Delphiniums impress in the garden over summer with their striking panicles. Let us give you some tips on planting and caring for this popular bedding perennial.
Delphinium must be one of the best-known garden perennials. These blue-flowering and up to head-height plants are part of the buttercup family (Ranunculaceae) and there is estimated to be around 300 species worldwide - predominantly perennials, but some annuals and biennials. Around half are native to China, a quarter to North America and the rest to Europe and the African highlands. Wild variety Delphinium elatum is found in the Alps – one of the most important ancestors of many garden varieties, known as Delphinium elatum hybrids (Alpine Delphinium). Consolida regalis (also known as forking or branching larkspur) is also found in this region. It used to be called Delphinium consolida, but now forms its own genus. It grows at the edges of fields in lime-rich, loamy soil in full sun, and is on the red list of endangered species.
The Greek name “Delphium” comes from the shape of its flower buds, which look like dolphins. The common name “larkspur” comes from the appearance of the flower and the distinctive spur on its underside.
Since the poet Novalis described this “blue flower” so emotionally in his 1802 publication “Heinrich von Ofterdingen”, it has been a symbol of romance. It stands for unfulfilled longing, the wish for inner connection with nature and the search for inner, personal happiness. These blue flowers still exercise a magical attraction on us.
Appearance and Growth
Garden Delphiniums grow upright and can grow up to 4 or even 6 feet tall depending on the group (such as the belladonna or elatum groups). They have characteristically feathery, hand-shaped, fresh green leaves. The high, often branched panicles appear from June through to September on strong, hollow stems and bear dark to light blue, white or purple flowers depending on the variety. Some varieties even change color between blue and purple depending on the light. Newer cultivars even feature blooms in more unusual shades of pink and yellow. The flowers appear from the end of June at around the same time as many rose varieties. On the back of the individual flowers, often featuring a yellow, white or black center, is a long, slightly arched growth. This is what gives this plant its common name, as it looks like a spur.
Location and Soil
Larkspur enjoys the sun on its face but shaded feet. A flower bed in full sun but with groundcover plants is therefore ideal for Delphiniums. Larkspur loves a cool, humid environment. The soil should be sandy and loamy, rich in humus and nutrients, and the substrate slightly moist. This makes it all the more impressive that Karl Foerster, one of the most significant cultivators of larkspur, managed to grow these demanding perennials in sandy Brandenburg soil at his Potsdam nursery. He succeeded because he had plenty of composted cattle manure worked into the soil around his parent plants.
Before planting a Delphinium, it’s best to work a little compost into the soil. As larkspur is a shallow-rooting plant, you shouldn’t place the root ball too deep into the ground. When planting, leave around 24 inches between plants. Tall varieties should be supported with canes in windy locations, as the flowering stems bend easily. With a little skill, you could also build your own plant support.
During the growth period in spring, ensure good nutrient supply with compost and horn shavings. Larkspur requires regular watering in summer. During flowering, it is advisable to feed these hungry plants with liquid fertilizer every three weeks.
Larkspur hybrids will bloom a second time if you cut the stems down to one hand’s width from the ground immediately after the flowers wilt. This means they will form new, if slightly less vigorous blossoms in late summer. To support this feat, you should give the plants some fast-acting mineral fertilizer immediately after cutting them back and ensure consistent soil moisture in the following period. To ensure no water makes it into the cut, you can bend the flowering stems after cutting.
Delphinium belladonna hybrids are not very long-lived and must be dug up and separated as their vitality wanes. Elatum hybrids are less short-lived but often need rejuvenation after six years in poor soil. The plants should ideally not be returned to the same location to prevent stunted growth due to soil deterioration.
Winter protection is particularly advisable in exposed locations. If the plants are cut back to one hand’s width from the ground in fall, you can use the cut plant matter as frost protection.
With their early to high summer flowers, larkspur are the ideal companions for roses – especially when their colors are not found in roses. Their imposing flowers are sure to impress in classic cottage gardens as well as in herbaceous perennial beds. To ensure they don’t look too much like a solid mass, add these perennials individually or in groups of two to three. Delphinium are also popular cut flowers.
Tip: To dry the whole inflorescence, cut the stem before the flower opens and dry upside down in a dark place.
Important Species and Varieties
The three main cultivars are the slightly more branched belladonna hybrids, the up to 6.5 feet tall elatum hybrids and the popular medium-height Pacific hybrids. Belladonna hybrids have a slightly less dense arrangement of flowers. They grow to around 3.3 feet tall and live for three to four years. Elatum hybrids are cultivated forms of candle larkspur (Delphinium elatum), and therefore the largest species. They are nevertheless steady, and have lush, robust inflorescences with single flowers measuring up to 1.97 inches in diameter. Elatum hybrids grow without branching and are therefore very good for cut flowers. Pacific hybrids have established themselves as good plants for decorative gardens as they have particularly beautiful, large flowers (up to 2.95 inches in diameter). They generally grow to 5 feet tall and are usually harvested at two years old. Low-growing Pacific varieties are also good for container gardening.
Belladonna hybrids include the variety “Piccolo”, which has beautiful gentian blue flowers. “Moerheimli” in pure white contrasts with the dark blue, very compact “Atlantis”. “Ballkleid” is very elegant in light blue, while “Völkerfrieden” is a reliable variety in gentian blue.
Among the elatum hybrids, mildew-resistant variety “Augenweide” stands out with its two-tone flowers in light blue with dusky pink and a light center. Robust “Lanzenträger” forms flowers in gentian blue with a white center on long panicles, while compact “Polarfuchs” blooms pure white. “Overtüre” boasts a majestic combination of mid blue and pink with a black center. The New Millennium varieties are the trendsetters among the elatum hybrids. They stand out with long blossoms with dense, shapely individual flowers on strong stems. These are also frost-hardy. Good varieties include “Dusky Maidens” (dark pink with a brown center), “Misty Mauves” (purple) and “Pagan Purples” (blue-purple).
Among the Pacific hybrids, “Blue Bird” blooms in mid blue with a white center, while “Astolat” is purple-pink with a dark center. Established variety “Black Knight” has dark purple flowers with black centers and “Galahad” blooms in pure white.
Larkspur is generally propagated through separation in late summer after flowering or in spring. Even beginners should manage this with no issue. The young plants for nurseries are almost exclusively the result of meristem propagation.
Diseases and Pests
Larkspur is sadly very vulnerable to disease in hot, dry locations with poor air circulation. Powdery mildew is a particular bother to this perennial. It’s considerably easier to cultivate these plants in cool, moist coastal climates and above altitudes of 1640 feet. To prevent mildew, you should ensure regular watering. Additionally, you can spray the plants with a horsetail brew. If the infection is serious, you should remove all affected parts of the plant and dispose of these with your general household waste.
All Delphinium species and varieties are favorite snacks of slugs and snails. Protect this perennial from ending up on the menu of these pests, especially during their growth phase. Slug pellets, nightly removal and plant collars are helpful. If the leaves blacken, your Delphinium is suffering from a bacterial infection and must be removed completely.