Just as there are places I would like to visit, but will never see, and experiences I wonder about, but will never have (I’m looking at you, bungee jumping), there are plants that I admire and desire, but will never grow. These are plants that require specific growing conditions, a ridiculous amount of pampering, and a climate that I don’t live in. At the top of this list are delphiniums.
The darlings of the English cottage garden, delphiniums are spectacular. Their shape, height, and jewel-like colors make them showstoppers and a great counterpoint to roses and other perennials that mound or spread. I’ll never be able to grow them successfully, but that doesn’t mean I don’t yearn to see their impressive spires hovering over the other flowers in my perennial border.
Delphiniums are in the buttercup family and related to the shorter and leggier larkspur. The garden delphiniums available in the U.S. are hybrids of varying heights: The Elatum group is tallest, with the classic dense flower stalk, the Pacific Giants group is a foot or so shorter, and the Belladonna group tops out at 3 to 4 feet, and has branched flower stalks.
Plants bloom in June and July in almost every hue, but the classic colors are blue, purple, pink or white with contrasting white or black “bees” – the flower’s center. Hummingbirds, butterflies and bees love delphiniums. Varieties can be as short as two feet and as much as eight feet tall. Delphiniums are short-lived and individual plants can be expensive, especially since they look best in clusters of five or more. They can be started from seed, but it takes awhile before plants are large enough to flower.
While delphiniums will make any garden the envy of the neighborhood, they are not easy plants to grow. They require prime garden real estate and demand constant attention. Staking, feeding, consistent watering and constant vigilance for pests and diseases are all necessary. But if you’ve got the right climate and are game for a challenge, here’s what you need to know.
How to grow:
Site: Hardy in USDA Plant Hardiness Zones 3 to 7. Not recommended for humid climates. The site should be sheltered from strong winds and rain. Against a fence is ideal. Taller varieties are perfect for the back of the border.
Sun: Delphiniums need full sun, a least six hours a day, but partial shade in hotter areas. They like a cooler climate, the kind found in the Pacific Northwest or coastal Maine.
Soil: Rich, well drained and on the alkaline side. Mix some good quality compost into the soil before planting. Soil should be kept moist. This plant is not drought-tolerant.
Plant: Don’t plant the crown too deep, or it will rot. Space plants one to three feet apart, depending on the variety. They look best planted en masse but air needs to circulate between plants.
Care: Delphiniums have hollow stalks which snap easily and so need to be staked. They also need to be deadheaded, and fed throughout the summer. Mulch after planting and keep weeded. Water regularly, but do not overhead water or get the foliage wet, which can lead to leaf spot.
After bloom, cut the flower stalk right down to the bottom foliage and the plant may send up another flower stalk in late summer. Plants are vigorous growers; divide clumps every two to four years.
Pests: Slugs, snails, aphids, mites, leafhoppers, leaf miners, stem borers. Deer and rabbits, thankfully, leave them alone.
Diseases: Rust, gray mold, powdery mildew, botrytis, leaf spot, crown, stem, and root rots. This is not an exhaustive list.
It’s unlikely that my shady and humid garden will ever host delphiniums, making me a bit envious of the dormouse in the A.A. Milne poem, the Dormouse and the Doctor:
There once was a Dormouse who lived in a bed
Of delphiniums (blue) and geraniums (red)
And all the day long he'd a wonderful view
Of geraniums (red) and delphiniums (blue).
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By Heirloom Roses
Photographs courtesy of Heirloom Roses
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