Growth regulators are any organic or synthetic compounds that influence growth and multiplication. They are produced in plants (e.g. in growing buds) to control the growth.

Auxins influence cell enlargement, root initiation and adventitious bud formation. They suppress the initiation of lateral buds (which is the bud of choice for ensuring genetic stability). Auxins are commonly used in tissue culture media, either combined with cytokinins during the multiplication stage or without cytokinins for the rooting stage.

Cytokinins, formerly called kinins, are required in tissue culture media for cell division, shoot multiplication and axillary bud proliferation. They help delay senescence (aging), and they influence auxin transport. If cultures are too spindly, increased cytokinin will help foster shorter, stouter stems.

Gibberellins are a group of naturally occuring substances that influence cell enlargement and stem elongation. Kurasawa noted in 1926 that secretions from a fungus (Gibberella fujikuroi) resulted in abnormally rapid growth in rice seedlings. The substance was gibberellic acid, which was later isolated in crystalline state from both fungi and higher plants.