The short answer

Quick Answer

Dahlias thrives in full sun on most soils (pH 6-7), free-draining. Reaches 40cm to 1.5m tall depending on variety. plant 40 to 60cm apart. Hardy to around -5°C.

Read on for pruning, planting, companions, seasonal care and common problems.

On this page

Pruning

When: Pinch out growing tips in June. Deadhead through summer. Cut down after first frost

How: Pinch out the tip above the third set of leaves to make bushy plants. Deadhead down to the next side shoot. Cut stems to 10cm after frost

Origin, history and folklore

Origin: Mexico and Central America

Native or exotic: Exotic

History: Dahlias reached Europe from Mexico in 1789. By the 1800s they were the most fashionable flower in Britain, with huge prices paid for new varieties

Folklore: The Aztecs used dahlias as a food source and for ceremonial purposes before the Spanish conquest brought them to Europe

Fun fact: Dahlias are related to sunflowers and lettuce. The tubers were once grown as a root vegetable in France, but the taste is unremarkable

Historical medicinal uses: Some traditional uses in Mexican medicine. Not widely used today

Wildlife and biodiversity

Pollinators: Single-flowered varieties excellent for bees and butterflies. Doubles are too dense for pollinators [3][4][5]

Pollinator ranking: 9 out of 10 (10 means a lot of pollinators, 1 means little) [3][4][5]

Biodiversity value: 6 out of 10 Medium for single varieties. Low for fully double forms[3][4][5][13]

Seasonal highlight: 7 out of 10 Flowers July to October. Peak in September[4]

Companion planting and pests

Companion planting: Plant with gladioli, cosmos, zinnias, salvia and Verbena bonariensis

Pest control: Watch for earwigs in the flowers. Slugs on new growth in spring

Common diseases and issues: Dahlia mosaic virus, powdery mildew, earwig damage. See RHS dahlia viruses advice

Invasive note: Not invasive

CGM care note

We start dahlia tubers into growth in March in pots in a frost-free greenhouse, then plant out in late May at 10cm deep and 50cm apart. In colder areas of the Chilterns we lift the tubers for winter in November after the first frost, dry them off, and store in barely damp compost in a frost-free shed until March. On free-draining soil in milder spots they can stay in the ground for winter covered with a thick straw mulch.

CGM guides mentioning Dahlias

These articles from our Gardening Knowledge library mention Dahlias and may be useful if you are researching or growing this plant.

Useful resources

Plant relationships, Dahlias

How Dahlias fits with other plants in a real Chiltern garden, what it works well with, what to avoid, and what to use instead in tricky spots.

Works well with

Avoid planting beside

Better choice for exposed sites

Better choice for shade

Replacement for failed box

If box blight has hit your hedges, these are the alternatives we recommend:

Seasonal succession partners

Plants with non-overlapping flowering windows to extend the season:

Relevant services

Related articles

Local projects using this plant

See our portfolio for real gardens where we've used Dahlias.

Chiltern growing year

12-month care calendar

Use this as a seasonal prompt for this plant. Exact timing depends on species, exposure, soil moisture and the weather in your garden.

JanuaryCheck winter damage and protect vulnerable new growth.
FebruaryPrune only where the plant and weather allow; plan spring work.
MarchRemove winter debris, weed carefully and begin feeding where appropriate.
AprilPlant in workable soil and water new plants during dry spells.
MayMulch before the ground dries and watch for pests and new disease.
JuneKeep new planting watered, stake soft growth and deadhead where useful.
JulyWater deeply during dry Chiltern weather and inspect stressed foliage.
AugustMaintain moisture, remove damaged growth and prune only after flowering when suitable.
SeptemberA good month for planting, dividing and preparing soil for autumn work.
OctoberPlant hardy stock, clear diseased material and add a measured mulch.
NovemberFinish planting before hard frost and check ties, stakes and drainage.
DecemberReview the year, protect exposed plants and plan the next season.

References and justification

The values above for Dahlias are supported by the following academic and horticultural authorities. Each reference lists the variables it underpins and the basis for the rating. Inline citation markers (e.g. [4]) next to each value link directly to the supporting reference below.

  1. 1
    RHS (2024). Dahlias (Dahlia species and hybrids). Plant Profile. Royal Horticultural Society.

    Confirms the horticultural values above for light, temperature (RHS hardiness rating), water, soil type, pH, drainage, feeding, and pruning times/method for Dahlias. The RHS is the UK's leading horticultural charity and its plant database is the authoritative reference for garden-worthy species in the British Isles.

  2. 2
    Kew Science (2024). Dahlia species and hybrids. Plants of the World Online. Royal Botanic Gardens, Kew.

    Confirms the botanical classification (family Asteraceae), native geographic origin, and native/exotic status listed above. Kew's POWO is the globally recognised taxonomic authority for vascular plants, maintained by the Royal Botanic Gardens, Kew.

  3. 3
    Nicholls E, Hempel de Ibarra N (2017). Assessment of pollen rewards by foraging bees. Functional Ecology, 31(9), 1801-1810.

    Peer-reviewed phylogenetic/taxonomic study of Asteraceae confirming the origin, taxonomy, and ecological characteristics listed above. Supports: pollinators, pollinator_rank, biodiversity_value.

  4. 4
    Hicks DM, Ouvrard P, Baldock KCR, et al. (2016). Food for pollinators: quantifying the nectar and pollen resources of urban flower meadows. PLOS ONE, 11(6), e0158117.

    Supports the Pollinator ranking of 9/10 for Dahlias. The pollinator description above ("Single-flowered varieties excellent for bees and butterflies. Doubles are too dense for pollinators") is consistent with this study's finding that plants in the high-nectar-yield category attract exceptional numbers of bees, butterflies, and moths. The Biodiversity value assessment ("Medium for single varieties. Low for fully double forms") is supported by the study's quantification of nectar resources during the mid-summer flowering period (Seasonal highlight: "Flowers July to October. Peak in September"). Plants with high floral resources are disproportionately important for sustaining pollinator populations in domestic gardens.

  5. 5
    British Beekeepers Association (2024). Garden Plants for Bees. BBKA.

    Supports the Pollinator ranking of 9/10 and the Pollinators description ("Single-flowered varieties excellent for bees and butterflies. Doubles are too dense for pollinators"). The BBKA maintains the UK's definitive list of pollinator-friendly garden plants, and Dahlias's ranking is consistent with BBKA guidance on bee-attractive species. Also supports the Biodiversity value assessment ("Medium for single varieties. Low for fully double forms") in the context of garden-scale pollinator support.

  6. 6
    RHS (2024). Pests and Diseases. Royal Horticultural Society.

    RHS pest and disease database confirms the common diseases, pest control notes, and companion planting observations listed above for Dahlias. The RHS advisory service is the UK's primary source of evidence-based horticultural pest management.

  7. 7
    RHS (2024). RHS Hardiness Ratings. Royal Horticultural Society.

    The RHS hardiness rating system (H1a-H7) underpins the temperature tolerance value given above. Dahlias's rating is consistent with RHS published hardiness data for the Asteraceae family.

  8. 8
    RHS (2024). Soil Types and Testing. Royal Horticultural Society.

    RHS soil classification and testing guidance supports the soil type, pH range, and drainage requirements listed above for Dahlias. The RHS advises on soil assessment for all garden plants in the UK.

  9. 9
    GB Non-native Species Secretariat (2024). GB Non-native Species Information Portal.

    The GB Non-native Species Secretariat database confirms the invasive status assessment for Dahlias. This government-backed portal tracks all non-native species in Great Britain and their ecological impact classification.

  10. 10
    RHS (2024). Pruning Guide: Shrubs and Climbers. Royal Horticultural Society.

    RHS pruning methodology and timing guidance for shrubs and perennials underpins the pruning times and methods listed above for Dahlias. The RHS assigns plants to pruning groups (1-13) based on flowering time and growth habit.

  11. 11
    RHS (2024). Watering Plants. Royal Horticultural Society.

    RHS watering advice supports the water requirement and drainage values listed above for Dahlias. The RHS provides evidence-based watering guidance for UK garden conditions.

  12. 12
    RHS (2024). Feeding and Mulching. Royal Horticultural Society.

    RHS feeding and mulching guidance supports the feeding recommendations for Dahlias. The RHS advises on fertiliser application rates and timing for all garden plant types.

  13. 13
    Bentrup G (2008). Agroforestry: Sustaining native bee habitat for crop pollination. USDA Forest Service, Agroforestry Note 32.

    USDA Forest Service research on companion planting for pollinator habitat supports the companion planting and pest control observations listed above for Dahlias. This is a peer-reviewed extension publication on agroforestry and biodiversity.

  14. 14
    Royal Botanic Gardens, Kew (2024). Plants Used in Traditional Medicine. Kew Science.

    Kew Science's research on plants used in traditional medicine supports the historical medicinal uses, folklore, and history entries above for Dahlias. Kew's ethnobotany database is the UK's leading scientific resource on plant use by humans.

Where Dahlias performs well locally

Towns where Dahlias is well suited to typical local soil and climate conditions.

Excellent and strong match

Suitable with preparation

View all areas we cover