Gibberellic Acid for Shrubs

Natural Function

• You don't have to purchase a product containing gibberellic acid to have it play a role in the shrubs in your landscape. Gibberellic acid is a growth hormone present in plants, including woody ornamentals. In shrubs, temperature changes apparently cause shifts in hormonal barriers, advises Claude W. Blakely, Laurens County, South Carolina Master Gardener. Chilling temperatures in fall allow an increase in gibberellic acid hormone concentration, and warming temperatures in spring allow these concentrated hormones to produce new growth.

Propagation

• Gibberellic acid can facilitate shrub propagation by helping with seed germination. Not all shrubs respond to this treatment, however. Examples of shrub seeds that do benefit from gibberellic acid treatment include junipers (Juniperus spp.), mountain laurels (Kalmia spp.) and bayberry (Myrica spp.), according to Texas A&M University horticultural professor, Fred T. Davies. Commercial nurseries may use gibberellic acid treatments to get better seed-germination rates, but other techniques may be more efficient shrub-propagation methods. Techniques such as micropropagation are other important commercial shrub-production processes, notes Davies.

Stems and Flowers

• Not surprisingly, as a growth hormone, gibberellic acid affects shrub size. One effect of treating Jasminum spp. with the acid, for example, is increased shoot growth, notes P. Sridhar in a review of research on the topic. Sridhar found that gibberellic acid increased the leaf area, as well as the length of jasmine shrubs' shoots. It also delayed flowering. This is a technique commercial growers can use in conjunction with other treatments to influence the timing of flower production. Gibberellic acid treatment lowered the quantity of flowers produced on jasmine shrubs, however.

Fruit

• Gibberellic acid can also help shrubs set fruit. Blueberries (Vaccineum spp.) benefit from this treatment. Spraying with commercial products containing gibberellic acid late in the bloom period may aid pollination, when bees don't do this work because conditions are cool, rainy or windy, according to Michigan State University horticulturalists. Georgia blueberry growers report success using gibberellic acid to help boost fruit set from frost-damaged blooms.