Crop Culture Report: Delphinium New Millennium Series
The delphinium New Millennium series was bred by New Zealand’s Terry Dowdeswell and is available from Jelitto Perennial Seeds. It includes a magnificent color range with semi-double to double blossoms.
Pierre Bennerup, founding president of the Perennial Plant Association and CEO of Sunny Border Nurseries in Kensington, Conn., describes the flowers of these hand-pollinated F1 hybrids as “bigger and fatter” than the Pacific Hybrid strain. John Schroeder, founder and CEO of Valleybrook Gardens in Abbotsford, BC, Canada, said the New Millenniums overwinter very well in the ground and “come back stronger every year.” Chad Walters, inventory manager for Walters Gardens in Zeeland, Mich., “made the switch from Pacific types to the New Millennium hybrids a number of years ago because the flowerscapes are sturdier” and full in appearance.
In 2008, the rich-pink flowering ‘Sweethearts’, with a white bee in the flower center, received an Award of Garden Merit from the Royal Horticulture Society. ‘Dusky Maidens’, the pink counterpart with a darker bee, received the Perennial Plant award from the International Hardy Plant Union in Hillegom, Holland. ‘Green Twist’, white with a green tinge and white-green bee; ‘Royal Aspirations’, deep blue with a white bee; ‘Double Innocence’, double pure cream white; and ‘Pagan Purple’, double blossoms in dark blue-purple, are among the 17 different New Millennium offerings, including the New Zealand Hybrid Mix.
In England, where taller border delphiniums with handsome, long, flowering spikes were long ago anointed queen of the garden, the New Millennium series has drawn comments like “quantum jump” and “excellent display.” Although delphiniums are good sellers all over the temperate world, they often are considered a challenge for home gardeners with anything less than an ideal English climate.
The first-year-flowering New Millennium series has the virtues of improved winter hardiness and a sturdy growth habit. There also are promising reports for better suitability in warmer, more humid summer climates, where nights cool down into the 60s and plants are planted in well-drained, organic enriched soils, and provided some shade in the hottest portions of the day.
In addition to bold architectural border appeal, these durable delphiniums have great potential as cut flowers from June to September. Topping out at 60 inches tall, the delphiniums have thick stems that diminish the need for staking, though it would be a good precaution again passing summer thunderstorms. New Millennium varieties prefer full sun and should be spaced 32 inches apart in humus-rich, well-drained soils with a pH of 6.2-7.2. Consider planting with Agastache mexicana ‘Sangria’, Alcea rosea var. nigra and Angelica gigas.
Plants sown in July and August will grow large enough to overwinter outside or in a cold poly tunnel and are perfect for spring sales. But seeds can be sown anytime and may be easiest sown in the winter months. Overwintering fall-sown plugs in a cold house sometimes invites fungal problems.
There are no cold requirements and if sown as early as January, the New Millenniums will flower in June. Two to three seeds can be sown per 72- or 128-plug tray, but are ideally sown — and covered lightly (1⁄8- to 1⁄5-inch) with fine vermiculite — in deep, open flats and pricked out as they germinate. Some growers have experienced improved germination with an initial moist/cold stratification, placing the seeds in media at 35-42° F for three to four weeks prior to introducing warm temperatures. Differential warm day (60-72° F) and cooler nighttime (55-60° F) germination temperatures, and high humidity, are very important. Smaller growers have maintained humidity by covering seed flats with five to 10 sheets of newspaper kept moistened until germination and immediately withdrawn. Temperatures above 80° F and below 50° F should be avoided. Germination commences in two to three weeks, and more than 80 percent germination usually can be expected. Some growers have reported good results with constant 60° F temperatures in germination rooms.
Fertilization and Finishing
A constant feed of 50-ppm nitrogen can begin two weeks following germination and can be increased to 75-100 ppm twice a week with an EC rate of 1.0 in the third week until transplant. Germination to transplant requires four to six weeks. Cut back foliage once when transplanting, and again four weeks later to keep compact. One plant can be potted into a quart, or two plants per gallon size, and can be finished in another six to eight weeks. Fertilize with a balanced constant feed at 100-150 ppm once a week in the greenhouse with an EC rate of 1.5. Higher outdoor fertilization rates may apply. Avoid overwatering at every stage to prevent Pythium and Phytophthora. The introduction of the Trichoderma fungus has helped reduce the incidence of soil-borne fungi. Insect problems are seldom serious but thrips, aphids and whiteflies are seen occasionally.