How to grow delphiniums, the kings of the cottage garden

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.

Because of the long spurs on its flowers, the word delphinium derives from the Greek delphis, meaning dolphin. This seems fitting, since the only other blue that rivals the piercing tones of delphiniums is the sea when it glows in incredible shades of aqua and lapis in the sun.

The blue Elatum hybrids that stop you in your tracks by blooming in Côte D’Azur tones of cerulean and cobalt include ‘Blue Nile’ (ultramarine), ‘Skyline’ (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 sizzling 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 differ from the spire-forming Elatums, having widely spaced blooms on branching stems.

Yes, most forms are perennial, blooming year after year. But there is a good range of easy short-lived forms, including annuals, biennials, and short-lived perennials, many of which provide for long-tongued bees and make fabulous cut flowers. They tend to have more widely spaced blooms than the classic delph spires of chocolate-box cottage gardens, but this arguably lends them more to the contemporary naturalistic planting style. They include Delphinium grandiflorum and true larkspurs (Consolida). ‘Summer Nights’ is a piercing blue; ‘Blue Cloud’ has an airy habit; and ‘Blue Butterfly’ is low-growing. Special Plants nursery offers a range of interesting forms, including the orchid-like mauve-silver biennial D. requienii, which self-sows.

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. They enjoy elbow room and being bathed in sunshine, so don’t squeeze them in amongst a crowd of plants or behind portly plants. Since their tall stems are hollow, a windy site is best avoided.

Once the plants surge into growth, supports are vital to prevent the tall stems snapping and keep the plant upright – these can be manmade stakes or simply four bamboo canes or hazel sticks bound with twine.

Yes – feed and water regularly during the growing season, especially in periods of drought and heat.

Delphs can be grown successfully in pots. Ensure the pot has drainage holes and place pieces of broken pot in the base to boost drainage; you could also sit the container on pot feet. Use a loam-based compost, mixed with grit. Finally, dress the top with a dense layer of grit or sharp gravel to put slugs and snails off.

Short-lived delphiniums or larkspurs are usually raised from seed. The annuals can be started under cover in September (to plant out the following spring) or under cover in March or April (to plant out in May or June).

Being toxic plants, wear gloves to handle delphiniums and plant them at the back of the border, away from pets.

Delphiniums are prone to powdery mildew, but providing some air flow and elbow room will help to prevent it.

What’s eating my delphiniums?

The main pests for delphiniums are slugs and snails, who seem to 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.

Delphinium 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, we must relentlessly protect the classic border delphs from gastropods. But it is worth it at the height of summer, when you can sit back and gaze at a mass of bright-blue delphiniums soaring towards the bright-blue sky, as if trying to merge with it.