Ambition Dahlia Tubers

• Variety: Ambition
• Type: Semi-cactus (fimbriata — petals with forked, split tips)
• Colour: Magenta-purple
• Flower size: Up to 15cm (6in) across
• Height: 100cm
• Spread: 60cm
• Flowering: July to November
• Cutting: Excellent — strong upright stems, very good vase life
• Rain resistance: Better than average — cactus petals shed water more readily than flat decorative types
• RHS AGM: No
• Sold as: Single tubers, hand-graded, Dutch first-class quality
• Plant outdoors: March–July, when soil reaches 15°C (typically May in most of the UK)
• Delivered: From March

Ambition Dahlias - Spiky, Purple and Rainproof

Some dahlias can (especially the large decorative ones can collapse into a soggy mess after a heavy shower. Not Ambition. The semi-cactus petals are rolled and quilled rather than flat, so water runs off instead of sitting in the bloom and rotting it from the inside. The petal tips are forked — split like tiny deer antlers — which gives each flower a slightly shaggy, textured look that we think is more interesting than the smooth perfection of a decorative type. The colour is a saturated magenta-purple that holds from first bud to last petal drop, no fading, no shifting.

At 15cm across, the flowers are large enough to hold their own in a border but manageable in a vase. The stems are strong and upright, and Ambition produces masses of blooms from July right through to November. This a tidy, relatively compact dahlia at a metre tall. Plant in groups of three at 75cm spacing and you'll have a solid block of purple from midsummer to the frosts. It's a favourite of Sarah Raven's, which tells you much of what you need to know about its reliability.

Planting Companions

Ambition's saturated purple works best either with similar deep tones or against deliberate contrast. For a rich, moody border, try it with deep red dahlias like Arabian Night and the dark bronze foliage of David Howard in front. For contrast, the warm blush tones of Cafe au Lait or Arbatax (white with pink edges) make the purple sing. Ornamental grasses soften the effect: Stipa tenuissima or bronze Carex catch the light between the flower heads. Verbena bonariensis threads through at the same height and extends the purple upwards.

Why Ashridge?

Our dahlia tubers are Dutch first-class quality, imported direct and hand-graded — we discard undersized tubers so you get a clump with viable eyes, ready to grow. Delivered by next-day courier from March, with our one-year plant guarantee, Feefo Platinum Service Award, and human support from the team in Somerset. Browse our full cactus dahlia range or the complete dahlia collection.

Frequently Asked Questions

What's the difference between a semi-cactus and a decorative dahlia?

Petal shape. Decorative dahlias like Cafe au Lait and David Howard have broad, flat petals that lie open. Semi-cactus types like Ambition have petals that are rolled or quilled for at least half their length, giving a spikier, more textured appearance. The practical difference is rain resistance: rolled petals shed water, flat petals hold it. In a wet British summer, that matters.

Is it really more rain-resistant?

Yes. The quilled petals don't trap water the way flat decorative blooms do, so the flowers are less likely to rot or become waterlogged after heavy rain. They won't survive a prolonged downpour completely unscathed, but they bounce back faster and hold their shape better than most. If your garden is in a wetter part of the UK, cactus and semi-cactus varieties are worth considering for this reason alone.

What are fimbriata petals?

Ambition is sometimes classified as a fimbriata dahlia because the tips of its petals are forked or split — think tiny deer antlers. This gives the flowers a slightly shaggier, more informal texture compared to a smooth-petalled cactus dahlia. It's the same plant either way; fimbriata is just a more specific description of the petal tip.

Does it need staking?

At a metre tall with 15cm flowers, light staking is sensible — a single cane or a support ring put in at planting time. It's less demanding than the taller dinnerplate varieties, but wind and rain can still push it over if unsupported.

Will it grow in a pot?

Yes. The compact habit and mid-sized flowers suit container growing well. Use a pot at least 35cm across and deep with rich compost, a cane for support, and regular liquid feeding from June. See our growing dahlias in pots guide.

When should I plant, and how deep?

Plant tubers from March onwards, but wait until the soil reaches about 15°C — typically May in most of the UK. Cover the tuber with 10–12cm of soil. If your tubers arrive before the ground is warm enough, pot them up temporarily and keep them frost-free. Full planting and aftercare advice is in our dahlia growing guide.

Do I need to lift the tubers in winter?

In colder or wetter parts of the UK, lifting after the first frost is safest. In milder areas with well-drained soil, a thick mulch of straw or dry leaves over the crown will usually see them through. See our overwinter storage guide for the full method.