The growth of plants is repressed by DELLA proteins, nuclear regulators whose activities are opposed by the growth-promoting phytohormone gibberellin (GA). Mutations affecting DELLA protein function were previously used by plant breeders to create the high-yielding semidwarf wheat varieties of the green revolution. gai is an Arabidopsis mutant DELLA protein-encoding orthologue of the wheat semidwarfing genes. Here we describe the development of a transgene that confers ethanol-inducible gai expression. Transient induction of gai causes transient growth repression: growth prior to and after treatment is unaffected. Appropriate ethanol treatments result in dwarf plants that produce the same numbers of seeds as untreated controls. This new technology represents a substantial advance in the applicability of genes encoding mutant DELLA proteins to agricultural and horticultural improvement, enhancing the flexibity with which these genes can be used for the sustainable achievement of increased crop plant yields.