Perennial Solutions: Erysimum 'Fragrant Star'

December 6, 2012 - 15:54

This variegated wallflower performs well in perennial beds as well as containers, and can even be used as a cut flower.

Many growers seek spring flowering perennials with attractive foliage characteristics. Erysimum ‘Fragrant Star’ is an exciting stable variegated spring blooming wallflower, destined to earn a place in many perennial programs. ‘Fragrant Star’ is easy to grow and has great potential for use in spring programs as well as in the landscape.  

Erysimum ‘Fragrant Star’ is a compact selection forming 15- to 18-inch high by 18- to 24-inch wide dense, evergreen mounds of striking creamy yellow and green variegated foliage. In mid spring, it develops chocolate-purple flower buds that contrast well with the variegated foliage and golden flower clusters. The bright yellow scented blooms last several weeks; the extended bloom time is attributed its sterile nature.

‘Fragrant Star’ is a stable sport of erysimum ‘Fragrant Sunshine’ which was discovered in the United Kingdom by David Tristram. It thrives in locations with full sun throughout USDA Hardiness Zones 6 to 9. This variegated wallflower is versatile and performs well in perennial beds, borders, rock gardens and containers. Additionally, ‘Fragrant Star’ attracts butterflies into the landscape, is deer resistant and drought tolerant once established, and can be used as a cut flower.  

With its variegated evergreen foliage and cheerful blooms, ‘Fragrant Star’ nicely compliments most containerized perennial programs and is a particularly nice choice for landscape uses.

Propagation

Erysimum ‘Fragrant Star’ is vegetatively propagated by tip cuttings. It is a patented cultivar; asexual propagation without a license is prohibited.  

Before sticking the unrooted cuttings (URCs), moisten the rooting medium in the liner trays. After the cuttings are stuck, place them under a moderate misting regime. To accelerate rooting and improve uniformity, spray the cuttings with 1,000-ppm IBA soluble salts within 24 hours of sticking. Fungus gnat larvae can often become problematic; a preventative program to control them is recommended after the cuttings are stuck.

Maintain moderate to high mist frequencies for the first few days of propagation, then slightly reduce the amount of misting until rooting begins. Once roots are present, further reduce the misting frequency and apply 75- to 100-ppm nitrogen at least once per week. Remove the cuttings from the mist once they are rooted.  

The cuttings usually take approximately three weeks to root with soil temperatures ranging from 68 to 72° F. It is beneficial to pinch the terminal shoots when the plants reach three inches tall to promote branching. Liners take approximately five to seven weeks from sticking to become fully rooted and ready for transplanting.  

Production

Growers commonly produce erysimum in 1-quart to 1-gallon sized containers. ‘Fragrant Star’ performs best in well drained growing mixes. When planting, the liners should be planted so the original soil line of the plug is even with the surface of the growing medium of the new container. If the liners were not pinched prior to transplanting, it is beneficial to soft pinch the plants when they have approximately 2 inches of new growth to promote lateral branching and improve fullness. Avoid pinching or cutting them too low or they will not develop branches very well.

During production, wallflowers require light to moderate fertility levels. Nutrients can be delivered using water soluble or controlled-release fertilizers. Growers using water-soluble fertilizers apply 100- to 150-ppm nitrogen with every irrigation or use 250 ppm as needed. Controlled-release fertilizers are commonly applied as a top-dress onto the media surface using the medium recommended rate on the fertilizer label or incorporated into the growing medium prior to planting at a rate equivalent to 1.0 to 1.25 pounds of elemental nitrogen per yard of growing medium. The pH of the media should be maintained between 5.8 and 6.4.  

‘Fragrant Star’ should be kept moist, but not saturated, during production. In general, they require average amounts of irrigation; however, as crops matures they will require slightly more irrigation than they used early in the production cycle. When irrigation is required, water them thoroughly and allow the substrate to dry slightly between waterings.  

With its naturally compact growing habit, controlling plant height should not be necessary.  Under certain circumstances, it may be necessary to use chemical plant growth regulators to control the growth of Erysimum. When the crop needs to be toned, spray applications of 5-ppm uniconazole (Concise or Sumagic) are effective. Otherwise, growing them with adequate spacing between the plants is usually sufficient.

Insects and Diseases

Wallflowers are susceptible to several insect pests and diseases during production and in the landscape. Aphids, spider mites and thrips are the most prevalent pests growers observe. The primary pathogens which infect erysimum are Botrytis, downy mildew, powdery mildew, Rhizoctonia, and rust diseases. None of these insect pests or diseases requires preventative control strategies.  Insects and diseases can be detected with routine crop monitoring; control strategies may not be necessary unless the scouting activities indicate actions should be taken.

Scheduling

With its attractive foliage, erysimum ‘Fragrant Star’ can be marketed as a foliage perennial or in full flower. Typically, growers market flowering plants in the mid spring. To produce the fullest containers with the most bloom, it is best to bulk ‘Fragrant Star’ in the final container prior to overwintering. Allow a minimum of six weeks for quart-sized containers and up to 10 weeks for bulking 1-gallon sized containers.

Erysimum has an obligate cold requirement for flowering. They can be vernalized in the final container or as large plugs (72-cell or larger) for a minimum of six weeks at 35 to 44° F. It is best to bulk up large container sizes prior to overwintering. Planting vernalized liners into large containers in the late winter or early spring usually results in plants with few flowers. However, small container sizes can be planted in the spring using vernalized liners and will generally have enough flowers for this sized plant.  

After vernalization, growers most commonly grow them under natural lengths and cool temperatures.  When they are grown at 60 to 65° F, ‘Fragrant Star’ takes about six to seven weeks to flower.  Non-flowering plants can be produced throughout the growing season from spring to fall by planting unvernalized liners and allowing approximately 10 to 12 weeks to fill out the container.  

Availability

Erysimum ‘Fragrant Star’ was brought to the market by Plant Haven Inc. (www.planthaven.com). Rooted liners are available from several licensed propagators including Green Leaf Plants (www.glplants.com), Pacific Plug & Liner (www.ppandl.com) and Skagit Gardens Inc.
(www.skagitgardens.com).

About The Author

Paul Pilon is a horticultural consultant, owner of Perennial Solutions Consulting (www.perennialsolutions.com), and author of Perennial Solutions: A Grower’s Guide to Perennial Production. He can be reached at 616.366.8588 or paul@perennialsolutions.com.

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