How to Grow and Care for Dahlias

Dahlias deliver some of the biggest, most dramatic blooms in the garden, flowering non-stop from midsummer until the first frost. They grow from tubers planted in spring, and in cold climates those tubers are lifted and stored over winter so you can replant them each year. Here’s how to plant, grow, feed and overwinter dahlias.

When to plant dahlias

Plant dahlia tubers in spring after all danger of frost has passed and the soil has warmed to about 60°F (15°C) — dahlias are frost-tender and won’t tolerate cold, wet ground. In most regions that’s mid-to-late spring. To get a head start, you can pot tubers up indoors a few weeks earlier and move them outside once it’s warm.

How to plant and grow dahlias

Choose a sunny, sheltered spot with rich, well-drained soil. Plant tubers on their side about 4 to 6 inches deep with the growing “eye” facing up, spacing them 1 to 2 feet apart depending on the variety. For tall types, push a stake in at planting time so you don’t spear the tuber later.

Hold off on heavy watering until you see shoots above ground — wet soil can rot a dormant tuber. Once they’re growing, water deeply two or three times a week. When plants reach about 12 inches tall, pinch out the central growing tip to encourage bushier plants and more flowers.

• Plant tubers 4–6 inches deep, eye up
• Stake tall varieties at planting time
• Don’t overwater until shoots appear
• Pinch at 12 inches for more blooms

Dahlia care and feeding

Dahlias are hungry for blooms, not leaves — feed with a low-nitrogen, higher-potassium fertilizer (the kind used for tomatoes works well) every few weeks through summer. Too much nitrogen gives you lush foliage and few flowers.

Deadhead spent blooms regularly to keep new ones coming; the trick is telling old buds (pointed) from spent flowers (rounded, soft) and removing the latter. Keep plants well watered and mulched through the hottest part of summer.

How to lift and store dahlia tubers

In zones 8 and warmer, dahlias can often stay in the ground over winter with a thick mulch. In colder areas, lift and store the tubers so they survive to next year.

1. After the first frost blackens the foliage, cut the stems back to a few inches.
2. Carefully dig up the tuber clumps with a fork, avoiding damage.
3. Brush off soil and let them cure in a dry, airy spot for a few days.
4. Pack the tubers in a box of dry peat, vermiculite or sawdust.
5. Store somewhere cool, dark and frost-free (around 40–50°F) over winter, and replant in spring.

Common dahlia problems

If dahlias grow lots of leaves but few flowers, the culprit is usually too much nitrogen or not enough sun. Slugs and snails love young dahlia shoots, and earwigs chew the petals — deal with them early in the season. Powdery mildew can appear late in summer; space plants for airflow and water at the base to reduce it.

Types of dahlias

Dahlias are classified by flower form and size, from tiny pompons to plate-sized giants. Dinnerplate dahlias produce enormous blooms up to 10 inches across on tall plants and always need staking. Ball and pompon dahlias have neat, rounded, geometric flowers that are excellent for cutting. Cactus and semi-cactus types have spiky, quilled petals, while decorative and waterlily forms give the classic full, layered look. Choosing a range of forms and heights gives a long, varied display.

• Dinnerplate: huge blooms, tall plants, must be staked
• Ball & pompon: neat rounded flowers, great for cutting
• Cactus & semi-cactus: spiky, quilled petals
• Decorative & waterlily: full, classic layered blooms

Growing dahlias in containers

Compact and dwarf dahlias grow well in pots, making them a good choice for patios and small gardens. Use a container at least 12 to 16 inches wide with good drainage, plant one tuber per pot in a quality potting mix, and stake taller varieties. Container dahlias dry out faster than those in the ground, so check the moisture regularly and feed with a low-nitrogen fertilizer through summer. In cold climates, you can move the whole pot somewhere frost-free or lift and store the tuber as usual.

Quick dahlia growing tips

Dahlias flower non-stop from midsummer to frost when you cover the essentials:

• Plant tubers after the last frost, 4–6 inches deep with the eye up
• Give them full sun and stake tall varieties at planting time
• Hold off heavy watering until shoots appear to avoid rot
• Pinch the tips at about 12 inches for bushier, more floriferous plants
• Feed a low-nitrogen, high-potassium fertilizer for more blooms
• Deadhead the rounded, spent flowers regularly
• In cold zones, lift and store the tubers over winter

Feed for flowers, not leaves, and deadhead often for months of color.

Dahlia growing FAQs

When should I plant dahlias?

Plant dahlia tubers in spring after the last frost, once the soil has warmed to about 60°F. Dahlias are frost-tender, so cold, wet soil will rot the tubers. You can start them indoors in pots a few weeks early and move them out after frost for earlier blooms.

How do you grow dahlias?

Plant tubers 4–6 inches deep with the eye up in a sunny, well-drained spot, spacing them 1–2 feet apart and staking tall types. Hold off heavy watering until shoots appear, then water deeply, pinch the tips at about 12 inches, feed a low-nitrogen fertilizer, and deadhead for constant blooms.

How do you store dahlia tubers over winter?

After the first frost blackens the foliage, cut the stems back, dig up the tubers, and let them cure for a few days. Pack them in dry peat, vermiculite or sawdust and store somewhere cool, dark and frost-free (around 40–50°F). Replant in spring after the last frost.

Do you have to dig up dahlias every year?

Only in cold climates. In zones 8 and warmer, dahlias can overwinter in the ground under a thick mulch. In colder zones they’re frost-tender, so you lift and store the tubers indoors over winter, then replant them in spring.

Why are my dahlias not blooming?

The most common reasons are too much nitrogen fertilizer, which produces leaves instead of flowers, and too little sun — dahlias need six to eight hours a day. Feeding a low-nitrogen, high-potassium fertilizer and deadheading regularly encourages continuous blooms.

Should you pinch out dahlias?

Yes. When plants reach about 12 inches tall, pinch out the central growing tip just above a set of leaves. This encourages side shoots, producing a bushier plant with many more flowers than an unpinched dahlia.

See the dahlia flower profile, dahlia meaning guide, and the national flower of Mexico.