Each year the National Garden Bureau declares a “year of” that features four plants: one vegetable, one perennial, one annual, and for the first time in 2016, one bulb. We looked at the Year of the Carrot and the Year of the Begonia last month. Now let’s look at this year’s perennial, the delphinium. In coming weeks, I’ll look into the last winner.
The genus Delphinium includes about 300 species of perennials, biennials and annuals, with different species being found throughout Eurasia and North America. The genus is in the Ranunculaceae family (buttercup family) and is very close to the monkshoods (Aconitum spp.), with which delphiniums share very deeply cut palmate leaves and a similar range of colors. Unlike monkshoods, though, delphiniums have an open flower with a nectar-filled spur behind it.
The Greeks felt the oblong flower bud with its extended spur looked like a dolphin, Delphis, hence the name Delphinium, which means little dolphin. They are also sometimes called larkspurs, because the foot of a lark has a similar spur. That said, many gardeners prefer to distinguish between the perennial Delphinium and the closely related annual, Consolida, by calling the former delphiniums and the latter larkspurs. Whatever the name, though, butterflies and bees love to sip the nectar contained in the flower’s spur.
Although various delphiniums were known since ancient times, it was not until the late 19th century that the delphinium began its “career” as an ornamental plant. The French breeder Victor Lemoine crossed then the European species D. elatum with other species like D. formosum, D. bruninianum and D. cheilanthum to create what is now usually simply called “the delphinium” (D. x elatum or sometimes D. x cultorum), although it may also be called “hybrid delphinium” to distinguish it from other species. The plant was originally developed as a greenhouse cut flower and that shows: the flower stalks don’t stand up well to outdoor conditions and will often snap off if they are not staked. This wasn’t necessary in a windless greenhouse, but outdoors, that’s a different story! Despite this flaw, the delphinium quickly became a classic element of the English style flower border in the 1890s and it is still used that way today.
The usual color of wild delphinium flowers is blue or purple, rarely white, although there are some species with red or even yellow flowers. It was by crossing a red-flowered species, D. cardinale, with classic hybrid delphiniums that the range of pink-flowered delphiniums we know today was born.
Hybrid delphinium flowers can be simple, semi-double or double, often with contrasting white or black eye called a “bee”.
More than 100 years after it was first introduced, the hybrid delphinium (D. x elatum) still dominates the delphinium market… and it is certainly a spectacular plant, forming a dense mass of basal leaves from which emerge upright unbranching spikes of dense flowers. They can grow up to 8 feet (2,5 m) high, although 4 to 6 feet (120 to 180 cm) is more typical.
The most popular strain remains the Pacific Giants, developed by American hybridizer Frank Reinelt in the mid-20th century. Some cultivars are named for characters from the legend of Camelot, such as ‘Black Knight’ (very dark purple, black eye), ‘Guinevere’ (lavender pink, white eye) and ‘King Arthur’ (dark purple, white eye) and others for birds such as ‘Blue Bird’ (medium blue, white eye) and ‘Blue Jay’ (medium blue, dark eye).
Today, however, they have competition: the New Millennium series (also called New Zealand Hybrids), developed by the New Zealand breeder Terry Dowdeswell, is more recent, but has become the favorite strain of delphinium enthusiasts. These plants bear denser and larger flowers, have a much more solid stem, better disease resistance and a longer life. They can be obtained as a mixture, such as ‘New Millenium Stars’ (all colors, both singles and doubles, 3 to 6 ft/90 to 180 cm) or ‘New Millenium Pagan Purples’ (shades of purple, double flowers, 4 to 6 ft/120 to 180 cm) or individual cultivars, such as ‘Blue Lace’ (sky blue with a lavender accent, double, 5 to 6 ft/150 to 180 cm)) or ‘Sunny Skies’ (blue, white eye, single flower, 4 to 6 ft/120 to 180 cm)).
And there are also dwarf delphiniums, including the series ‘Magic Fountains’, which offers a pretty good selection of colors on plants of only 30 to 36 inches (60-90 cm) high that don’t need staking.
The hybrid delphinium is often short-lived, especially in climates with hot summers. In fact, in many climates, it is often grown as an annual! But it can easily live 5 or 6 years or even more in areas with cool summers, as in Great Britain, Northern and Atlantic Canada and Scandinavia. In my area, Quebec City, for example it thrives and lives on and on, yet in Montreal, only a few hours drive away, it rarely lasts more than 3 years. But then, Quebec City has cool summers and Montreal, hot ones and that makes all the difference.
Flowering takes place in early summer and lasts 3 or 4 weeks. You can force the plant to bloom again in the fall by cutting it back nearly to the ground after the first flowers fade, but this second flowering is not reliable and is also far less spectacular than the first, notably since it is much shorter.
Finally, if hybrid delphiniums are sometimes short-lived, it’s certainly not because they can’t tolerate cold winters: they are solidly hardy to zone 3 and worth a test in zone 2!
This species (D. grandiflorum, formerly D. chinensis) is also fairly common in garden centers. It does not produce the tall densely-packed flower spikes of its more popular cousin, but rather many shorter, more abundantly-branched stems with more scattered flowers. Its leaves are deeply cut, like carrot leaves. Moreover, it blooms all summer from late June to September.
On the down side, this species truly is short-lived, in all conditions. Most gardeners will find it behaves like a biennial, producing leaves only the first year and flowers the second, then dying, so if you buy it as a plant in the spring, you might as well consider it an annual. However, it will maintain itself through self-sowing when conditions are right. Just don’t cut it back after it blooms, as that will keep it from self-sowing.
No staking is needed for this species, as it reaches only 1 foot (30 cm) high for dwarf varieties) and about 2 feet (60 cm) for standard ones. The flowers are usually in various shades of intense blue, but there are a few cultivars with white or pale pink flowers.
Finally, it too is a very hardy plant, to zone 3.
Yes, there are annual delphiniums, that is in the genus Delphinium, but few are grown. However, as mentioned above, the related genus, Consolida*, usually called larkspur, is often confused with true delphiniums. C. ajacis and C. regalis are usually are sown outdoors in the fall for bloom the following summer.
*If I mention Consolida at all, it’s because many taxonomists believe it should be moved to the genus Delphinium and in fact, some sources already list it that way.
Delphiniums are pretty but are poisonous in all their parts. Don’t eat them and wash your hands after pruning them.
Plant delphiniums in full sun or partial shade (they prefer partial shade in hot summer climates) in well drained soil rich in organic matter and a bit on the moist side. It can be slightly acid to slightly alkaline. Supply the plants’ mineral needs with an annual application of compost or use a slow-release organic fertilizer. Avoid fertilizers rich in nitrogen (the first number), because they stimulate extra tall flower spikes that are more likely to snap.
Staking is important for the taller strains of hybrid delphinium, as they are not wind resistant. This can be as simple as planting them among medium-sized shrubs (my method and it works very well) or using extra-tall peony rings (about 3 feet/90 cm high). Just place the latter directly over the plant early in the season so its stalks grow right through the ring and they will be firmly supported. Or use other garden stakes (bamboo is particularly discrete), as you choose. Better yet, plant varieties known for their wind resistance!
Unlike most perennials, delphiniums are almost never multiplied by cuttings, division or tissue culture (although all those techniques are possible), but is instead grown from seeds. Even nursery-grown plants are started from seed. That is why even strains with cultivar names like ‘Black Knight’ or ‘Sunny Skies’ still show some variability in flower color, height, foliage color, etc.: seed-grown plants are never 100% identical.
Since even plant nurseries grow their delphiniums from seed, why not grow your own that way? It is relatively easy to do and of course you’ll save a lot of money, as seed packs usually include 30 to 50 seeds: that’s a lot of delphinium bang for your buck!
Sow seeds in early to mid March in a pot of moist sterile potting soil, barely covering the seeds. Seal the pot inside a plastic bag and place in the fridge for 14 days, then expose it to normal indoor heat and moderate light. In no time, you’ll have a host of small seedlings. When true leaves appear, remove the bag and, once spring is well-established, start acclimating the seedlings to outdoor conditions. Plant them out when there is no more danger of frost, where you want them to bloom: they’ll flower the following year. Greenhouse growers successfully cultivate their delphiniums in such a way that they bloom the first year from sowing, but this is unlikely under the growing conditions of the average home.
Alternatively, you can also sow the seeds directly outdoors in July in an out-of-the-way corner of the garden, transplanting the seedlings to their final position in October and that will give you a beautiful flowering plant the following season. Or sow them in the autumn, in which case they will germinate the following spring, giving their first flowers only in the third year.
Here are a few delphinium seeds sources:
Pests and Diseases
Delphiniums have more than their share of potential diseases, including powdery mildew, downy mildew and leaf spots. You can generally avoid powdery mildew by keeping the soil a bit moister in times of drought. To avoid downy mildew and leaf spots, first choose a variety recognized for its disease resistance, then plant it in a well-ventilated spot.
As for pests, slugs are the bane of delphinium growers: they seem to find fresh spring foliage particularly delicious. A bit of hand-picking early in the season can be helpful or try slug pellets based on iron phosphate. As the leaves toughen up, the slugs will move on to other plants.
So there you go: a beautiful yet somewhat temperamental plant (especially in areas with hot summers) but still one well worth trying. Why not grow a few delphinums during this, the “Year of Delphinium”?
For more on growing delphiniums, visit How to Grow Delphinium.