Plant growth compositions include a mixture of inert compounds and an active component combination of auxin, gibberellin and cytokinin. The plant growth compositions are auxin-dominant, and the ratio of cytokinin to auxin in the active component combination ranges from about 1:10.5 to about 1:4.5. The amount of cytokinin ranges from about 0.1 to 10 wt % by weight of the active component combination in plant growth compositions formulated for in-furrow application to corn plants. Methods of improving plant growth involve in-furrow, seed and/or foliar application of one or more plant types with a plant growth composition. Improvements in plant growth include increases in the average number of bushels produced per acre.