Dahlia

Sun

Full sun, ideally at least 6 hours daily; light afternoon shade helps in very hot climates.

Water

Water deeply when the upper soil begins to dry during active growth. Keep dormant tubers barely moist and never waterlogged.

Soil

Fertile, well-drained soil enriched with compost; avoid ground that stays wet in winter.

Height

3-5 ft (0.9-1.5 m)

Spread

1.5-3 ft (0.45-0.9 m)

Flowers

Summer to the first autumn frost; typically pink to purple rays surrounding a yellow centre. Garden hybrids include white, yellow, orange, red and many mixed colours.

Foliage

Green, toothed leaves divided into broad leaflets on upright, branching stems; top growth dies with frost.

Growth

Fast during the growing season, reaching flowering size in one season.

Care needed

High

• Plant outside after frost danger has passed and the soil has warmed, with the tuber crown just below the surface.
• Place stakes at planting time and tie growing stems loosely before they become top-heavy.
• Water at soil level during dry spells; avoid repeatedly soaking newly planted, unsprouted tubers.
• Apply a balanced fertiliser according to its label once growth is established; avoid heavy nitrogen feeding.
• Mulch established plants to conserve moisture, keeping mulch clear of the stems.
• In cold or winter-wet areas, lift tubers after frost blackens the foliage and store them somewhere frost-free.

Pruning. Pinch out the growing tip when plants are about 12-16 in (30-40 cm) tall to encourage branching, and remove faded flowers back to a strong leaf joint. After frost kills the foliage, cut stems down before lifting or protecting the tubers.

Late winter

Inspect stored tubers and remove any that are soft or rotting; lightly moisten packing material if sound tubers are shrivelling.

Early spring

Pot up tubers under frost-free cover if you want an earlier start.

Late spring

Harden off young plants, then plant outside after the last frost and install stakes.

Early summer

Pinch growing tips, tie stems to supports and begin regular watering as growth accelerates.

Summer to autumn

Deadhead or cut flowers regularly, water during dry weather and check new shoots for pests.

Late autumn

After frost blackens the foliage, lift tubers where winters are cold or wet; dry their surfaces and store cool but frost-free in barely moist packing material.

• Plant through sunny mixed borders with salvias and ornamental grasses for strong late-season colour.
• Grow in a cutting bed or potager, where supports and regular harvesting are easy to manage.
• Use repeated groups along a path or fence to carry flower colour into autumn.
• Place behind lower-growing border plants to hide the lower stems and frame the flowers.

Garden styles it suits: Cottage garden, English country, Potager (kitchen garden), Romantic rose garden, Hot border and Autumn colour.

Plant it with: Salvias, Tall verbena, Cosmos, Catmint, Switchgrass and Zinnias.

Wildlife: Open, single flowers provide accessible pollen and nectar for bees and other insects. Densely double garden forms offer much less accessible food.

• Slugs and snails eat emerging shoots: check plants at dusk, remove hiding places and use a labelled control where necessary.
• Aphids cluster on soft growth: wash off small colonies with water and encourage ladybirds and other predators.
• Powdery mildew coats leaves in dry, crowded conditions: improve spacing, water the root zone consistently and remove badly affected foliage.
• Tubers rot in wet soil or storage: improve drainage, discard soft tubers and keep stored clumps cool, frost-free and only barely moist.

Dahlias are mildly toxic to cats and dogs; chewing plant material, including leaves, stems or tubers, can cause stomach upset, and contact can cause mild dermatitis. Toxicity to horses is not well established. They are not known to be seriously poisonous to people, but sap can irritate sensitive skin; do not assume ornamental plants are safe to eat.

• Zinnia (Zinnia elegans)

  Zinnias have rough, simple, undivided leaves rather than the divided leaves typical of Dahlia pinnata; they are annuals without tuberous storage roots.

• Garden chrysanthemum (Chrysanthemum × morifolium)

  Chrysanthemums have lobed, often strongly scented leaves rather than separate toothed leaflets, and usually carry many smaller flower heads on bushier stems.

• Garden cosmos (Cosmos bipinnatus)

  Its pink or purple flowers can resemble single dahlias, but its foliage is finely divided into threadlike segments rather than broad leaflets.

Dahlia honours Swedish botanist Anders Dahl, while pinnata refers to the feather-like arrangement of the leaflets.

Propagation. Divide tuber clumps in spring as buds become visible, keeping at least one live eye and a piece of crown attached to each division. Basal cuttings taken from new shoots also work well. Seed-grown plants vary and do not reliably reproduce a named garden form.

Accepted botanical name

Dahlia pinnata

In the US and Canada

Introduced in the lower 48 states.

Native range

Mexico Central, Mexico Gulf, Mexico Northeast and Mexico Southwest.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.