A new use for abelias

New abelia cultivars show profuse flowering and stunning panicles of dusty pink sepals.Long valued for its many good qualities, Abelia × grandiflora has been a staple plant for many landscapers. It is a tough plant, very tolerant of drought and highly pest resistantperforms we. It performs well under a variety of conditions. It keeps blooming all summer, when few other shrubs are in flower. Some cultivars boast highly fragrant flowers.

University of Georgia breeder Carol Robacker has been developing improved abelia cultivars, with more stunning floral displays, fragrance, compact growth, reduced size and novel foliage and flowering traits. Many of these new interspecific hybrids have the potential to be grown in a greenhouse as flowering potted plants for spring sales.

Downsizing abelias
To produce a marketable, well-filled container, plants needs to exhibit balanced growth with multiple branches and symmetry and early flowering. Despite their inherent potential, most abelias benefit from pruning to develop a compact, well-branched form. Manual labor for pruning increases production costs. Plant growth regulators are an effective way to achieve growth control, reduce production costs and produce a marketable plant.

Research trials at the University of Georgia sought to evaluate the efficacy of growth regulators to control new abelia cultivars. The long-term goal is to develop a pragmatic production schedule for abelias grown as potted flowering plants that will enable growers to diversify their product mix and increase sales.

Cultivar descriptions
All abelia selections originated from UGA’s breeding program. Some are commercially available under a trade name, while others are in the process of being released or are under evaluation.

‘Plum Surprise’ is relatively dwarf with an unusual weeping form. In March and April, its fine-textured foliage is yellow-green with a few scattered red/purple leaves. In late spring, foliage becomes an emerald green and remains green throughout summer. New stem growth is red, turning to red-brown when older. The most striking features of ‘Plum Surprise’ are fall and winter foliage color and its evergreen habit.

Flowering is sparse and scattered as single blossoms over the foliage. Individual flowers appear white, but on close examination have a purple blush with a pale-yellow throat.

Selection A (tentatively named ‘Sublime’) has stunning chartreuse foliage. It has a compact, upright form that remains tight in pots. In fall, leaves become coppery orange and burgundy. Flowering occurs in August and September, producing large panicles of white flowers and pink sepals.

Selection B has foliage that continually changes color from early spring to late fall and is a heavy bloomer. Winter foliage is burgundy or red. In spring, the foliage is yellow-green with orange shoot tips and dark-purple leaves are sprinkled throughout. Summer foliage is green, though new growth remains orange. Fall foliage is bronze, orange and green. Flowering is heavy, beginning in June and continuing throughout summer. Flowers are white with dark-pink sepals. Panicles are large. This selection has an upright form.

Selection C has bright yellow-green foliage throughout the growing season. New growth is orange. It’s an early-flowering selection, with the first flowers appearing in May. Flowers are purple; sepals are dark pink. Flowers are borne in elongated panicles that hang down over the foliage. This plant is a heavy bloomer, with new flowers opening throughout summer, and the pink sepals make an attractive display until late summer. Plant form is upright and tall.

Selection D has colorful foliage that changes with the seasons. In winter, it is a mix of green, gold, orange, red and burgundy. In spring, the foliage is mostly yellow-green, but with a sprinkling of burgundy and red leaves throughout the canopy. Late spring through summer the foliage becomes light green with orange shoot tips. In fall, foliage becomes golden with orange shoot tips. Flowering occurs in midsummer, with white flowers and pale-pink sepals scattered throughout the canopy. While individual flower panicles are fairly small, they are numerous. The plant is of medium size and grows upright.

Selection E also has colorful foliage. It has yellow-green foliage in spring and summer with bright-orange shoot tips. Flowering occurs in midsummer through fall with white flowers and dark-pink sepals in medium-sized panicles. The plant grows upright and is tall.

Growth regulator treatments
Rooted liners of six abelia cultivars were planted in 1-gallon containers filled with a soilless bark-based mix amended with a slow-release fertilizer. Plants were grown in a greenhouse under natural lighting and photoperiod in spring.

A branching agent (dikegulac-sodium) and a gibberelin inhibitor (paclobutrazol) were evaluated in the trials. Chemicals were applied eight weeks after plant establishment (when roots reached the bottom of the pot). Three of the cultivars received foliar sprays of paclobutrazol (Bonzi, 0.4 percent) at the rate of 30, 40 or 50 parts per million. The other three cultivars received foliar sprays of dikegulac-sodium (Atrimmec, 18.4 percent) at the rate 2, 3, or 4 milliliters per liter. Control plants received sprays of distilled water.

Data were collected three weeks after growth regulator treatment, at which time a second application of Bonzi was made. The plants that received 30, 40 or 50 ppm paclobutrazol sprays were again treated with a 30, 40 or 50 ppm paclobutrazol drench (6 ounces per pot), respectively. The plants that received 2, 3 or 4 milliliters per liter of dikegulac-sodium, were treated with a 30, 40 or 50 ppm paclobutrazol drench (6 ounces per pot), respectively. Control plants received 6 ounces per pot of distilled water.

Final data were collected three weeks after the second growth regulator treatment. Measurements included plant height, width, internode length, shoot number, number of flowering shoots (at bud stage) and phytotoxicity.

Response to treatments
Results indicated that abelia cultivars can be readily controlled by label-recommended rates of paclobutrazol and dikegulac-sodium. In general, the evaluated cultivars showed increased branching, more compact growth and earlier and heavier flowering.

Three weeks after the initial growth regulator treatments, measurements indicated that growth control had not been sufficient with the single spray. Growth control was more evident after the second treatment. Multiple applications at low dose may provide fine-tuned growth control, especially for the more compact abelia cultivars.

Bodie Pennisi is an associate professor and extension floriculture specialist, Carol Robacker is an associate professor and woody plant breeder at the University of Georgia, CAES Griffin Campus; (770) 228-7244; bpennisi@uga.edu; croback@uga.edu.