Dahlia

A tuberous perennial producing spectacular blooms from midsummer to frost, with tubers stored over winter in cold climates. Plant tubers after the last frost in rich, well-drained soil and stake tall dinner-plate varieties early to support their heavy flower heads. Pinch the central growing tip when plants reach about a foot tall to encourage branching and more abundant blooms. Dig tubers after the first frost blackens the foliage, divide clumps, and store in peat moss in a cool, frost-free location.

Dahlia tubers should be planted four to six inches deep with the eye pointing upward, spaced eighteen to twenty-four inches apart for standard varieties and up to three feet for dinner-plate types. In short-season climates, start tubers indoors in pots four to six weeks before the last frost to get a head start on the growing season. Set pots in a warm location and water sparingly until green shoots appear. Transplant outdoors after all frost danger has passed and soil is warm. Dahlias can also be grown from seed, started indoors eight to ten weeks before the last frost, though seed-grown plants are variable.

The Season Plate

Your Dahlia Year

Composed for Zone 7 · typical seasons · frost passes Apr 2, returns Nov 1

Sow Dahlia Apr – May, pick Jul – Oct. Set your climate below and every date on this plate re-times itself.

Sowing window

Apr – May

re-timed to your frost dates

Plant out

after Apr 2

once frost risk has passed

First picking

around Jul 14

≈ 90 days from sowing · 20-40 cut per plant

Composed for —ColdTemperateMildWarmUse my locationUsed once to set your season · only the zone is kept

Week-by-week Dahlia reminders watering, feeding and pruning, timed to your dates

In the app

Frost alerts for your garden a warning before a cold night costs you the crop

In the app

Succession sowing dates so the picking never gaps mid-season

In the app

Keep my dates — free for 7 daysWe nudge you as each window opens · cancel anytime

Prepare a planting site in full sun with rich, well-drained soil amended with generous amounts of compost. Dahlia tubers should not be planted until the soil has warmed to at least 60 degrees Fahrenheit, typically two to four weeks after the last frost. Dig a hole six to eight inches deep, lay the tuber horizontally with the eye or growing point facing up, and cover with two to three inches of soil. Do not water until shoots emerge, as wet tubers are prone to rotting.

As plants grow, gradually fill in the remaining soil around the stems. Install stakes or support cages at planting time to avoid damaging tubers later. When the main stem has three to four sets of leaves, pinch out the center growing tip to encourage bushier growth and more flower stems. Remove the two smaller side buds that form below each terminal flower bud for larger, showier blooms.

Water deeply two to three times per week during active growth and flowering, and apply a layer of mulch to conserve moisture and keep roots cool. Feed every two to three weeks with a low-nitrogen, high-phosphorus fertilizer to promote flowering over foliage growth. After the first frost blackens the foliage, cut stems back to four inches, carefully dig tubers, and store in a cool, frost-free location for winter.

Dahlias pair well with other late-summer bloomers like zinnias, sunflowers, and marigolds for a continuous display of warm colors. Low-growing companion plants such as alyssum and lobelia shade dahlia roots and conserve soil moisture. Planting garlic and chives nearby helps deter aphids, which can transmit dahlia mosaic virus. The large blooms attract beneficial pollinators that also serve neighboring vegetable crops.

The Society Table

Marigold belongs beside it. Fennel doesn't.

Old growers' knowledge, checked against Dahlia's real companion table below — test any plant you're growing.

Grows well in the company of · 3

MarigoldZinniaSunflower

Keep apart · 1

Fennel

Plant Dahlia with good neighboursThe planner flags conflicts before they're in the ground

Dahlias demand rich, well-drained soil with a pH of 6.5 to 7.0. Heavy clay soils should be amended with compost and coarse sand to prevent tuber rot. Work a generous amount of aged compost into the planting bed before setting tubers. Use a fertilizer low in nitrogen and high in phosphorus and potassium, such as 5-10-10, applied every two to three weeks during the growing season. Too much nitrogen produces lush foliage with fewer, smaller flowers.

Ideal Temperature

Hardiness Zone Compatibility

Cut dahlia stems for arrangements in the early morning when flowers are about three-quarters open. Choose blooms where the outer petals are fully unfurled but the center is still tight. Cut stems long, placing them immediately into hot water (about 160 degrees Fahrenheit) for one hour to sear the stems and extend vase life. Deadhead spent flowers regularly by cutting back to a main branch to encourage continuous blooming until frost.

Storage & Preservation

Dahlia tubers must be dug and stored in cold climates where soil freezes. After the first frost kills the foliage, cut stems back and carefully lift clumps with a garden fork. Rinse soil from tubers and let them dry for a day in a sheltered spot. Store in boxes of slightly damp peat moss, vermiculite, or wood shavings at 40 to 50 degrees Fahrenheit. Check monthly through winter and mist lightly if tubers appear shriveled. Fresh-cut dahlias last four to six days in a vase.

Troubleshooting Common Problems

The most frequent issue is tuber rot caused by planting too early in cold, wet soil or overwatering before shoots emerge. Tall dinner-plate varieties topple without staking, so install supports at planting time. Dahlias may fail to bloom if overfertilized with nitrogen or if planted in too much shade. Spider mites can become problematic in hot, dry weather, causing stippled and bronzed foliage. In cold climates, improper winter storage leads to shriveled or rotten tubers.

Growing Tips

1. Plant dahlia tubers only after your last frost date when soil temperature reaches at least 15°C (60°F). Cold, wet soil causes tuber rot before shoots ever emerge.
2. Place your stake or support structure at planting time, not after the plant has grown. Inserting a stake later risks spearing the tuber clump and damaging the root system.
3. Do not water tubers at planting time. Wait until green shoots are visible above the soil, then begin watering gradually. Overwatering dormant tubers is the leading cause of failure.
4. Pinch the central growing tip when plants reach about 30 cm tall and have three to four pairs of leaves. This encourages branching and can double the number of flowers produced.
5. Feed with a low-nitrogen fertilizer such as 5-10-10 or 10-20-20. Excess nitrogen produces lush foliage at the expense of blooms. Switch to a higher-potassium feed once buds appear.
6. For the biggest possible blooms on dinnerplate varieties, disbud by removing the two smaller side buds at each stem tip, directing all the energy into the central flower bud.
7. Cut flowers in the early morning when stems are fully hydrated. Cut to a length just above a leaf node and immediately place stems in hot water (60°C) for one hour to seal the stems and extend vase life.
8. After the first killing frost blackens the foliage, wait five to seven days before lifting tubers. This brief curing period in the ground toughens the tuber skin and improves winter storage success.
9. Store lifted tubers in a cool, dark place at 4-7°C in slightly damp peat moss or vermiculite. Check monthly throughout winter and discard any showing signs of rot to protect the rest of the collection.
10. Grow dahlias in full sun with at least six to eight hours of direct sunlight daily. In extremely hot climates with temperatures regularly above 35°C, provide light afternoon shade to prevent heat stress and flower fading.