- Common name: Larkspur
- Botanical name: Delphinium
- Family: Buttercup (Ranunculaceae)
- Type: Perennial and annual
- Flowering time: Summer
- Planting time: Spring and autumn
- Height: 1.5-1.8m (5-6ft)
- Spread: 75-90cm (2.5-3ft)
- Aspect: Full sun
- Hardiness: H5
- Difficulty: Average to difficult
- Enemy: Slugs
The best blues in the garden, delphiniums light up the back of the border with immense candles of cobalt, sapphire, and azure. Reaching 1.5 to 1.8 metres, they point towards the blue summer sky and, at their best, outshine every plant in the vicinity. The lesser-known pastel forms are also beautiful and essential perennials in the cottage garden, which is the historic home of delphiniums.
Since at least the fifteenth century, delphiniums were cultivated in cottage gardens. Delphinium staphisagria was widely grown to ward off lice, but by the seventeenth century, D. consolida (syn. Consolida regalis) was planted as an ornamental and cut flower. There are around 300 species of delphinium, native to the Northern Hemisphere, with most hailing from Asia and around ten per cent growing wild in Europe.
The iconic ornamental delphiniums of today were bred from various species, but in particular D. elatum (candle larkspur). In France, the plant breeder Victor Lemoine introduced the first semi-double cultivar in 1852, moving the plants away from more widely spaced blooms on very branching stems, towards the dense flower towers we know and love. In Britain, wonderful hybrids followed from the Kelways and Blackmore and Langdon nurseries in Somerset. Today, Blackmore and Langdon is still a specialist delphinium nursery, run by the great-grandsons of one of the original founders, Charles Langdon, and selling a lovely range of Elatum cultivars.
Which delphiniums to grow
The blue Elatum hybrids that stop you in your tracks by blooming in Côte D’Azur shades of cerulean and cobalt include ‘Blue Nile’ (ultramarine), ‘Langdon’s Pandora’ (azure), ‘Fenella’ (gentian blue), and ‘Molly Buchanan’ (Madonna blue). They are rare in their ability to produce breathtaking bold-blue shades with such magnitude. The downside of this is that they can overly dominate a border. Therefore, in a large garden, they are perhaps best planted in a dedicated delphinium bed, with the most enchanting effect achieved by growing a spectrum of blue shades together: from ‘Faust’ (rich indigo) to ‘Lord Butler’ (Cambridge blue), with a backdrop of evergreens to light them up.
In the midst of an herbaceous border, the intense blues can be tempered by being planted alongside silver and indigo monkshood, cardoon, milky bellflower, giant scabious, and hollyhock ‘Nigra’. Within an exotic-style garden, the glowing blues complement the mass of lush foliage and other bright flora, as does the coral-scarlet delphinium ‘Red Lark’. Unlike the bold-blues, the pastel delphiniums fit effortlessly into cottage-garden borders. They include primrose-cream ‘Sungleam’, pink ‘Rosemary Brock’, and lilac ‘Holly Cookland Wilkins’, which pair well with hollyhocks and bellflowers. Regal-purple and crisp-white varieties (including ‘Purple Velvet’ and ‘Elisabeth Sahin’) are perfect for formal and urban gardens.
If you fancy trying something other than the chocolate-box Elatum hybrids, the perennial Belladonna forms (such as ‘Atlantis’) are superb and make great cut flowers. They look very different from the spire-forming Elatums, having widely spaced blooms on branching stems, as do the easy annual forms: D. grandiflorum and true larkspurs (Consolida). Special Plants nursery offers a range of excellent forms, including the tall North American perennial D. exaltatum and the orchid-like mauve-silver biennial D. requienii, which self-sows.
How to plant delphiniums
Plant delphs in autumn or spring, in neutral to alkaline soil that is sun-baked. Dig in organic matter (such as peat-free compost) because they relish nutrients, moisture, and good drainage. Since their tall stems are hollow, a windy site is best avoided.
How to grow delphiniums
Once the plants surge into growth, supports are vital to prevent the tall stems snapping – these can be manmade or simply four bamboo canes or hazel sticks bound with twine. Being toxic plants, wear gloves to handle delphiniums and plant them at the back of the border, away from pets. Feed and water regularly during the growing season.
Delphinium pests and diseases
Delphiniums are prone to powdery mildew, but providing some air flow and elbow room will help to prevent it. The main problem is slugs, who crave delphs as much as we crave Belgian chocolate; they will make a (very slow) beeline for them and strip their leaves overnight, especially in spring.
Upon enquiring which Elatum hybrids had been the least attractive to slugs in the trial beds at RHS Wisley, the author was informed by one of the supervisors that, ‘we don’t have slugs at Wisley’. For those of us who do have slugs in the garden, unfortunately, it seems that they love eating every Elatum delphinium, and, therefore, these all need guarding with a varied and thorough arsenal.
A ring of grit can be installed around each delphinium during planting to deter slugs underground, and a barrier (such as grit, gravel, or crushed shells) around the plant should be scattered on the surface. Pet-safe slug killers (including organic pellets and Nemaslug) are effective. Comfrey leaves are a non-lethal alternative – the slugs will eat their way through them, never reaching your delphs, as long as the leaves are replaced regularly. Finally, Graham Austin at delphinium nursery Home Farm Plants swears by an annual mulch of horticultural grit, 20-centimetres deep, placed over each plant in winter.
D. requienii is – as far as we are aware – the only garden form that is unappealing to slugs. Until a breeder successfully crosses it with the Elatums to create a slug-resistant marvel, war must be constantly waged on our slimy friends in order to enjoy the classic border delphs. But it is worth it at the height of summer, when you can sit back and gaze at your electric-blue delphiniums soaring towards the bright-blue sky, as if trying to merge with it.
