When should I plant dahlia tubers?

Plant dahlia tubers outdoors after all danger of frost has passed and the soil has warmed to at least 60 degrees, usually mid-to-late spring, around the same time you would plant tomatoes. Dahlias are frost-tender and tubers can rot in cold, wet soil, so patience pays. To get a head start in shorter-season areas, start tubers in pots indoors four to six weeks before your last frost date, then transplant them out once the weather settles.

Do I have to dig up dahlias every year?

In USDA zones 8 and warmer, you can usually leave dahlia tubers in the ground over winter with a heavy mulch. In zones 7 and colder, the tubers will freeze and rot if left in the ground, so you must dig (lift) them after the first frost blackens the foliage and store them somewhere cool and frost-free until spring. Lifting also lets you divide clumps, which multiplies your plants and keeps them vigorous year after year.

How do I get more blooms from dahlias?

Three practices dramatically increase blooms: pinch out the growing tip when the plant is about 12 inches tall to force bushier branching and more flower stems; deadhead spent flowers regularly, since dahlias stop blooming once they set seed; and feed with a low-nitrogen, higher-potassium and phosphorus fertilizer from midsummer. Too much nitrogen gives leafy plants with few flowers. Consistent water and full sun round out the recipe for a plant that blooms from midsummer until frost.

Why are my dahlias not flowering?

The usual culprits are too little sun, too much nitrogen, no pinching or deadheading, or planting too late in the season. Dahlias need at least six to eight hours of direct sun to bloom well. High-nitrogen fertilizer produces foliage instead of flowers. Without deadheading, plants set seed and quit. And in short-season climates, a late start means the plant is still building size when frost arrives. Correct the sun and feeding first, then commit to regular deadheading.

How deep and far apart do I plant dahlias?

Plant dahlia tubers 4 to 6 inches deep, laid on their side with the growing eye (the small bump near the old stem) facing up. Space smaller bedding dahlias about 12 inches apart and large dinnerplate types 18 to 24 inches apart to allow airflow, which reduces powdery mildew. Drive the stake in at planting time to avoid spearing the tuber later. Do not water heavily until you see shoots emerge, as wet soil around a dormant tuber invites rot.

How to Grow Dahlias: Tubers to Blooms, Planting to Storage

Written & researched by Elena Marsh Gardening & Landscaping Editor

Updated February 2026

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The short answer: to grow dahlias, plant tubers outdoors after the last frost in full sun, 4 to 6 inches deep with the eye facing up, in rich, well-drained soil. Stake tall varieties at planting, pinch the growing tip at 12 inches for bushier plants, water deeply once shoots appear, and deadhead relentlessly. In zones 7 and colder, lift and store the tubers indoors over winter. Dahlias bloom from midsummer until the first hard frost, producing more cut flowers per square foot than almost anything else.

Dahlias reward attention like few other flowers, cycling out blooms for months if you keep cutting. Growers consistently report that the three habits separating a spectacular dahlia patch from a mediocre one are pinching, deadheading, and staking. We do not test tubers or supplies first-hand; our guidance reflects aggregated grower reviews and horticultural consensus, described in how we rank.

Choosing dahlia varieties

Dahlias range from compact border plants to dinnerplate giants with blooms the size of a face, and the type shapes spacing, staking, and use.

Type	Height / bloom size	Best for
Dinnerplate	4-5 ft, blooms 8-12 in	Showstopping specimens, focal points
Decorative / ball	3-4 ft, blooms 3-6 in	Cut flowers, borders
Cactus / semi-cactus	3-4 ft, spiky petals	Texture and drama in bouquets
Pompon	3-4 ft, small round blooms	Long-lasting cut flowers
Bedding / dwarf	12-20 in	Containers, edging, front of border

If cut flowers are your goal, decorative, ball, and cactus types offer the best combination of stem length and vase life. For containers or small spaces, choose dwarf bedding dahlias, which need no staking.

When and where to plant

Dahlias are frost-tender tropicals grown from tubers, so timing centers on frost and soil temperature. Wait until all frost danger has passed and the soil has warmed to at least 60 degrees — the same cue as planting tomatoes. Cold, wet soil rots dormant tubers before they sprout, so resist planting early.

Choose a site with full sun, at least six to eight hours, and well-drained soil. Dahlias will not tolerate soggy ground. In short-season climates (zones 3 through 5), start tubers indoors in pots four to six weeks before the last frost to gain flowering time, then transplant after the weather settles.

Soil preparation for dahlias

Dahlias flower best in rich, fertile, well-drained soil with a slightly acidic to neutral pH of 6.5 to 7.0. Before planting, work in two to three inches of compost to improve both drainage and fertility. In heavy clay, plant in raised beds or add grit, because waterlogged tubers are the most common cause of failure.

Go easy on nitrogen at planting. A soil too rich in nitrogen produces lush foliage and weak stems with few flowers; a phosphorus-forward or balanced amendment is better. You will shift to a bloom-boosting feed later in the season once the plant is established.

Planting tubers step by step

Dig a hole 4 to 6 inches deep. Lay the tuber on its side with the growing eye (a small bump near the base of the old stem) pointing up.
Drive the stake in now, before you cover the tuber, so you do not spear it later.
Space by size: 12 inches for bedding types, 18 to 24 inches for large decorative and dinnerplate varieties to allow airflow.
Cover with soil but do not water yet. A dormant tuber in wet soil rots; wait for shoots to emerge before watering.
Once shoots appear (two to four weeks), begin watering and mulch to conserve moisture and suppress weeds.

That no-water-until-sprouting rule surprises new growers, but it is the single most effective way to avoid tuber rot in spring.

Pinching, staking and supporting

Two early interventions determine how bushy and productive the plant becomes.

Pinch the growing tip when the plant reaches about 12 inches, snapping out the center shoot above the third or fourth set of leaves. This forces side branches, dramatically increasing the number of flower stems.
Stake at planting, then tie the stems loosely as they grow. Tall and dinnerplate dahlias are heavy and brittle, and a single storm can snap an unstaked plant. A grid of stakes and twine works well for a whole bed.

Growers who pinch and stake early consistently report far fuller plants and fewer broken stems than those who skip these steps hoping to save time.

Watering and feeding dahlias

Once established, dahlias are thirsty during their long bloom season. Water deeply two or three times a week, providing an inch or more, and more in heat. Water at the base to keep foliage dry and reduce powdery mildew, which is the most common disease on crowded, poorly ventilated plants.

Shift the feeding as the season progresses. Early on, keep nitrogen moderate. From midsummer, switch to a low-nitrogen fertilizer higher in phosphorus and potassium — the same bloom-supporting logic covered in our guide to choosing the best fertilizer for hydrangeas. Feed every three to four weeks through the flowering season, and stop about a month before your first expected frost.

Deadheading and cutting for the vase

Dahlias are a cut-and-come-again flower: the more you cut, the more they bloom. Once a flower fades, the plant tries to set seed and slows flowering, so deadhead diligently. Learn to tell a spent bloom (which forms a pointed, cone-shaped bud) from an unopened one (round and plump) so you remove the right ones.

For the vase, cut in the cool of morning when blooms are nearly fully open, since dahlias do not continue opening much after cutting. Cut stems long, strip lower leaves, and place in water immediately. Regular cutting for bouquets doubles as deadheading and keeps the plant producing.

Lifting and storing tubers for winter

In zones 8 and warmer, dahlias can overwinter in the ground under a thick mulch. In zones 7 and colder, you must lift and store the tubers or lose them to freezing.

Wait for the first frost to blacken the foliage, then cut stems to a few inches.
Dig carefully a foot out from the stem to avoid slicing tubers, and lift the whole clump.
Brush off soil and cure the clump in a dry, airy spot for a few days.
Divide if desired, ensuring each division has an eye, then pack tubers in barely moist vermiculite, peat, or wood shavings.
Store cool and frost-free, at 40 to 50 degrees, checking monthly for rot or shriveling and adjusting moisture.

Stored well, tubers multiply year after year, turning one plant into many. For more long-blooming perennials to pair with dahlias, see our guides to how to grow daylilies and how to grow sunflowers, or browse the full flowers and ornamentals hub.

How to Grow Dahlias