Lauterbach: Delphiniums need to be planted in full sun, sheltered from wind

Special to the Idaho StatesmanMay 16, 2013 

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To grow delphiniums the seed must be fresh and collected from first-year crosses to ensure health and vigor.

COURTESY OF TERRY DOWDESWELL AND WWW.DELPHINIUM.CO.NZ/

To a fan of delphiniums, a gap or two in a spike of flowers is as unforgiveable as a missing button on a new shirt. When spikes grow short or frowsy, even a devoted fan may lose interest in that flower.

There are some delphinium breeders who are paying attention to vigorous plants with fully-flowered spikes and true colors. In England, growers may buy crown cuttings and grow from them, but we can't import them, so we must grow them from seeds. Seeds must be collected from first-year crosses to sustain plant vigor, and not all seed sellers are careful about discarding inferior plants.

One of the best seed collectors and vendors is Terry Dowdeswell in New Zealand, and that bodes well for us in the Treasure Valley.

Why?

Because to grow delphiniums from seed, one should use fresh seed. By spring our seed from delphiniums grown in the Treasure Valley is several months old, but New Zealand seed is being harvested at this time as its growing season is over and winter's just beginning.

Edwards Greenhouse has been growing Dowdeswell's "New Millenium" delphiniums for more than ten years now, a variety of English delphiniums bred and cultured by Terry Dowdeswell in Wanganui, NZ. They're very impressive specimens. British garden writer Graham Rice refers to Dowdeswell as "the finest delphinium breeder in the world."

New Millenium delphiniums grow to a height of five to seven feet, and are fairly easy to care for.

They should be planted out in a wind-sheltered location in full sun or with a support inserted into soil when the delphinium is planted. You may feel foolish inserting a six-foot stake next to a three-inch plant, but the seedling will catch up. In our climate, they probably would do best with a bit of afternoon shade on hot days.

Delphiniums grow best in soil enriched with organic matter, and seem to thrive in our alkaline conditions. Some growers use bone meal, others use fertilizer such as Dr. Earth when they plant.

I recommend you use a face mask if you use bone meal, because a gust of wind can blow it into your respiratory system, and I think bone meal could transmit Creutzfeld-Jakob disease. If you have a pet dog, it will be tempted to dig out the plant, lured by the odor of bone. Dogs react similarly to blood meal.

Anju Lucas, head of perennials at Edwards Greenhouse, says delphiniums are short-lived perennials, so you get the most for your money if you buy small plants such as in four-inch pots.

The main challenge is to protect the plant from wind and slugs. Roots should be kept cool and moist, never soggy or dry, and the best way to do that is to use a good mulch. Unfortunately slugs love to hide in mulch during the day, so traps are in order.

Delphinium flowers' centers are usually a different color than the richly vivid, usually colorful, petals. Some cultivars have white petals, contrasting with black "bees." Centers, containing the reproductive parts, are properly known as "bees." Seed descriptions identify the color of the petals and the bees.

In addition to the spectacular Dowdeswell delphiniums, there are dwarf versions, called "New Heights," now on the market. They've been developed in the Netherlands from standard English delphiniums crossed with a natural sport, short and stout for a delphinium. These New Heights delphiniums look just like the English delphiniums, but they grow to only three or four feet tall. I don't know whether they're available here yet.

Once any delphinium has finished blooming, cut the spike just below the last flower, and you'll get a second flowering, a little less spectacular than the first. Some growers such as Stella Schneider cut them back almost to the ground, and put a pebble over the hollow stem to prevent water's entry. The plant will grow a new stalk and bloom a second time. For winter, cut the spike back to the rosette of leaves, but leave the leaves intact.

Some fans of delphiniums feel producers of seed have not been careful about keeping seed true for color or full-blossoming capability. Pacific Giants, once the favored American delphinium in gardens, is one that has been criticized for deterioration of color and fullness of blooming.

Send garden questions to melauter@earthlink.net or Gardening, The Statesman, P.O. Box 40, Boise, ID 83707.

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