Delphiniums - The Aristocrats Of The Herbaceous Border
If ever there were a plant that combined cathedral spire, overachieving peacock and slightly temperamental Victorian aristocrat, it would be the Delphinium. The aristocrats of the herbaceous border. Tall, dramatic, faintly judgemental and always dressed in shades of blue that make the summer sky look like it’s not really trying.
If you have a garden and you’ve never grown a Delphinium, you’ve either shown remarkable restraint or you’re still recovering from the last time one flopped face-first into your roses during a mild breeze. Because let’s be honest: Delphiniums are not low-maintenance background plants. They are headline acts. They require planning, feeding, staking, vigilance and occasionally a very stiff drink (for you, not them).
But when you get them right? There is nothing quite like them.
So let’s get properly into the guts of growing Delphiniums - the types, the science, the soil obsession, the propagation wizardry, and how to keep them upright long enough to admire.
Welcome to the world of growing Delphiniums.
Oh and Yes before anyone says anything - its an herbaceous border because I'm old school and I don't care 😉....
What Exactly Is a Delphinium?
They belong to the buttercup family, Ranunculaceae, which should immediately tell you two things: they’re related to other cottage garden divas like Hellebores and Aconites, and they contain toxic compounds. So best not to eat them.
The name “Delphinium” comes from the Greek delphis, meaning dolphin. The flower buds apparently resemble a dolphin.
The classic garden Delphiniums are usually hybrids known as Delphinium x elatum. These are the tall ones, spire-forming types that dominate traditional British borders that can easily reach 1.5–2 metres in good conditions. They die back completely in winter and re-emerge in spring from a crown at soil level. There are also shorter types derived from Delphinium grandiflorum, which are more compact and slightly less inclined to reenact scenes from “Gone with the Wind” at the first gust of wind.
Types of Delphinium You’ll Meet in the UK
The Elatum Group is the big one - literally. These are the tall border Delphiniums with densely packed flower spikes. Colours range from deep royal blues and indigos to lilac, pink and pure white. Many have a contrasting “bee” in the centre of each flower (that little eye that looks like it’s judging your staking technique). Popular series include the Pacific Giants, the New Millennium series and the more recent compact but sturdy varieties bred for improved disease resistance.
The Pacific Giants are often sold as seed mixes and can be enormous. They produce massive flower spikes in mixed shades of blue, lavender, pink and white. Spectacular, but sometimes structurally optimistic. Although they are glorious, they are often short-lived (2-3yreas) - think “live fast, flower hard, die young”.
The Magic Fountain series are Shorter (around 90–120 cm), better suited to smaller gardens or windier sites. More manageable but still impressive. Sometimes called the Guardian series.
Then there are the Belladonna types. These are more branched and airy, with looser flower spikes and generally better repeat flowering. They’re often a bit shorter and more forgiving. If Elatums are opera singers, Belladonnas are talented jazz musicians- still impressive, but less likely to demand silk gloves.
Finally, the smaller Delphinium grandiflorum types are compact, bushy and ideal for the front of borders or containers. They don’t produce the towering spires, but they compensate with intense, electric-blue flowers that look like someone turned the saturation up too far.
The Perfect Spot: Sun, Soil and Shelter
They need a minimum of six hours of sun a day. Less than that and they will stretch, flop and sulk. A south or west facing border is ideal. In Scotland or the north of England, full sun is rarely a problem, but in the south, they’ll still appreciate plenty of light but won’t mind a little afternoon shade if the summer is particularly fierce (by British standards, which is to say “two days above 28°C”).
Soil is where you earn your stripes. Delphiniums are greedy. They like fertile, well-drained but moisture-retentive soil. Heavy clay can work if improved with generous amounts of compost or well-rotted manure. Sandy soil needs organic matter to stop it drying out. Think of Delphiniums as elite athletes: they want rich food, regular drinks and a stable environment.
Delphiniums resent sitting in cold, waterlogged soil so good drainage is essential not a suggestion. Crown rot can wipe out a mature plant faster than a January cold snap. If your soil turns into a bog in January, consider raised beds or incorporating grit.
Wind is the eternal enemy. Those glorious flower spikes are basically sails. An exposed, windy site will lead to heartbreak. Plant them where they are sheltered by fences, hedges or other sturdy plants. And stake them. Always stake them. More on that later.
Planting Delphiniums
Dig a generous hole, incorporate plenty of compost or well-rotted manure, and ensure the crown sits just at soil level -, not buried too deeply otherwise it'll rot. Water in thoroughly.
Spacing depends on variety, but allow around 45–60 cm between plants for tall types. They need airflow to reduce disease, particularly mildew.
After planting, mulch around the base with compost. This helps retain moisture and suppress weeds, both of which your delphiniums will appreciate enormously.
Feeding and Watering
If Delphiniums had a motto, it would be: “Have you fed me recently?”
In spring, as growth begins, apply a balanced fertiliser such as Growmore. Once flower spikes start forming, switch to a high-potash feed (like tomato fertiliser) every couple of weeks. This supports strong stems and abundant flowering.
Water regularly during dry spells. In the UK, that usually means being vigilant from late May through August. Consistent moisture is key; erratic watering can stress plants and encourage mildew.
Staking: The Non-Negotiable Ritual
Let’s talk about staking. It is not optional.As soon as new shoots reach about 30 cm tall, insert sturdy canes around the clump. Use soft twine or plant ties to gently secure the stems. Do this early. Waiting until the spikes are fully grown is like fitting scaffolding after the building collapses.
Some gardeners use ring supports, pea sticks or even discreet metal frames. Whatever your method, aim to support the stems before they lean.
Flowering and Deadheading
In the northern hemisphere Delphiniums usually flower from June into July and even August if the weather is right. The first flush is the most spectacular. Tall spires packed with flowers open from the bottom upwards, creating weeks of colour.
To encourage a second, smaller flush, cut back the spent flower spike down to a lower set of leaves once flowering has finished. If you do this promptly and keep feeding and watering, you’ll often get a second show in late summer.
After the final flowering, allow foliage to remain until it naturally dies back in autumn. Then cut down to ground level and mulch lightly for winter protection.
Common Problems (Because Of Course There Are)
Slugs and snails consider Delphiniums a five-star buffet, especially in spring. Young shoots are particularly vulnerable. Use barriers, pellets, beer traps or night-time patrols with a torch and a sense of vengeance.
Powdery mildew can be an issue in dry summers, especially if plants are stressed. Good spacing, regular watering and decent airflow help enormously.
Crown rot can occur in poorly drained soils. This is why drainage and not burying the crown are so important.
And occasionally, a seemingly healthy Delphinium will just give up after a couple of years. They are not the longest-lived perennials. Many gardeners treat them as short-lived perennials and replace or divide regularly.
Propagation: Making More (Because One Is Never Enough)
Growing from seed is economical and exciting, especially with named series like Pacific Giants. Sow indoors in late winter (February to March) in a propagator or on a bright windowsill at around 15–18°C. Lightly cover the seed and keep moist. Germination usually takes 2–3 weeks.
Be aware that seed-grown plants may not come true to type unless they’re from a stable series. You might get subtle differences in colour or height. This is not a tragedy. It is botanical suspense.
Division is best done in early spring as new growth appears. Lift the clump carefully and split it into sections, each with roots and shoots attached. Replant immediately. Not all Delphiniums divide well, particularly older woody crowns, but younger plants respond better.
Basal cuttings are arguably the gold standard for maintaining named varieties. In spring, when shoots are about 7–10 cm tall, gently pull or cut them away from the base with a sliver of root tissue attached. Insert into gritty compost, keep moist and warm, and they will root within a few weeks. It feels faintly magical, like cloning your favourite plant.
Winter Care
In very wet regions, ensure drainage remains good over winter. If necessary, improve soil around plants or consider planting on slight mounds.
Delphiniums in the Border
Design-wise, Delphiniums are classic back-of-the-border plants. Their height makes them perfect for the rear of a mixed border, where they can tower behind Roses, Peonies and hardy Geraniums.
They pair beautifully with soft pinks, whites and silvers. The combination of deep blue Delphiniums and pale pink Roses is a cottage garden cliché for a reason. It works.
Shorter varieties can be used mid-border or even in large containers, provided feeding and watering are consistent.
So why bother
They are dramatic. They are demanding. They are occasionally exasperating. But they are also, without question, one of the most spectacular perennials you can grow in the garden.
And frankly, if you can keep a Delphinium upright through a windy July, you can probably handle anything the gardening world throws at you.
Now go buy some canes. You’re going to need them.
Happy Delphinium growing.
If you have any questions please ask.
Geoff.
Who am I?
I'm a horticulturalist with over 40 years experience in the field. From running garden centres and nurseries growing plants for sale to now, well for the last 12 years, running my own gardening business I'm bringing my expertise to those who are interested. I receive no money or reward for my blogs so they're purely my own thoughts, ideas and experience - enjoy.
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