Delphiniums are among the most majestic and visually commanding flowering plants in the temperate garden, belonging to the genus Delphinium within the family Ranunculaceae — the buttercup family. The genus contains more than 300 species, native primarily to the mountainous regions of the Northern Hemisphere, with significant diversity across Europe, Asia, and North America, as well as a number of species found in the high mountains of tropical Africa. The common name “delphinium” derives from the Greek word delphis, meaning dolphin, a reference to the shape of the unopened flower bud, which was thought to resemble the nose of a dolphin. They have been cultivated in formal gardens since the 16th century and remain one of the most cherished of all classic cottage garden plants.
The flowers of the delphinium are its defining glory. They are produced in tall, densely packed vertical spikes — called racemes — that can reach anywhere from 60 cm in compact dwarf varieties to an extraordinary 2 metres or more in the towering Pacific Giant hybrids. Each individual floret is delicate and intricate, featuring a distinctive spur at the back and a central cluster of smaller petals called a “bee” — often contrasting in colour with the outer petals. The colour range is dominated by the cool end of the spectrum — blues, purples, lavenders, and violets — in shades that are among the most vivid and saturated of any flowering plant. White, cream, and pink cultivars also exist, and bi-colour combinations are common.
There are several main groupings of delphiniums that gardeners work with. The tall Elatum Group hybrids — the classic English border delphiniums — are the most spectacular, producing enormous flower spikes in a stately range of blues and purples. The Belladonna Group produces looser, more branching flower stems and a slightly more informal appearance. The Pacific Giants are vigorous American-bred hybrids bred specifically for their extraordinary height and densely packed flower spikes. The Grandiflorum or Chinese delphiniums are smaller, more delicate plants bearing loosely arranged flowers over a long season, and are better suited to containers and the front of borders.
Delphiniums are cool-season perennials that perform best in climates with mild summers, cool nights, and cold winters. They thrive in full sun with shelter from strong winds — their tall, top-heavy spikes are highly vulnerable to wind damage — and require deep, rich, fertile soil with excellent drainage. They are heavy feeders and respond very well to generous incorporation of organic matter and regular liquid feeding throughout the growing season. After their main flush of flowers in early summer, cutting the spent spikes back to the base will often encourage a second, smaller flush of blooms in late summer or early autumn, extending the season of interest considerably.
Despite their breathtaking beauty, delphiniums come with an important caution — all parts of the plant are toxic to humans and animals if ingested, containing alkaloids called diterpenoid alkaloids that can cause serious illness. Livestock, particularly cattle and horses, are especially vulnerable, and care should be taken when growing delphiniums on properties where animals have access to garden areas. Gardeners should wear gloves when handling the plants, particularly when cutting stems or dividing roots, as the sap can cause skin irritation in sensitive individuals. With sensible precautions, however, delphiniums pose no practical danger in a normal garden setting.
In garden design, delphiniums are indispensable in the classic English cottage garden and the formal herbaceous border, where their towering vertical spikes provide height, structure, and an unmatched depth and richness of colour. They are most effective when planted in bold groups of three or more, where the massed vertical spikes create a spectacular backdrop for mid-height and low-growing companions such as roses, peonies, geraniums, and achilleas. As cut flowers, delphiniums are outstanding — their long stems, vivid colours, and impressive presence make them a favourite in large floral arrangements and wedding flowers. Whether grown in a grand country garden border or in generous containers on a city terrace, delphiniums reward the effort invested in their cultivation with a floral display of almost unparalleled majesty.
How to Grow Delphinium from Seed
1. Growing delphiniums from seed is one of the most rewarding routes to establishing these magnificent plants, and it is considerably more economical than purchasing established plants — particularly when you wish to grow them in the large groups that show them off to best advantage. The key challenge with delphinium seed is that it is short-lived and loses viability rapidly, so freshness is critically important. Always purchase seed from a reputable supplier with good stock turnover, sow as soon as possible after purchase, and store any unused seed in a sealed container in the refrigerator rather than at room temperature.
2. Choose the right time to sow. Delphiniums can be sown at two main times of year with good results. The most common approach is to sow indoors in late winter to early spring — January to March in the Northern Hemisphere — for plants that will flower in their first summer. Alternatively, seeds can be sown in midsummer for overwintered young plants that will flower particularly strongly the following year. Both approaches work well, though the midsummer sowing often produces the most vigorous first-year plants.
3. Chill the seeds before sowing to significantly improve germination rates. Delphinium seeds germinate most reliably when they have been exposed to a period of cold, mimicking the natural winter conditions they would experience outdoors. Place the seeds in a small sealed plastic bag with a pinch of barely moist vermiculite or peat and refrigerate them for one to two weeks before sowing. This cold stratification process breaks dormancy and can dramatically increase the percentage of seeds that germinate.
4. Keep seeds away from heat during germination. Unlike many flower seeds that require warmth to sprout, delphinium seeds actually prefer cool conditions and will germinate most reliably at temperatures between 10 and 15°C (50–60°F). High temperatures — anything above 20°C (68°F) — can trigger dormancy and prevent germination entirely. This is one of the most important and frequently overlooked aspects of growing delphiniums from seed successfully.
5. Use a fine, sterile seed-starting mix for sowing. Fill small pots, seed trays, or individual cells with a moist, light, well-draining seed-starting medium. Avoid heavy or dense potting composts, which can compact around the tiny seeds and impede emergence. A blend of seed-starting mix with a small addition of fine perlite provides an ideal combination of moisture retention and drainage for delphinium seeds.
6. Sow seeds thinly on the surface of the moist growing medium and cover them with a very thin layer — approximately 2 to 3 mm — of fine vermiculite or sieved seed-starting mix. Delphinium seeds need darkness to germinate, unlike many other flower seeds that require light, so this thin covering is important. Do not sow too deeply, however, as the seedlings are small and fragile and must not have too far to push through the medium to reach the surface.
7. Cover the trays with dark paper, cardboard, or an opaque cover to exclude light during germination. Check the trays daily by lifting the cover briefly to look for emerging shoots. As soon as the first seedlings appear — which may be as early as one week after sowing under ideal conditions — remove the dark cover immediately and move the trays to a brightly lit position to prevent the seedlings from becoming etiolated in the dark.
8. Keep the growing medium consistently moist but never waterlogged during the germination period. Water from below by placing trays in a shallow dish of water and allowing the growing medium to absorb moisture upwards — this avoids disturbing the seeds or dislodging tiny seedlings that might be washed out of place by overhead watering. Remove the tray from the water dish as soon as the surface of the mix appears moist.
9. Expect germination to occur within one to three weeks under cool, dark, and moist conditions. Germination can be uneven, with some seeds sprouting earlier than others, so monitor the trays carefully over a three-week period before concluding that seeds have failed. If temperatures have been too warm during the germination period and no seedlings have appeared after three weeks, try placing the trays in a cooler location and continuing to monitor for a further week or two.
10. Provide seedlings with strong, consistent light immediately after emergence. Delphinium seedlings grow quickly and require 12 to 14 hours of bright light per day to develop into sturdy, well-branched plants. A grow light placed a few centimetres above the seedlings is ideal, or a bright south-facing windowsill kept cool and away from heating vents. Insufficient light produces the tall, weak, pale seedlings that are prone to collapse and transplant failure.
11. Thin or pot on seedlings once they have developed their first true leaves. If sown in trays, prick out individual seedlings carefully using a small dibber or pencil, holding them by a leaf rather than the fragile stem, and transplant them into individual small pots of 7 to 9 cm diameter filled with a good-quality, well-draining potting mix. Delphinium seedlings have somewhat delicate roots and must be handled with considerable care during this operation to avoid setback.
12. Begin feeding seedlings with a diluted balanced liquid fertiliser once they are established in their individual pots and growing actively. Apply at half the recommended strength every two weeks initially, increasing to full strength and weekly feeding as the plants develop further. Delphiniums are heavy feeders and respond extremely well to generous nutrition — well-fed seedlings grow noticeably faster, develop more robust stems, and ultimately produce far more impressive flower spikes than underfed plants.
13. Stake plants early, before they actually need it. Even at the seedling and young plant stage, getting into the habit of providing support is important with delphiniums. As plants grow taller, insert canes or purpose-made flower support stakes around each plant and loosely tie in the growing stems. Waiting until the stems are already leaning or have been damaged by wind before staking is far less effective and risks permanently damaging the flower spike.
14. Harden off young plants thoroughly before transplanting outdoors. Over a period of 10 to 14 days, gradually acclimatise them to outdoor conditions by placing them in a sheltered spot outside for increasing periods each day. Delphiniums are ultimately very cold-hardy plants once established, but young seedlings raised indoors in warm conditions are tender and can suffer considerable shock if moved outside too abruptly, particularly if exposed to cold winds or late frosts.
15. Transplant young plants to the garden in spring once frost risk has passed, or in early autumn if you have taken the midsummer sowing route. Prepare the planting site thoroughly by digging deeply and incorporating generous quantities of well-rotted compost or manure, as delphiniums demand rich, deeply cultivated soil to develop their extensive root systems. Choose a site in full sun with shelter from prevailing winds, and space plants at least 60 to 90 cm apart to allow for their substantial mature spread and to ensure good air circulation, which reduces the risk of powdery mildew — a common problem with delphiniums in humid conditions.
16. After the magnificent first flush of flowers in early summer, cut the spent flower spikes back hard — down to the level of the emerging basal foliage — and apply a generous liquid feed immediately afterwards. This hard cut-back, combined with feeding and adequate watering, will encourage the plant to produce a second flush of flower spikes in late summer or early autumn. At the end of the growing season, cut all stems back to the ground, apply a generous mulch of well-rotted compost over the crown, and allow the plant to rest over winter — from the second year onwards, established seed-grown delphiniums will return each spring with increasing vigour and ever more spectacular flower spikes, rewarding your initial patience and care many times over.