Delphiniums are one of the hardiest perennials found in Northern Utah gardens. However, they are as beautiful as they are tough. Delphiniums are normally associated with large, English-style gardens, where they are nestled amongst old-fashioned roses, lavender, blue salvia and other colorful flowers. Delphiniums have been the subject of many paintings and poems.
Tall and stately, delphinium flowers come in purple, white, pink and even yellow blossoms, says Jerry Goodspeed, Utah State University Extension horticulturist. Recent breeding has even developed hardy delphiniums in red and orange hues. However, the most popular are still the purple, lavender, white and bi-colored varieties.
“Larkspur are often confused with delphiniums. Larkspurs are actually annuals that are closely related to delphiniums,” he says. “They reseed themselves most years, so they are often confused with perenials.
“Larkspur flowers are a bit smaller, but come in the same wonderful colors as delphiniums. They are normally sold as mixes, which means you get a large splattering of many colors. They are very showy and bloom throughout most of the summer.”
Delphiniums bloom on tall spikes, so they are commonly used in borders or as background plants in the landscape, Goodspeed explains. They bloom in early summer and often again in late summer or early fall. The tall spikes of these flowers need some type of support while blooming so they don't fall. A thin bamboo stake, or other non-intrusive support works best. Tie the flowers up just before they start to bloom.
“Delphiniums prefer a deep, organic-rich soil but, with some care, can be grown in about any type,” he says. “By planting them in the early spring, they usually bloom the first year. Because they are so quick to bloom, many people treat them as annuals, buying new plants every year. They are actually a short-lived perennial and prefer short, cool summers to long, hot periods.
“After planting, fertilize delphiniums with an all-purpose fertilizer,” he adds. “They are somewhat heavy feeders, so they may need to be fertilized every month while they are growing. Water them deeply and infrequently, as with most perennials.”
Once the first tall flower spike is through blooming, remove it right below the lowest flower, Goodspeed says. Leave the foliage to give the plant area to produce more sugar (energy) for future blooms. New small shoots should begin to grow near the base of the plant soon after the blossom has been trimmed. These form smaller flower spikes later in the summer or early fall.
There are a number of different hybrids worth mentioning and to consider for a perennial border, he says. Can Can, Guy Langdon and Purple Triumph are dark purple varieties. Leonora, Summer Skies, Fanfare and Crown Jewel have light blue to lavender-colored blossoms. Some popular white varieties include Lilian Bassett, Sandpiper and Shasta. There are many other great varieties and colors available. Ask your local nursery or garden center for the ones they carry.
For more information, contact your local USU County Extension office.
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