How to plant dahlia tubers: depth, spacing and staking
Oct 2, 2026 · 7 min read
How to plant dahlia tubers: lay them on their side 4 to 6 inches deep, eye up, 2 feet apart, in warm soil. Then staking, pinching, feeding and heights by form.
To plant dahlias, wait until the soil has stayed at about 60 °F (16 °C) or warmer for several days in a row, then lay each tuber on its side in a hole 4 to 6 inches (10 to 15 cm) deep with the eye facing up, and space plants about 2 feet (60 cm) apart. That is the recommendation in Oregon State University’s dahlia fact sheet FS 95.
Soil temperature before planting
Plant dahlia tubers (most catalogs call them bulbs) in late spring, after the ground has warmed and frost is unlikely. The American Dahlia Society suggests planting in the same window you would plant tomatoes. In western Oregon, OSU puts that between late April and the end of May.
Go by soil temperature rather than the calendar. A soil thermometer pushed to planting depth answers the question in a few mornings.
Use your last frost date as the starting point
Your last spring frost tells you roughly when the soil will get there. The spring flower planting calendar gives the earliest date for your ZIP code, counted from the frost date that only one year in ten runs past; plant after it, once the soil thermometer agrees.
Is it too late to plant dahlias?
Usually not. The ADS says dahlias can go in as late as mid-June in most parts of the country. Late planting pushes the first flowers later into summer, but dahlias bloom until frost, so you still get a season out of them. Check your first fall frost date if you are planting very late in a short-season area.
Where to plant dahlias
Pick a spot with at least six hours of direct sun. OSU gives six hours as the minimum to maximize blooms, and the ADS lists partial to full sun with good drainage. If water stands in the bed for long after a rain, pick another spot.
OSU gives a soil pH range of 6.5 to 7.0. If you have never tested your soil, a basic test through your county extension office will tell you where you stand before you start adding lime or sulfur.
How deep to plant dahlia tubers
Dig a hole about 4 to 6 inches (10 to 15 cm) deep. Lay the tuber horizontally with the eye, the small bud near the old stem where the sprout will come from, pointing up. Cover it with soil and firm it lightly.
How far apart to plant dahlias
Space dahlias about 2 feet (60 cm) apart. Both OSU and the ADS give the same figure. The plants fill out much more than a bare tuber suggests, and air moving between them helps the leaves dry after rain.
Put the stake in before the tuber
If the variety will grow taller than about 3 feet, drive the stake in at planting time, next to the hole, and set the tuber beside it. The ADS recommends placing a sturdy stake before planting, because pushing one in later can spear a tuber you can no longer see. More on staking below.
Should you water dahlia tubers after planting?
Not right away: OSU says not to water until the first two leaves have appeared. OSU says tubers are susceptible to rot at this stage. Plant into slightly moist soil, and if the soil is dry, dampen it lightly.
Once plants are growing, the ADS rule of thumb for larger plants is to water when rainfall falls short of about 1 inch (2.5 cm) in seven days.
How tall do dahlias grow?
Dahlia heights vary widely. Height depends on the variety far more than on the flower form, but some forms run shorter or taller than others. These ranges come from the height listed for each variety in our dahlia catalog, grouped by the form the American Dahlia Society uses to classify them:
| Form | Height range in our catalog | Example |
|---|---|---|
| Informal decorative | 12 to 60 in (30 to 152 cm) | Gallery Singer, Imperial Wine |
| Formal decorative | 30 to 60 in (76 to 152 cm) | Black Satin |
| Waterlily | 24 to 51 in (61 to 130 cm) | Firepot |
| Collarette | 36 to 54 in (91 to 137 cm) | Bee Happy |
| Semi-cactus | 31 to 48 in (80 to 122 cm) | Yellow Star |
| Ball | 30 to 42 in (76 to 107 cm) | Brown Sugar |
| Pompon | 36 to 42 in (91 to 107 cm) | Chick A Dee |
The informal decorative row has the widest spread because it includes both the Gallery series, bred as compact border and pot plants, and big cut-flower varieties like Café au Lait. Pompons are small flowers on full-size plants, so a small bloom does not mean a short plant.
What about dinnerplate dahlias?
“Dinnerplate” describes flower size, not flower form. A large-flowered dahlia can belong to any of several forms. To find tall or short plants, filter the dahlia catalog by height.
Which dahlias grow well in pots?
Low-growing and dwarf varieties are the best choices for containers, according to OSU. Use a pot 12 to 18 inches (30 to 45 cm) deep and wide, and expect to fertilize about every two weeks. The short Gallery types, such as Gallery Pablo, and the miniature ball Wizard of Oz are the shortest plants in the catalog.
How to stake dahlias
OSU says dahlias taller than 36 inches (90 cm) usually need stakes, and the stakes should be at least 4 to 5 feet (1.2 to 1.5 m) tall. The ADS says most dahlias need staking and suggests tomato cages as a simple alternative.
Tie the main stem to the stake loosely with soft twine or strips of cloth as the plant grows.
Pinching dahlias for more flowers
Pinch the growing tip once the plant is 12 to 16 inches (30 to 40 cm) tall. OSU’s instruction is to pinch off the sprout between the top pair of leaves, which pushes growth into the side shoots at the leaf nodes below.
Feeding dahlias after planting
Hold off on fertilizer for the first month. OSU says applications can begin 30 days after planting and continue every three to four weeks as needed. The ADS notes the traditional approach of feeding with more nitrogen through midseason and cutting nitrogen back toward the end of the season, when the plant should be building tubers for next year.
What happens to dahlias in fall
Dahlias are tender. The tuberous roots do not survive cold winters in the ground, and in cold climates they need to be dug and stored indoors. The University of Wisconsin recommends digging before a hard freeze or after a light frost has blackened the tops. Our guide on how to store dahlia tubers walks through digging, drying, storage and dividing, and the bulb planting tool gives a digging window by ZIP code.
If you are deciding whether to treat dahlias as a one-season plant or a keeper, annuals vs. perennials explains where they fit. Planting a cutting bed? Zinnias go in around the same time and fill the gap before the first dahlias open.
Quick planting checklist
- Soil at about 60 °F (16 °C) for several days in a row, after your last frost
- Six or more hours of sun, soil that drains
- Holes 4 to 6 inches (10 to 15 cm) deep, 2 feet (60 cm) apart
- Tuber on its side, eye up
- Stake in the ground before the tuber for plants over 3 feet
- No water until the first leaves show
- Pinch at 12 to 16 inches (30 to 40 cm), fertilize from day 30