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. With their showy foliage in a number of colors, Japanese barberry (Berberis thunbergii) cultivars are among the most attractive ornamental plants in summer landscapes. 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 Japanese barberry selections are adorned with small colorful leaves that often turn a brilliant red in the fall. Red berries on red-foliaged cultivars and lime-green berries on green- and golden-leaved cultivars 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, Japanese barberry selections are generally rust-resistant and practically pest- and disease-free.

Several nurseries, which may be attempting to minimize heat stress by overcompensating with irrigation, have expressed difficulties in producing high-quality container-grown golden barberries. Many growers have even shifted production capacity to less troublesome crops.

In terms of research in barberry species, most to date has focused on medicinal uses or pathogenicity of barberry, with little research being done to evaluate ornamental production or propagation of barberry. Perhaps the prickly thorns of barberry species serve as a deterrent to research projects with this crop.

In particular, no propagation or production research has been reported for golden barberry cultivars. Therefore, AAES researchers decided to take on that task in two studies: one, to evaluate the effects of shade in barberry propagation; the other, to look at the impact of light intensity and irrigation regimes on container production of four golden barberry cultivars.

The propagation studies were initiated on April 29, 1998, and Sept. 18, 1998, using three- to four-inch-long softwood medial stem cuttings of Bailsel (Berberis koreana x thunbergii). Bailsel (Golden Carousel^TM ), a relatively new golden selection, 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, Minn. Bailsel has an upright and arching growth habit similar to Rose Glow (Berberis thunbergii var. atropurpurea), but it has golden yellow hues on young foliage throughout the growing season that turn to orange and red in the fall.

Cuttings were taken from three-gallon stock plants growing under a 50% shade in Auburn. Japanese barberry species are generally rooted with indole butyric acid (IBA) solutions of 1,000 to 5,000 parts per million (ppm), so cuttings were treated with 1,250 ppm IBA for three to five seconds, then stuck in open trays lined with 24-cell inserts that were filled with a pinebark/sand 6:1 (by volume) substrate amended with five 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.

Initial signs of root development occurred for all treatments about 20 days after treatment. After 57 days, root ratings, or the number of roots, 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).

Effects of Shade Level on Propagation of Bailsel (Berberis koreana x thunbergii)
Treatment	Root ratinga		Viabilitya		Root dry weighta
	Study 1b	Study2b	Study 1	Study 2	Study 2
60% shade	2.8	2.7	86	100	9.32
70% shade	4.1	3.4	97	97	9.27
80% shade	4.0	4.1	100	96	9.27
a Root ratings on 0-5 scale; viability in percent; root dry weight in grams.
b Study 1 conducted from April 29 to June 25,1998; Study 2 conducted from Sept. 18 to Nov. 14, 1998.

Overall foliar color was improved to a uniform golden hue under 70% and 80% shade levels, compared to cuttings rooted under 60% shade, which developed a red hue or exhibited desiccation (see photo). Root dry weights were greater for cuttings under the 60% shade levels than 70% or 80% shade. That means the plants rooted under 60% shade had fewer roots, but the roots were larger and longer than in the 70% and 80% shade groups.

Golden barberry propagation under 60% shade (left), 70% shade (center), and 80 % shade.

Based on the results of this study, the researchers believe 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 improve as shade levels are increased.

The objective of the second study was to evaluate effects of light intensity and irrigation regime on four container-grown golden barberry cultivars: Monlers (Gold Nugget^TM), Aurea, Bogozam (Bonanza Gold^TM), and Bailsel (Golden Carousel^TM). In April 1998 and April 1999, three-quart stock plants were potted into three-gallon containers in a pinebark/sand 6:1 (by volume) substrate amended with 18 pounds per cubic yard of 15-9-11 Osmocote+, 1.5 pounds per cubic yard Micromax, and 5.0 pounds per cubic yard dolomitic limestone. Multiple replications of plants were grown under 30% shade or in full sun at four different irrigation rates (0.5 inch, 1 inch; 1.7 inches, and 2.7 inches per day).

Irrigation had no effect on the total overall growth for each cultivar in either year. Results of this study indicate that there is no benefit in overall growth when irrigation is increased above 0.5 inch per day. In other words, neither plants grown in full sun nor those grown in shade grew any larger with increased water.

On the other hand, shade did influence plant growth. In 1998, Aurea in 30% shade had greater growth than plants grown in full sun. There were no differences in growth for remaining cultivars grown under 30% shade compared to full sun, other than a slight difference in April 1998 for Bailsel. In 1999, light intensity had no effect on growth of either cultivar initially. However, by June, Bailsel plants grown in 30% shade were larger and remained so for the rest of the growing season, with shade plants 22% larger at the conclusion of 1999 than plants grown in full sun. By August 1999, Aurea plants grown in 30% shade were larger than full-sun plants, with shade plants 26.1% larger than plants grown in full sun at the end of 1999.

This study suggests that golden barberry selections are actually more suitably propagated in part-shade environments. From a container production standpoint, barberry species may actually be better suited for production in modified growing environments where elevated container temperatures are not as extreme. While various selections of barberry are thought of as tough, full-sun plants and typically have been used in landscape combinations with yucca, lantana, crape myrtle, and similar full-sun plants, barberries may actually perform better in landscapes as companion plants where azaleas, hostas, and impatiens are grown.