Thomas A. Edison dahlia
Dahlia 'Thomas A. Edison'. Family Asteraceae. Bulb.
Also called Thomas Edison dahlia.
Dahlia 'Thomas A. Edison' is a tuberous perennial grown for its large, fully double, deep purple flowers from summer until frost. It makes a substantial border plant and a useful cut flower, but needs support and frost protection. In cold climates it is grown as an annual or its tubers are lifted and stored indoors for winter.
At a glance
- Sun
- Full sun; light afternoon shade can help in very hot climates.
- Water
- Water deeply when the surface soil begins to dry during active growth. Keep moisture reasonably even, but avoid waterlogged soil, especially around dormant tubers.
- Soil
- Fertile, well-drained soil enriched with compost; tolerates slightly acidic to slightly alkaline conditions.
- Height
- 3-4 ft (0.9-1.2 m)
- Spread
- 1.5-2 ft (0.45-0.6 m)
- Flowers
- Summer to the first autumn frost; deep purple, fully double flowers, usually 6-8 in (15-20 cm) across.
- Foliage
- Green, divided leaves with broad, toothed leaflets on upright, branching stems; killed by frost.
- Growth
- Fast during the growing season.
- Care needed
- High
The year at a glance
- Heat tolerant
- Low allergen
| J | F | M | A | M | J | J | A | S | O | N | D | |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Flowers | ||||||||||||
| Plant |
Northern hemisphere months. In Australia, shift them by six.
- Difficulty
- Hard
- Toughness
- Needs looking after
Will it suit your garden?
Pick your zone, country, light and whether you have pets.
Full sun is 6 or more hours of direct sun a day, part shade 3 to 6 hours, shade under 3.
How it grows
Planting day
0.5 ft (0.15 m)
After 1 year
3 ft (1.1 m)
full size
Full size in one season.
From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.
Good to know
- Cats and dogs
- Mildly toxic: may upset a stomach
- Growth rate
- Fast
Care
Jobs through the year
- WaterMay–Jun, every 7 days
- Begin deep watering after shoots emerge; avoid soaking newly planted, unsprouted tubers.
- WaterJul–Aug, every 4 days
- Keep established plants evenly moist at root level; skip after rain and increase during heat.
- WaterSep–Oct, every 7 days
- Water during dry spells while actively growing; stop when frost kills the tops.
- FeedJun–Sep, every 28 days
- Apply balanced flowering-plant fertilizer at label rates; avoid excessive nitrogen.
- MulchJun
- Mulch established plants after soil warms, leaving stems clear.
- PruneJun
- Pinch the growing tip at 30–40 cm tall to encourage branching.
- ProtectMay–Oct, every 7 days
- Install strong stakes at planting, adjust ties and inspect shoots for slugs and aphids.
- DeadheadJul–Oct, every 7 days
- Cut faded flowers back to a strong pair of leaves.
- PruneOct–Nov
- Cut down frost-blackened stems before lifting the tubers.
- ProtectOct–Nov
- Lift after killing frost, surface-dry and store frost-free in barely moist packing.
- ProtectJan–Apr, Dec, every 30 days
- Check stored tubers for rot or shrivelling and adjust packing moisture sparingly.
- Plant tubers after frost danger has passed and the soil has warmed; avoid heavy watering until shoots appear.
- Install strong stakes at planting and tie stems loosely as they grow.
- Water at soil level during dry weather, soaking the root zone rather than wetting the flowers.
- Feed with a balanced flowering-plant fertilizer once growth is established, following label rates; avoid excessive nitrogen.
- Mulch established plants to conserve moisture, keeping mulch away from the stems.
- Where winter freezes are likely, lift tubers after frost blackens the foliage, dry their surfaces, and store frost-free in barely moist packing material.
Pruning. Pinch out the growing tip when plants are about 12-16 in (30-40 cm) tall to encourage branching, and remove spent flowers back to a strong pair of leaves. After frost kills the top growth, cut stems down before lifting or winter mulching.
Through the year
- Early spring
- Check stored tubers for rot or shrivelling; pot up under cover if you want an earlier start.
- Late spring
- Plant outdoors after frost danger has passed, adding stakes before roots spread.
- Early summer
- Pinch young plants, begin feeding, and tie new stems to their supports.
- Summer
- Water during dry spells and remove faded flowers regularly.
- Autumn
- Keep deadheading and check ties as heavy flowers and autumn winds strain the stems.
- Late autumn
- After the first killing frost, lift tubers in cold regions; in mild regions, leave them only in freely drained soil with protective mulch.
- Winter
- Inspect stored tubers periodically, removing rotten material and lightly moistening packing if tubers begin to shrivel.
In the garden
- Place in the middle or back of a sunny mixed border for strong late-season colour.
- Combine with orange crocosmias or rudbeckias for a purple-and-gold contrast.
- Pair with airy grasses and salvias to soften the large, dense flower heads.
- Grow in a dedicated cutting bed with sturdy supports and easy access for maintenance.
Garden styles it suits: Cottage garden, English country, Traditional, Romantic rose garden, Hot border and Autumn colour.
Plant it with: Salvia, Verbena, Rudbeckia, Crocosmia, Cosmos and Feather reed grass.
Wildlife: The densely double flowers provide much less accessible pollen and nectar than single-flowered dahlias. Choose open-centred flowers nearby to support bees and other pollinators.
Problems to watch for
- Slugs and snails eat emerging shoots: inspect at dusk, remove hiding places, and use an approved iron-phosphate bait if needed.
- Aphids cluster on soft growth: wash off small colonies with water and use insecticidal soap if infestations persist.
- Powdery mildew coats leaves in dry, crowded conditions: improve airflow, water the root zone consistently, and remove badly affected foliage.
- Tubers rot in wet soil or damp storage: improve drainage, let lifted tubers dry on the surface, and discard soft or foul-smelling material.
Safety
Dahlias are mildly toxic to cats and dogs; ingestion of plant material can cause stomach upset, and contact may cause skin irritation. They are not known to be toxic to horses or people, although handling the sap can irritate sensitive skin.
Easily confused with
Purple Gem dahlia (Dahlia 'Purple Gem')
Also purple, but its narrow, rolled cactus-type petals give a spiky outline; 'Thomas A. Edison' has broad decorative-type petals and a fuller, rounded flower.
The name
Dahlia honours the Swedish botanist Anders Dahl, and the cultivar name honours the American inventor Thomas Alva Edison.
Propagation. Divide tuber clumps in spring, ensuring each division has a piece of the crown with a viable eye; a detached tuber without an eye will not grow. Basal cuttings from fresh spring shoots also preserve the cultivar. Seed-grown plants will not reliably match it.
Checked against open data
- Accepted botanical name
- Dahlia
Sources: GBIF (CC BY 4.0). The care and design notes are LandscapeGPT's own.
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