December 2014 Culture

Perennial Solutions: Digiplexis ‘Illumination Flame’ By Paul Pilon

As growers, retailers, landscapers and gardeners, we are always looking for a new perennial with the ‘It’ factor or one which illicits ‘OMG’ (as my daughter would say) as the initial reaction when you first see it. Digiplexis ‘Illumination Flame’ is one of those select few plants, which fits this criteria and has certainly garnered much attention and accolades since its introduction.

‘Illumination Flame’ was bred by Charles Valin at Thompson & Morgan in the United Kingdom and is a cross between digitalis and the Mediterranean shrub isoplexis. The ground-breaking new hybrid resulted in a well basal branched, vigorous, beautifully colored and long blooming foxglove.

The real breeding breakthrough is unlike digitalis, which bloom for a few weeks, digiplexis flowers for several months. Flowering begins in the mid spring and continues throughout the summer and until the first hard frost. Digiplexis grows numerous spikes with, as its name implies, flame colored sterile blossoms. The 2-inch tubular, hooded flowers have rich fuchsia-pink tones on the outside, while the inside of the blooms transition from fuchsia pink to golden apricot throats streaked with lavender spots.

Digiplexis can be grown as a perennial throughout USDA Hardiness Zones 8 to 11. However, with its long bloom time, don’t underestimate its value as an annual, tender perennial or a spectacular container plant in colder parts of the country. It prefers locations with partial to full sun and grows to 18 inches wide and 36 inches tall when in full bloom.

With its attention getting spikes of big multicolored blooms and long flower time, digiplexis ‘Illumination Flame’ has earned several awards including the Best New Plant Award at the Royal Horticulture Chelsea Flower Show in 2012, the Greenhouse Grower’s 2013 Award of Excellence, the People’s Choice Award at the New Varieties Showcase at the 2013 Farwest Trade Show and the Grand Prize Winner of the 2014 American Garden Award. ‘Illumination Flame’ makes a great addition to the landscape as a bed or border plant, an outstanding container planting and an excellent cut flower. This new plant is worth trying; seeing is believing.

Propagation

Digiplexis ‘Illumination Flame’ is vegetatively cultivated by means of tissue culture. Propagation is done by a limited number of licensed propagators and self-propagation is strictly prohibited. Vernalized or non-vernalized liners are available; see the availability section below for a current listing of licensed propagators.

Production

Due to its plant size and vigor, it is recommended to plant digiplexis in large container sizes (1-gallon or larger). For the best quality, it is best to plant them in the late summer or early fall, bulk them up and overwinter them in the final containers. However, spring planting vernalized liners will also result in high quality plants. Hybrid foxglove performs well in a growing mix that has both good water holding characteristics and adequate drainage. It is best to plant evenly with the soil line of the liner they were previously produced in.

‘Illumination Flame’ has an average moisture requirement; they prefer to be kept moist, but not consistently wet, during production. Digiplexis will require more frequent irrigation late in the production cycle or during hot and sunny conditions. Do not allow the plants to become overly dry. When irrigation is necessary, water them thoroughly then allow the soil to dry slightly between irrigations.

Hybrid foxglove require moderate amounts of nutrients. Growers using water soluble fertilizers either feed with a constant liquid fertilization using rates of 100- to 125-ppm nitrogen with every irrigation or apply 250 ppm of nitrogen as needed. Controlled release fertilizers can also be incorporated into the growing mix prior to planting using the medium recommended rate, or the equivalent of providing approximately 1.0 to 1.2 pounds of elemental nitrogen per yard of growing mix. Maintain the pH between 5.5 and 6.0 throughout the production cycle.

Unlike standard foxgloves, which produce a single terminal spike, ‘Illumination Flame’ will develop several flower spikes simultaneously. To increase the number of flower spikes and promote the most fullness, it is beneficial to pinch them. Unless the liners have been pinched prior to planting, pinch the plants by removing the growing tips two weeks after planting. Following the pinch, it is recommended to keep the day and night temperatures between 65 and 75° F for three to four weeks to promote healthy lateral shoot development. Lower temperatures (below 60° F) during the bulking phase may result in premature budding. The flower spikes that are done blooming can be removed to promote the growth of additional flower spires.

Plant size can often be maintained by providing adequate space between the plants and growing them on the cool side. Plants that have been pinched by removing the center terminal shoot will be shorter and produce numerous smaller flower spikes. Growing them under high humidity levels and/or photoperiodic lighting will lead to stem elongation. Spray applications of 10-ppm uniconazole (Concise or Sumagic) just as the flower spikes are beginning to elongate can be applied to effectively control plant height.

Insects and Diseases

There are only a few problems associated with insect feeding or plant pathogens growers may observe while growing digiplexis. The primary insect pests of hardy foxglove are aphids, spider mites and Western flower thrips. Growers may also observe Botrytis and crown/root rots on occasion. These pests and diseases can be detected with routine crop monitoring and do not normally require preventative management strategies.

Temperature and Scheduling

There are a couple of strategies to growing digiplexis ‘Illumination Flame’. One strategy, as mentioned above, is to plant them in the fall, bulking them until the lateral shoots are two to three inches long and providing at least four to six weeks of cool temperatures (38 to 45° F) to promote flower initiation. Digiplexis can also be grown in the spring using vernalized liners. After vernalization, grow them with cool temperatures (50 to 60° F) and high light intensities.

The time to bloom after vernalization varies with the production temperatures, time of the year and day length. Planting vernalized liners in the winter (January to February) will take approximately 12 to 14 weeks to produce flowering plants when they are grown under natural light intensities. The number of weeks to finish a winter planting can be reduced to 10 to 12 weeks by providing photoperiodic lighting (creating long days) Digiplexis planted in the early spring (March to April) will flower in as little as six to eight weeks. Growing them cool (<60° F) is the key to producing compact, high quality floriferous plants.

Availability

Digiplexis ‘Illumination Flame’ is brought to the industry by Cultivaris (www.cultivaris.com). Currently rooted liners are available from licensed propagators including James Greenhouses (www.jamesgreenhouses.com), Pacific Plug & Liner (www.ppandl.com), Peace Tree Farm (www.peacetreefarm.com), Plug Connection (www.plugconnection.com) and Skagit Gardens, Inc. (www.skagitgardens.com).