Osmo-adjusting solutes, particularly polyols and/or monosaccharides, are used to control the growth of plants. In particular, aqueous solutions of sorbitol or xylitol are used to reduce plant height and increase stem diameter. The solutions preferably include between about 0.05 and about 25 weight percent of the osmo-adjusting solute, and are applied to the root zone by drenching regularly or prior to transplanting. The solutions are also shown to be effective for conditioning plants for hardiness against certain environmental and handling stresses.