Dahlia
Dahlia pinnata · Popular
Flowers in every colour but blue and in every form, from single daisies to dinner-plate doubles, from midsummer until frost. In cold climates the tubers are lifted and stored for winter.
- Size
- 3½ ft tall, 24 in wide
- Zones
- 8 to 10
- Light
- Full sun
- Flowers
- Mid July to mid October
- Pets
- Toxic (mild)
- Job in a bed
- Drift
A bed built around dahlia
The planner designed this bed around dahlia when this page was made: a 12 × 6 ft (3.7 × 1.8 m) English border in zone 8, full sun. It chose the other plants from the 872 that suit those conditions, and says below why dahlia stands where it does.
The plants
- 1 Yellow ice plant × 8, yellow
- 2 October daphne × 3, pink
- 3 Little bluestem 'Standing Ovation' × 4, tan
- 4 Italian bugloss 'Dropmore' × 3, blue
- 5 Inkberry 'Gem Box' × 1, dark green leaves
- 6 Purple coneflower × 3, purple
- 7 Dahlia × 1, red
- 8 Star of Persia × 3, purple
Why this plant
- The only red.
Why here
- Forward of its place. At 3½ ft it belongs at the back of the bed: this far forward it stands in the way of what is behind it.
- One plant. Three or more is usual for a plant of this kind, and reads better.
Why now
- In flower for 15 weeks. From mid July to mid October.
- Part of the bed's peak. With Italian bugloss 'Dropmore' and purple coneflower in mid July: 3 kinds at once. No week has more.
Planned as an English border: 6 of the 6 groups (100%) are drifts, longer along the bed than they are deep. Yellow ice plant and October daphne finish the front edge. There is more yellow ice plant than anything else, 8 plants in all.
The planner's own design check: 11 Excellent, 5 Good, 1 Satisfactory. It flags one thing to watch: Nothing on this plan is highly poisonous or an aggressive spreader.
Open this bed in the planner Change its size, the sun or the style, move plants about, or swap one for another.
Where dahlia goes in a border
At 3½ ft it belongs at the back of a bed. In the planner's ten height classes it is moderately tall (3 to 4 ft).
Its job: drift. Planted in a small group of three or five, and repeated further along in the other number.
Nothing flowers harder in late summer. The dark-leaved, single-flowered kinds mix best in a border; the giant doubles are for cutting. They need rich soil, water, staking and deadheading.
- Late-summer and autumn colour
- Cut flowers
- Cottage and tropical-style planting
What to plant with dahlia
Plants recorded as good partners for it, and what each pairing does:
- Canna: purple against yellow, opposite each other on the colour wheel, if you choose those colours, in flower together for 13 weeks; bold leaves against its medium ones; happy in the same moist soil.
- Anise sage 'Black and Blue': blue against orange, opposite each other on the colour wheel, if you choose those colours, in flower together for 15 weeks; grows up in time to hide its dying leaves; happy in the same moist soil.
- Garden phlox: purple against yellow, opposite each other on the colour wheel, if you choose those colours, in flower together for eight weeks; grows up in time to hide its dying leaves; happy in the same moist soil.
Questions about dahlia
Does dahlia need sun or shade?
Dahlia grows in full sun (6 or more hours of direct sun a day).
It wants soil that stays evenly moist, rich in organic matter, and plenty of water.
What zones does dahlia grow in?
USDA zones 8 to 10. It is hardy to zone 8, which means it survives winter nights down to about 20 °F (−7 °C).
Gardening in Canada? Use the USDA zone for your town: Canada's own zone map uses different numbers.
When does dahlia flower in my zone?
In zone 5 it flowers mid July to mid October. As a summer flower it moves about half a week for every zone: earlier where it is warmer.
| Zone 8 | Early July to mid October |
|---|---|
| Zone 9 | Late June to mid October |
Worked out from Hopkins' bioclimatic law: spring arrives about four days later for each degree of latitude north, and one zone is roughly two degrees. A warm spring or a cold one moves any garden two weeks either way.
How far apart should dahlia be planted?
18 in (45 cm) apart, from the middle of one plant to the middle of the next. That is a little closer than its full width of 24 in (60 cm), so a group knits into one patch.
It grows 3½ ft (100 cm) tall. Give it the full distance from anything taller, or it will lean out towards the light.
How many dahlia plants do I need?
At 18 in apart, set out in staggered rows:
- 5 to fill 10 square feet (about 1 m²)
- 7 for a single row 10 ft (3 m) long
- 17 to fill a 4 × 8 ft bed on its own
In a mixed border, plant it as a group of three or five, with a second group further along in the other number.
In the bed above, the planner used one in one group.
Is dahlia poisonous to dogs and cats?
Yes: mild toxicity to people, dogs, cats and horses. Can cause mild stomach upset in pets if eaten. Handling the plant can irritate skin.
Rated from the ASPCA. Where references disagree, the more cautious rating is used.
Is there a pet-safe plant like dahlia?
These come closest to doing what dahlia does, and no toxicity is recorded for them:
- Crocosmia 'Lucifer': the same job in a bed and the same colour; belongs in the middle, not at the back, 10 in narrower.
- Brown-eyed Susan: the same job in a bed and the same flowering time; 8 in taller, yellow, not red.
- Garden phlox 'David': the same job in a bed and the same size; flowers mid July to early September, white, not red.
Matched the way the planner's Swap button matches plants: the same job in a bed, then size, then flowering time.
What can I plant to hide dahlia's leaves after it flowers?
A bulb's leaves have to be left to yellow for about six weeks after flowering, to feed next year's flowers. Plant it among perennials that come up late and spread wide, and they grow over the leaves as they fade:
- Peony: 3 ft tall and 3 ft wide, in flower late May to late June.
- Blue false indigo: 4 ft tall and 4 ft wide, in flower late May to mid June.
- Black-eyed Susan 'American Gold Rush': 24 in tall and 3 ft wide, in flower mid July to early October.
What does dahlia look like in winter?
Dahlia is underground: it dies back after flowering and waits as a bulb until spring. Mark where it is, so a fork does not find it first.
More Dahlia
- Dahlia 'Bishop of Llandaff' Dahlia 'Bishop of Llandaff'
- Dahlia 'Café au Lait' Dahlia 'Café au Lait'
In these guides
Every fact on record
- Type
- Bulb
- Size
- 3½ ft (100 cm) tall, 24 in (60 cm) wide
- Plant
- 18 in (45 cm) apart
- Height class
- Moderately tall (3 to 4 ft)
- Place in the bed
- Back
- Flowers
- Mid July to mid October; daisies; red, pink, orange, yellow, purple, white
- Leaves
- Medium texture, herbaceous; green, burgundy
- Shape
- Upright, clumping
- Hardy in
- USDA zones 8 to 10
- Light
- Full sun
- Soil
- Rich, evenly moist
- Water
- High
- Feeding
- Moderate, in spring
Checked against ASPCA poison lists. Flowering times are for zone 5: later in colder zones, earlier in warmer ones. Toxicity and spread information is a general gardening guide, not veterinary or medical advice, and invasive status varies by region. If a person or pet eats a plant, contact poison control or a vet. Check your local invasive species list before planting anything with a spread warning.