King Arthur Dahlia Tubers

• Variety: King Arthur
• Type: Decorative (small-flowered)
• Colour: Deep velvet red, near-black at the centre
• Flower size: 10–12cm (4–5in)
• Height: 90–100cm
• Spread: 45–50cm
• Flowering: July to first frosts
• Cutting: Yes. Strong upright stems, good vase life
• RHS AGM: No
• Sold as: Single tubers, hand-graded, Dutch first-class quality
• Plant outdoors: March to July, when soil reaches 15°C (typically May in most of the UK)
• Delivered: From March. Collection from Castle Cary also available

Dahlia King Arthur – Deep Velvet Red

King Arthur is one of those dahlias where the colour does all the work. Deep velvet red, darkening almost to black at the centre, with a surface sheen that shifts between burgundy and chocolate depending on how the light catches it. Photographs don't do it justice. They flatten the depth into a generic dark red, whereas in the garden you're looking at something closer to crushed velvet. It's a small-flowered decorative at 10–12cm across, which means masses of blooms rather than a handful of dinner plates.

The plant reaches about a metre tall, upright and sturdy. Strong stems hold the flowers well above the foliage without flopping. Useful if you're cutting for the house, which you will be. Pick them fully open (dahlia buds stop developing once cut) and you'll get five to seven days in a vase. A single stem in a dark bottle on a windowsill is better than most shop-bought bouquets.

King Arthur for Cutting

Small-flowered decoratives tend to make better cut flowers than the show-stopping dinnerplates, and King Arthur is a good example. The stems are stiff, the heads face outwards rather than drooping, and the colour holds well indoors without bleaching. Strip the lower leaves, stand stems in hot water for an hour, then move to a clean vase. Refresh the water every couple of days. The deep red works with almost any vessel: copper jugs, white ceramics, a jam jar. Deadhead regularly through summer and you'll have cutting material from July until the first hard frost.

Planting Companions

King Arthur's deep red pairs well with warm oranges and bronzes. David Howard planted alongside gives you burnt orange against dark red, with David Howard's chocolate-bronze foliage tying the scheme together. For a richer, darker planting, add Nescio, the blood-red pompon — it picks up King Arthur's colour in miniature form. Silver or grey foliage provides the sharpest contrast: lavender at the front of the border cools the whole scheme down and gives you scent alongside colour. For something taller behind, Rip City echoes the dark red in semi-cactus form.

Why buy from Ashridge?

Our dahlia tubers are Dutch first-class quality, imported and hand-graded by us. We throw away undersized tubers so you get a clump with plenty of viable eyes (growth buds), ready to go. Delivered by next-day courier from March, with our one-year plant guarantee and human support from the team in Castle Cary if anything goes wrong. Browse the full dahlia collection.

Frequently Asked Questions

Is King Arthur a good dahlia for beginners?

Yes. Plant the tuber after the last frost, stake with a single bamboo cane, deadhead regularly, and you'll have flowers from July until November. The upright, compact habit means it doesn't need the heavy staking that taller dinnerplate varieties demand. Our dahlia growing guide covers the full detail.

How do I overwinter King Arthur dahlia tubers?

Lift them after the first frost has blackened the foliage. Cut the stems to about 15cm, shake off loose soil, and dry the tubers upside down for a week. Store in slightly damp compost in a frost-free place — a garage, shed, or unheated spare room works. Check monthly through winter for rot or shrivelling, and replant when the soil warms up in spring. Our overwintering guide has the full method.

How deep should I plant King Arthur dahlia tubers?

Plant 10–15cm deep with the eyes (growth buds) facing upwards. If you can't see obvious eyes, don't worry — plant the tuber on its side and the shoots will find their own way up. Water in well and then leave it alone until you see growth. Our tuber eyes and crowns guide explains what to look for.

Will King Arthur dahlia grow in a pot?

Yes. At around a metre tall with small flowers, it doesn't become top-heavy the way larger varieties do. Use a pot at least 30cm across with rich, free-draining compost and feed fortnightly with a liquid fertiliser from June. See our dahlias in pots guide for full instructions.

What is the difference between King Arthur and Bishop of Llandaff?

Both are dark-flowered dahlias but they're quite different plants. King Arthur is a fully double decorative with deep velvet-red petals packed tight. Bishop of Llandaff is a semi-double peony type with open scarlet flowers and a visible central disc, much better for pollinators. The Bishop also has near-black foliage, which King Arthur doesn't. Both are excellent; the choice comes down to whether you want formal double blooms or an open, wildlife-friendly flower.