Delphinium

DELPHINIUM

IT’S ALWAYS INTERESTING FOR A GARDENER LIKE MYSELF TO COME ACROSS A FLOWER THAT IS ESPECIALLY BEAUTIFUL 
YET EXTREMELY DIFFICULT TO GROW. THE DELPHINIUM IS THAT TYPE. I HAVE BEEN CHALLENGED FOR YEARS TO GROW THE TOWERING BLUE SPIRES THAT I FIRST SAW AT THE ROYAL HORTICULTURAL SOCIETY CHELSEA FLOWER SHOW IN LONDON, AND IN THE INCREDIBLE GARDENS OF FRANK CABOT IN QUEBEC.

I even got to see such flowers right across from my Turkey Hill garden in Westport when the proprietor of a flower farm grew some from seeds of English hybrids—they were as amazing as any I had ever laid eyes on.

I had read about delphinium and its culture in one of my favorite books, A Woman’s Hardy Garden, by Helena Rutherfurd Ely. She grew incredible flowers in Vernon, New Jersey, on her sprawling estate with the help of scores of accomplished gardeners. She warned that the plants were prone to mildew and insects, and cautioned unsuspecting readers that a dusting of wood ash from the fireplace was a good antidote. So I did everything she advised and actually, in my Middlefield garden in the Berkshire Mountains, did succeed in propagating and growing some respectable, if-not-8-feet-tall, spires of Pacific Giant hybrids. The nights of Massachusetts were still cool back then, in the 1960s and ’70s, and everything in my small gardens there grew extremely well.

Katonah is often too warm after May to grow beautiful flower spikes, and so is East Hampton. But Maine is exactly right—I grow not only delphinium like Mr. Cabot but also another hard-to-grow flower, Meconopsis, or Himalayan blue poppy, like he did at Les Quatre Vents, near the mouth of the St. Lawrence River.

He was an exemplary gardener and garden visionary, and I was lucky enough to meet him and talk with him about his ability to make Mother Nature do what he wanted her to do. His best advice: Plant what you want in as ideal an area as history or another gardener tells us. Choose showy plants that delight and astound—the blue poppy, the chanterelle mushroom, giant Astilboides tabularis, Corydalis flexuosa ‘China Blue’, Podophyllum peltatum (mayapple)—and plant them in massive quantities where they can be viewed from a good vantage point. Make walks nearby the great plantings so viewing will be seemingly “accidental but intended.”

His delphiniums were carefully placed in a sunny border where winds were staved off by a great stand of tall trees. If there were stakes supporting the spires, they were so carefully placed as to be almost invisible. And the delphiniums were more often than not the showy blue colors that we so admire and love. Of course, there are now extraordinary pinks and creams and lavenders, but I still melt when I observe a 3-foot stalk of electric-blue flowers.

I am growing nice delphiniums in my Maine garden, and Kevin and I cut them to desired lengths for arranging in the beginning of August when most of the flowers along the stems have opened. They do look nice in tall slender vases, but I still prefer them, en masse, in a mixture of shades. There are now New Zealand–bred hybrids (Delphinium x elatum, the Elatum group) that have strong stems and vigorous growth and are truly perennial. Try some of those. And good luck!

Play up the long, slender nature of the delphinium by giving it an equally tall, slender vessel like these vintage wine bottles and milk-glass soda bottles. Bicolor begonia leaves accent the ombré pattern of blues. Here, Kevin placed a few extra blossoms that were trimmed near the bottom of a stem into a shorter vessel alongside the shooting spires.

Although delphiniums look spectacular on their own, they can also add personality to a mixed arrangement of early-summer beauties. Kevin used an antique Japanese cast-iron brazier designed to resemble bamboo as an anchor for this display. He started with a floral frog, placing a cloud of hydrangea around the base, then inserted dianthus, poppies, and hollyhocks (in bud and bloom), which extended the lavender palette, and a spire of ‘Dusky Maiden’ delphinium, which elevates the grouping.

GROWING & ARRANGING

GLAMOROUS AND ARISTOCRATIC DELPHINIUM SPIRES COME IN COLORS NOT OFTEN SEEN ELSEWHERE IN THE GARDEN—MOST NOTABLY BLUES, INCLUDING ULTRAMARINE, CELESTIAL, AND IRIDESCENT EXAMPLES. THESE SPECTACULAR TALL BLOOMS THRIVE IN COOL CLIMATES AS LONG AS THEY GET PLENTY OF SUN AND CONSIDERABLE CARE.

There are very few true blue flowers in nature, so Delphinium ‘Cobalt Dreams’ stands out. 
Let the qualities that make the flower special in the garden—its height, color, and variety on the stem—be your guiding principles once you bring it inside, with arrangements that play to those strengths.

HOW TO GROW

Delphiniums can be a challenge to cultivate. Though listed in the perennial books, most are only truly perennial in their ideal climate, and are generally short-lived. With lots of sunshine and cool, moist summers, however, delphiniums can grow to staggering heights.

There are a few species groups of delphiniums. The Belladonna group includes blue or white flowers that grow 3 to 4 feet tall. You’ll find taller plants (3 to 8 feet) and more colors in the Elatum group. English hybrids reach upward of 8 feet high and boast individual double florets 3 to 4 inches in diameter. Their colors range from the rarest true blue to lilac, mauve, purple, pink, and white, with centers (called bees) that may be black, brown, fawn, white, or even striped. The Pacific Giant hybrids, developed in California by Frank Reinelt in the 1930s and ’40s, have become the industry standard, with spikes up to 9 feet tall. Originally bred to behave like annuals, they are now grown from seed-started plants.

ZONE Areas with cool, moist summers—Maine, Alaska, Oregon, or, better yet, coastal Canada—are the delphinium’s preferred places to grow. Winter is not a problem for most delphiniums. The species we grow, including the most popular strains of hybrids, are hardy to Zone 3, meaning they can survive wintertime lows as extreme as 30 degrees below zero. It’s the heat and lack of moisture that they object to—they grow best to Zone 7.

SOIL Well-drained, fertile soil with a pH that is neutral to slightly alkaline is key to success with delphiniums. When planting, prepare soil 1 foot deep with organic matter. Then use balanced fertilizer (such as 10:10:10) and a healthy mulching with rich compost to keep the roots moist. Reapply fertilizer and compost after the first blooms have been cut back (leave the foliage to grow until the later-season flower shoots begin to appear). They are heavy feeders, so add composted manure every autumn.

LIGHT Delphinium heads require full sun—six to eight hours a day—to thrive, while their roots need cool, moist shade.

CHOOSING Because delphiniums act more like biennials in many zones, gardeners must start fresh each year with new plants, which can be grown from seed or purchased in pots. Planting from seed requires patience (often yielding only foliage the first year and not flowering until the second), but is the easiest method for growing these tricky blooms. If you want a full row of beautiful blue spires, as I have in the cutting garden in Maine, buy or propagate plenty extra. If you’re buying delphinium plants from a nursery, look for healthy plants in bud. Avoid plants that have any sign of powdery mildew, fungus, insects, or yellow leaves. Don’t buy a plant that has roots running from the bottom of the pot, which indicates it has been in the pot too long and become root-bound, or pot-bound. It won’t transplant well.

PLANTING Pick a spot in the garden that is protected from the wind. These tall plants are prone to getting blown over. Dig a hole for the delphinium plant that is about 1 foot deep and twice the diameter of the container. Make sure that the top of the root-ball is level with the soil when planted. Delphiniums should be spaced 1 to 3 feet apart.

As the plants mature, all but the lowest-growing kinds (such as the dwarf forms) will require careful staking to prevent their hollow stems from snapping in the wind or rain. Stake the plants when the flower spikes are about a foot tall and continue to stake them as they grow even taller. Tie the plant to the stake at 12- to 18-inch intervals.

WATERING Ample water in the summer is essential. A dried-out delphinium root system can easily kill the plant. The soil should be moist, but without any standing water.

PRUNING Remove faded flower spikes, cutting back to the nearest secondary flower spike. After the plant’s first bloom, cut off the spent flower stalk. In the fall, when the bloom is done and the leaves have turned yellow to brown, cut the entire plant down to about an inch from the ground.

PROPAGATING You can propagate by seed, cuttings, or division. To propagate by seed, collect fresh seeds in the fall, allow to dry, and store in an airtight container. Sow indoors in midwinter in a tray or pot with vermiculite or another seed starter. The seeds do best in a cooler place (60 to 68 degrees); keep them moist and they will typically germinate in two to four weeks.

To use cuttings, take 4-inch basal cuttings in the spring. The cutting should be solid (not hollow) and the center of the stem should be white. From the side, cut shoots coming out of the plant’s crown, not the hollow flowering stems. Root the cutting in part shade in sand or in a sand-peat mix.

To propagate by division, divide plants carefully in the spring every four or five years, ensuring each divided section contains three or more shoots, and replant immediately.

TROUBLESHOOTING There’s a forbidding list of pests and diseases that target delphinium, from slugs and snails to tiny cyclamen mites, and fungal outbreaks such as powdery mildew, leaf spot, and crown rot, some of which are brought on by summer temperatures and humidity. Fight them with organic fungicide and neem oil. Keep your eye on the plant’s crown, which is susceptible to problems. If the plant becomes heavily diseased, remove it completely, before it can infect surrounding plants. A word of caution: Delphinium seeds and plants (especially when young) are toxic if eaten; keep them away from children, pets, and grazing animals.

This towering bouquet of delphiniums is built around the same color palette. Its flowers are in all stages of bloom along each stem, which are held together in a sizeable flip glass. The “flip” was used back in the eighteenth and early nineteenth centuries to drink heated spiced liquor mixed with beaten eggs. Today its flared rim is ideal for flowers.

HOW TO ARRANGE

CUTTING Wait until many flowers are open before cutting delphinium spires. That said, you can include buds in arrangements; several stems can add variety. Cut the stems at a 45-degree angle so as much water can be absorbed as possible, and then place them in a bucket of lukewarm or cold water. Delphinium foliage isn’t attractive—it’s dense and breaks easily—so it’s best to remove it, especially any that will be underwater in the vase. Prepping these flowers is important, as the stems tend to deteriorate. Clean them well before putting them in the vase.

MAINTAINING Hollow stems need to stay full of water. Recondition delphiniums every two to three days by recutting the stems and changing the water. Keep flowers in a cool area out of direct sunlight.

ARRANGING Delphiniums are very beautiful arranged alone or en masse—they don’t necessarily need other flowers to join in. So let the dramatic flowers stand strong as a single stem in a narrow cylinder. Or mass them in a wide-mouthed vase, using the same color palette; crisscross their stems for balance. They are surprisingly light, so although you may worry that a delphinium arrangement will be top-heavy, simply use a vase with a solid base and let the flowers soar.