Plants & Growing

Delphinium Care & Growing Tips In The UK

Delphiniums growing naturally in the wild

Delphinium, often called Larkspur, is a perennial plant bearing clusters of richly-hued flowers. It is native to the Northern Hemisphere and is found in many settings, ranging from hilly meadows to well-tended flower beds. This beautiful ornamental flower is not only fairly easy to grow, it brings both eye-catching colour and uncommon grace to a garden.

Not to be Deistic but the Delphinium was self-evidently assigned to one of the Grand Designer’s master sculptors, for – unlike many another plant – the Delphinium is a work of art that is finely balanced in all its elements, each of which is in harmony with the others, and with the whole being lovelier than the sum of its parts.

The Delphinium plant comprises a stem or ‘spike’ varying in length from about ten centimetres to over two metres, depending on the species. It has palmate leaves with well-defined lobes that are often pointed. Even here one gets variety: depending on the species each leaf has from three to seven lobes. Crowning the plant is a raceme of brilliantly-coloured flowers, closely clustered.

In nature, the colours range from light blue to deep purple, making the Delphinium one of the few flowers to occur naturally in true tones of blue. Less common species and hybrids and cultivars come in many other colours including white, yellows and reds.

Close up of a blue delphinium flower
Close-up, Delphinium flowers look even more beautiful

In the vast majority of species, the flower, as we see it, comprises not only of the petals proper but also the (coloured) sepals.  Five sepals – usually mistaken for petals – fan out within which four much smaller petals are set. The top sepal projects a rearward spur as if to defend the pretty flower. In many varieties, right in the centre of this delicate assembly is a decorative eye or ‘bee’ – a floral ‘beauty spot’.

The distinctively-shaped bud reputedly gave the plant its name: the bud reminds one of a dolphin’s head and the top petal’s trailing spur resembles a fish’s body, leading the Hellenes to christen the plant after the Greek word for dolphin – delphíni.

Delphinium varieties have striking and appealing names; take Magic Fountain (in various hues), Blue Lace and Red Caroline, Faust and Galahad, Sungleam and Summer Clouds, and Blushing Bride with . . . a Million-Dollar Blush! Yet as striking and appealing as such names are, the names’ possessors are even more so. Stately and upright but swaying or even willowy in a breeze, and with a gamut of brilliant reds, purples, or blues colouring the floral crown, Delphiniums make the ideal backdrop to a garden. In fact, this beautiful plant can be made the centrepiece of a garden.

Types of Delphinium

A genus within the Ranunculaceae Family, Delphinium is the family’s second-largest species numbering over 300 varieties. They range from two feet to six feet in height.

Originally a wildflower, Delphiniums have been cultivated and hybridised for garden and ornamental purposes.

A floral composition of Delphiniums
Florists will often make good use of Delphiniums!

These cultivars and hybrids have been developed for garden, ornamental and floristry purposes, hence the diversity in size and colour, and even in other attributes such as tolerance to climate and resistance to pests. For instance, while the Dwarf Blue Mirror grows only up to fourteen inches and has a deep blue colour, the Moonbeam is often six feet tall and bears pure white blossoms.

Notable and popular varieties include the Magic Fountain series, Belladonna variants, and the Pacific Giants, which are among the tallest varieties – maxing out at seven feet and found in an abundance of hues including white and pink. Belladonna includes Bellamosum and Cliveden Beauty, both of which produce intense blue blooms.

The Magic Fountain series is known for relatively denser floral clusters. Producing flowers in white, blues, and purples, the white variant draws particular mention: snowy white sepals and petals adorned with big, near-black eyes, the simple colour combination and eye-catching contrast make for a particularly arresting Delphinium.

Among the Pacific Giant series is Galahad, which is notable for producing all-white flowers. This popular variety is a member of the Round Table strain which also includes King Arthur, Guinevere, and Black Knight.

At the other end of the scale from the Pacific Giants are Chinese Delphiniums which grow to between one foot and two feet, as reflected in their names which include words like dwarf and pygmy. Curiously, they produce a largeish flower and, therefore, have the scientific name Delphinium Grandiflorum!

Varieties that produce flowers of unusual or rare colours include Summer Morning, a Chinese Delphinium with pink flowers, and Delphinium Semibarbatum or Delphinium Zalil which bears a solid yellow flower.

Horticulturists constantly cultivate and cross-breed Delphiniums and even use tissue culture and other more advanced techniques. As a result of their efforts, gardeners and florists are rewarded on a periodic basis with varieties that have some new feature like altered floral shape or density, or more intense hues in certain colours, such as crimson.

Delphinium is a perennial plant but in regions that do not have a proper winter season, the plant does not become dormant. Instead, it continues to bloom twice or thrice per season and becomes a biennial, as in California.

Delphinium often has descriptors like royal, regal, aristocratic, and monarch applied to it, and for good reason. The plants are tall and erect, even graceful. The flowers, especially of the giant varieties, ‘look down’ on the more ‘common’ denizens of the garden. Add the fact that the most common colours are ‘royal’ blue and ‘royal’ purple, and it is but natural to conceive of the Delphinium as the floral monarchy.

Feeding, Care & Growing Tips

Delphinium plants should be watered moderately three to four times per week. Watering should be at soil level. Avoid watering from above the plant to minimise the possibility of powdery mildew or even stem rot or crown rot from setting in. Make sure that the water drains well as Delphiniums have a very low tolerance for waterlogged soil.

About once a month sprinkle some 10-10-10 or all-purpose fertilizer around the stalk but do not push it into the soil. For English Delphinium varieties, use 12-12-12 fertilizer.

Periodically mulch the plant during the flowering season by spreading a small amount of the plant’s own mulch at the base of each plant. After autumn comes around and the flowers die, apply several inches of a heavier mulch at the roots. At the end of winter, remember to clean out the mulch shortly before you expect spring frost otherwise there is a risk of stem rot.

The Delphinium’s many species and types and the various zones they can be grown in make for a quite combination of factors; thus, there is no ‘one size fits all’ type of prescription.

Any care and growing tips recommendations should be taken as guidelines and the gardener should be encouraged to experiment within reasonable bounds. For example, given the Delphinium type and the conditions (soil and zone), nutrients like wood ash or bone meal in varying quantities can be mixed into the soil in spring.

Excluding dwarf varieties, mature Delphiniums benefit from staking. Try to stake them in mid-April. The length of the stakes should be nearly as much as the particular delphinium in question. The stakes should enclose the plant’s stem and not the floral stalk. Use four stakes to form a square around the stem and apply two or three ties. The front two stakes may be shorter than the rear ones so as not to detract from the beauty of the plant and to allow some movement to the stem in a breeze.

You can multiply your Delphinium plants (or oblige your neighbours!) by selectively cutting stalks when they are shoots so as to plant and root them.

While some Delphinium varieties attract aphids, mites and leaf miners, the most common and main threat to this plant is from snails and slugs. You can deter these pests, particularly when they are most vulnerable during winter dormancy, by pouring a 1:60 solution of Aluminium Sulphate all around the crown. In the growing season, you can sprinkle red cayenne pepper on fresh young growth. Finally, you could try methiocarb pellets but be aware that these are also toxic to pets.

On the plus side, Delphinium is a magnet not only for slugs but for hummingbirds – and a repellent to deer and rabbits!

Habitat & Growing Conditions

The best type of soil for Delphinium is deep, loamy, and limey soil tending to the alkaline, though many types will grow perfectly well in neutral or acidic soils too. Adding compost to even good soil will improve results by effecting richer, more intense, blooms. If the soil’s pH is on the low side, some lime may be added to it. Most critically, the soil must have very good drainage as undrained or even poorly-drained soil will cause root rot.

The plant should get about seven hours of exposure to the sun. Originally a native of hilly regions and climes, the Delphinium does best in relatively open spaces that are not very close to trees or solid man-made structures. Blustery sites are also unsuitable for Delphiniums; however, gentle breezes that cause it to sway not only pose any danger, but they will also enhance the beauty of this ornamental plant.

Light purple and pink delphiniums growing naturally in a field
Beautiful petals that can be used for wedding confetti

The Delphinium thrives in cool and moist climates that drop to near freezing in the winter. Recommended hardiness zones are 3 through 7. You can grow certain Delphinium species in zones 2 and 8 too, though with different degrees of success. In zones 7 and 8 Delphiniums should be sheltered from the hot midday sun. Hardiness zones, also called planting zones, were devised by the USDA (United States Dairy Association) so as to demarcate geographical regions by climactic patterns – helping to identify which plants would or would not survive through a typical winter in a particular region.

When transplanting Delphiniums, the root-ball should be just underneath the soil level. Pack the plant tightly into the soil to ensure that no air-pockets exist around the roots, and water it in generously. Delphinium plants should be spaced two or more feet apart.

Pruning Delphinium

Trimming and thinning are very important for a Delphinium plant’s beauty and well-being.

After the plant’s first flowering of the season and just before summer, trim most or all of the flower stalks – but not the rest of the crown – in between the lower-most flower and ground level. This gardener’s trick will probably cause the plant to bloom once again in late summer or early autumn.

Cut spent flower spikes down nearly to the ground or to the level of any emerging side shoots. This practice is called commonly known as ‘deadheading’ by gardeners.

Annual thinning is of utmost importance as uncontrolled blooming may well cause the plant, especially cultivars and hybrids, to self-destruct. Thin the shoots when they are four inches tall. Leave two spikes for a one-year plant, three for a two-year plant, and so forth. You can have five to seven spikes on mature plants and over 20 on eight-plus-year plants. As for the plant’s stalks, every three or four years these can be dug up, divided into separate clumps and re-planted.

After the plant’s first frost, cut the stems down to ground level. Some gardeners do so every year and, depending on the zone, climate, and type of Delphinium, this is good practice.

Delphinium is toxic to mammals if ingested. It is a frequent cause of grazing cattle being poisoned in the American Mid-West. If you are a cat or dog-owner do not leave any cuttings – flowers or otherwise – where your pets can get at them.

Where To Buy Delphinium

Delphiniums are widely available. You can buy potted Delphiniums from a nursery or even online for delivery by mail. Nurseries and also mail order companies specialise in different species, hybrids, and cultivars so if the particular type you are looking for is not available at one nursery or mail order store, be sure to try another one. Buying potted young cuttings, as opposed to seeding Delphiniums, gives you a head start in growing them without the trouble associated with germinating them from seed.

Delphiniums can be grown from seeds. However, unlike many plants, Delphinium seeds start losing viability quite soon, from one to two years. Seeds germinate best when planted in early spring or autumn, though they can be planted year-round. Do not plant seeds of cultivars and most hybrids directly into a flower bed but plant them in pots or flats indoors. On the other hand, you could also look to plant the seeds of naturally-occurring Delphiniums directly into a prepared flower bed.

Or, you could try to borrow a stem for rooting from your neighbour!

About the author

Kersasp 'Kersie' Shekhdar

Kersie learnt the basics of gardening as a toddler, courtesy of his grandfather. In his youth he was an active gardener with a preference for flowering plants. He is a professional and vocational writer and his freelance projects have spanned various kinds of writing.

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