Gibberellic acid is one of many plant hormones grouped and labeled as gibberellins. These hormones play a significant role in seed germination, shoot growth, initiation of flowering, and even the timing of leaf drop in fall. Orchard growers choose to apply gibberellic acid to fruit trees to increase twig growth, coax an earlier or more prolific flowering and subsequent production of fruits for harvest, or limit of production to decrease weight stress on branches and increase fruit quality.
Gibberellic acid is sold by chemical manufacturers much like a fertilizer or herbicide product. It may be listed as gibberellin-A3, GA3 to differentiate it from any of the over 130 types of gibberellins known to exist in plants. It may also be ambiguously labelled as "gibberellin." It is synthetically made, according to Great Vista Chemicals Company.
Application of gibberellic acid to fruit trees produces results specific to the plant species, as well as the concentration of the hormone, plant age and timing during the growth season. Too great of a dosage can have negative effects on plants, while an under-application warrants repeated treatments to get the desired increase in growth, according to the California Rare Fruit Growers Association. Therefore, consult your local Cooperative Extension Service or professional agronomist to learn of specific guidelines on the use of plant hormones on fruit trees in your area.
Spraying a fruit tree with gibberellic acid potentially provides many beneficial effects, based on the overall needs of the orchard manager and the time of year. This plant hormone can cause growth and opening of flower buds in early spring, or kill buds if the dosage is a high concentration. Michigan State University notes that gibberellic acid is often applied to young cherry trees to decrease spread of flower-borne diseases and improve fruit quality. In summer, applications act to increase the growth of new twigs and their overall length/size in the growing season. Fall applications can prevent leaf drop on deciduous trees, as well as evergreen trees that shed oldest leaves before the cooler winter months. The University of California comments that tardy leaf drop or delayed fruit maturity is desirable in some citrus or fig trees, for example. If spring frost kills open flowers, sometimes a gibberellic acid spray can coax reset of buds and another flowering.
Various concentrations of soluble molecules of gibberellic acid in water causes species-specific responses. The California Rare Fruit Growers Association lists a generalized comparison of formulation to desired plant reaction. For example, a solution of hormone of 50 to 200 parts per million (p.p.m.) is used to cause early flowering on fruit trees. A solution of 800 p.p.m. coaxes creation of flower buds and over 2,000 p.p.m. is used to cause seeds to rapidly germinate and grow or dormant tissues to sprout. Pastes are also available with a low hormone concentration to smear on plant buds and tissues to increase growth and stem elongation. Interestingly, low concentrations of this hormone cause production of male organ blossoms, while slightly higher levels promote more female flowers.
Gibberellic acid is not a poison, pesticide or herbicide, but should be handled carefully. Avoid getting hormone powder and solution in eyes. No residue should be consumed.