The invention provides methods that enhance the production of biomass from algae that grow autotrophically, heterotrophically, or photoheterotrophically, through the use of plant growth regulators (such as growth hormones, indole acidic acid, etc.) and hormone mimics (phenoxyacetic compounds, etc.). The plant growth regulators or mimics thereof may further increase the proportion of the desired value-added products, such as biodiesel or starch, in the algae culture or the harvested biomass.