, so choose an area with quick-draining soil or plan to amend the bed well with compost.
2. Prep the soil. Remove any weeds from the bed and turn over the soil with a shovel, breaking up clods. Add a generous heap of well-decomposed compost (enough to cover the bed with 2 to 4 inches) and turn over the soil. If your native garden soil is slow-draining clay, add a 2- to 4-inch layer of compost and turn over the soil once again. Rake the bed smooth.
3. Dig a planting hole. Using a hand trowel, dig a hole 4 to 6 inches deep.
How to Plant Dahlias
1. Select your planting area. Dahlias grow best in full sun in most regions, but appreciate light shade in hot inland areas. Tubers can rot if the soil gets too soggy, so choose an area with quick-draining soil or plan to amend the bed well with compost.
2. Prep the soil. Remove any weeds from the bed and turn over the soil with a shovel, breaking up clods. Add a generous heap of well-decomposed compost (enough to cover the bed with 2 to 4 inches) and turn over the soil. If your native garden soil is slow-draining clay, add a 2- to 4-inch layer of compost and turn over the soil once again. Rake the bed smooth.
3. Dig a planting hole. Using a hand trowel, dig a hole 4 to 6 inches deep.
4. Place the tuber in the hole, growth bud facing up. Plant one tuber per hole, keeping the growing bud pointing up and roots pointing down, laying the tuber horizontally. For tubers that do not have an obvious growth bud (a little green or white shoot), look for a preshoot “growth eye” — which can look like a small dimple in the tuber.
Optional: Add a sprinkle of bone meal — available at most nurseries — at the bottom of each hole before planting the tuber.
5. Stake before covering the tuber. For dahlia varieties that reach over 4 feet tall, drive a tall stake into the ground close to the tuber to support the plant as it grows.
6. Cover with soil. Backfill the hole with soil, covering the tuber and bottom 4 to 6 inches of the stake, if using one. Wait to water until the first green shoots emerge above soil, to avoid rotting.
Spacing: Allow 12 to 18 inches between plants for most varieties (those that reach 3 to 5 feet tall). Smaller bedding dahlias can be spaced closer together (9 to 12 inches), and larger dahlias (5 or more feet tall) can take a few feet between them.
Optional: Add a sprinkle of bone meal — available at most nurseries — at the bottom of each hole before planting the tuber.
5. Stake before covering the tuber. For dahlia varieties that reach over 4 feet tall, drive a tall stake into the ground close to the tuber to support the plant as it grows.
6. Cover with soil. Backfill the hole with soil, covering the tuber and bottom 4 to 6 inches of the stake, if using one. Wait to water until the first green shoots emerge above soil, to avoid rotting.
Spacing: Allow 12 to 18 inches between plants for most varieties (those that reach 3 to 5 feet tall). Smaller bedding dahlias can be spaced closer together (9 to 12 inches), and larger dahlias (5 or more feet tall) can take a few feet between them.
Plant Care Throughout the Season
Water. Once the first shoots emerge above the soil, keep the soil consistently moist but not soggy throughout the growing season. It’s best to set up a soaker hose or drip irrigation system to be able to easily water plants without getting the leaves wet, which can lead to mildew.
Pinching. Once young dahlia plants reach about a foot tall, pinch back the terminal bud (main center shoot) to encourage lateral branching. It seems counterintuitive, and even a bit brutal, to pinch back a young shoot, but — trust me on this one — the technique can as much as double the overall number of flowers per plant. Plus, pinched young plants form bushier mature plants, which can be easier to manage in garden beds. For smaller varieties of dahlias (under 4 feet), one pinching is enough to increase flowers and branching. For dahlia varieties over 4 feet tall, pinch a second time when the plant reaches 18 inches tall.
Water. Once the first shoots emerge above the soil, keep the soil consistently moist but not soggy throughout the growing season. It’s best to set up a soaker hose or drip irrigation system to be able to easily water plants without getting the leaves wet, which can lead to mildew.
Pinching. Once young dahlia plants reach about a foot tall, pinch back the terminal bud (main center shoot) to encourage lateral branching. It seems counterintuitive, and even a bit brutal, to pinch back a young shoot, but — trust me on this one — the technique can as much as double the overall number of flowers per plant. Plus, pinched young plants form bushier mature plants, which can be easier to manage in garden beds. For smaller varieties of dahlias (under 4 feet), one pinching is enough to increase flowers and branching. For dahlia varieties over 4 feet tall, pinch a second time when the plant reaches 18 inches tall.
Midseason staking. Dahlias have fragile, hollow stems that can easily snap with the weight of flowers. If you staked a taller variety at planting time, tie the central stems of the plant to the stake as it grows to help support the weight of the plant. For smaller dahlias (or extra support for tall, bushy varieties), arrange three or four stakes around a plant and encircle the stakes with twine to support lateral shoots.
Cutting Flowers for Bouquets
Select blooms to cut that are just starting to open or are fully open but not looking tired yet — before the edges of their petals start to brown. Unlike many other flowers, dahlias do not continue to open very much once cut from the plant.
Put cut flowers into water immediately and do not overfill the vase with water, to help preserve the fragile, hollow stems. Dahlias last about a week in a vase.
Select blooms to cut that are just starting to open or are fully open but not looking tired yet — before the edges of their petals start to brown. Unlike many other flowers, dahlias do not continue to open very much once cut from the plant.
Put cut flowers into water immediately and do not overfill the vase with water, to help preserve the fragile, hollow stems. Dahlias last about a week in a vase.
How to Extend Blooms
Harvest dahlias frequently at the height of bloom season to encourage new flowers to keep forming on the plant. Deadhead flowers past their prime. With consistent picking and good health, the plants will keep producing flowers until the first frost in fall.
Harvest dahlias frequently at the height of bloom season to encourage new flowers to keep forming on the plant. Deadhead flowers past their prime. With consistent picking and good health, the plants will keep producing flowers until the first frost in fall.
Pests and Diseases
Snails and slugs. Shoots on young plants can be damaged from slugs and snails. Use bait (like pet-safe, organic Sluggo Plus, available from garden supply stores) around the bases of plants to prevent damage.
Earwigs. These bugs can be a problem if they burrow into buds and leave holes in the flowers. Control earwigs with bait (Sluggo Plus works), or knock them off buds and flowers, holding a bowl of water underneath.
Powdery mildew. Mildew can be a problem in cool-summer climates and coastal areas, often showing up as dusty white spots on leaves later in the season. While you can use a fungicide spray to counteract mildew, there aren’t organic options commonly available, so it’s not advised.
Decrease the chance of plants’ getting mildew by avoiding getting water on leaves — water plants at the base; don’t spray from overhead. Don’t worry too much if your plants have mildew, however; the powdery fungus targets primarily the leaves and stems, leaving flowers largely unaffected.
Snails and slugs. Shoots on young plants can be damaged from slugs and snails. Use bait (like pet-safe, organic Sluggo Plus, available from garden supply stores) around the bases of plants to prevent damage.
Earwigs. These bugs can be a problem if they burrow into buds and leave holes in the flowers. Control earwigs with bait (Sluggo Plus works), or knock them off buds and flowers, holding a bowl of water underneath.
Powdery mildew. Mildew can be a problem in cool-summer climates and coastal areas, often showing up as dusty white spots on leaves later in the season. While you can use a fungicide spray to counteract mildew, there aren’t organic options commonly available, so it’s not advised.
Decrease the chance of plants’ getting mildew by avoiding getting water on leaves — water plants at the base; don’t spray from overhead. Don’t worry too much if your plants have mildew, however; the powdery fungus targets primarily the leaves and stems, leaving flowers largely unaffected.
Show us your dahlias: What’s your favorite variety to grow in a home garden? Post your photos in the Comments.
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Common name: Dahlia
Where it will grow: In USDA zones 8 to 10 (find your zone) dahlias can be grown as perennials, leaving tubers in the soil in winter; for Zone 7 and colder, lift bulbs from the ground to overwinter
Water requirement: Moderate
Light requirement: Full sun to light shade in the hottest regions
Mature size: 1 foot to 4 feet wide and 1 foot to 7 or more feet tall, depending on variety
Bloom time: Midsummer to the first frost in fall
When to plant: After the last frost in spring (usually March or April), until early June