Brian H. Murphree, Jeff L. Sibley, D. Joseph Eakes, and J. David Williams

The barberries, including both evergreen and deciduous species, are commonplace in landscapes across the United States and throughout the world. The Japanese barberry (Berberis thunbergii), a deciduous species, was introduced to the United States as an ornamental plant in 1864 by a Dutch botanist, Carl Peter Thunberg. Cultivars of Berberis thunbergii are among the most attractive ornamental plants in summer landscapes due to showy foliage in a number of colors. Despite prickly thorns, barberries continue to be a homeowner favorite and collectively, come close to being no-maintenance plants throughout USDA Hardiness Zones 4-8. Many Berberis thunbergii selections are adorned with small colorful leaves often turning a brilliant red in the fall, along with red berries which last through the winter on some selections. Although some species of barberries have been banned where wheat is a major crop because of the role they play in transmitting black stem rust to wheat, Berberis thunbergii selections are generally rust-resistant and practically pest and disease free.

Most research in Berberis species has focused on medicinal uses or pathogenicity of barberry with little research evaluating ornamental production or propagation of Berberis species. Berberis thunbergii species are generally rooted with indole butyric acid (IBA) solutions of 1,000 to 5,000 parts per million (ppm). Studies have shown that cuttings of Berberis thunbergii and B. thunbergii ‘Atropurpurea’ have an increased rooting response when stock plants are grown at less than full sunlight. However, there have been no reports concerning propagation of golden barberry cuttings under different light intensities. This study was conducted to evaluate the influence of shade on propagation of golden barberry.

METHODS
Studies were initiated on April 29, 1998 and September 18, 1998 using 3-4 inch long softwood medial stem cuttings of Berberis koreana x thunbergii ‘Bailsel’ (Golden Carousel^TM). ‘Bailsel’ is an interspecific cross between Berberis koreana and Berberis thunbergii ‘Aurea’ which was discovered as a chance seedling in field plots at Bailey Nurseries, Inc., in St. Paul, Minnesota. ‘Bailsel’ has a growth habit that is upright and arching with golden yellow hues on young foliage throughout the growing season that turn to orange and red in the fall.

Cuttings were taken from 3-gallon stock plants growing under a 50% shade in Auburn, Alabama. Cuttings were treated with 1,250 ppm IBA (Dip ‘N Grow) for 3-5 seconds, and stuck in open trays lined with 24-cell inserts filled with a pinebark/sand 6:1 (by volume) substrate amended with 5.0 pounds per cubic yard of dolomitic limestone. The experiment was conducted in a standard greenhouse under intermittent mist with treatments consisting of three shade levels based on full sun ambient light. Treatments were 60% shade, 70% shade, and 80% shade.

Subjective foliar color ratings were made weekly. Root dry weights were collected only for the study conducted in September. Rooted liners were harvested 57 days after treatments began (DAT). Roots rinsed free of substrate were evaluated using a root rating scale 0 - 5 with 0 = plants having no roots and 5 = plants that were heavily rooted.

RESULTS
Initial signs of root development occurred for all treatments about 20 DAT. After 57 days, root ratings were higher in plants under 70% and 80% shade than 60% shade. Viability was lower and desiccation was greater among plants under the 60% shade level than those occupying either the 70% or 80% shade level (see table). Overall foliar color was improved under 70% and 80% shade levels (a more uniform golden hue) compared to cuttings rooted under 60% shade which developed a red hue or exhibited desiccation. Root dry weights were greater for cuttings under the 60% shade levels (see table) than 70% or 80% shade.

Based on the results of this study, we believe Berberis koreana x thunbergii ‘Bailsel’ can be successfully propagated from softwood cuttings in early summer or fall with solutions containing 1,250 ppm IBA. Furthermore, leaf retention, leaf color, and liner quality are improved as shade levels are increased. While various selections of barberry are thought of as tough, full-sun plants, this study along with other work suggests that golden barberry selections may actually be more suitably propagated in part-shade environments.