Growth responses from crowding and interspecific competition were examined in 5-year-old plantations of Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco var. menziesii) spaced 17 to 123 cm apart, alone or with either grass or red alder (Alnusrubra Bong.) on three site types in the Oregon Coast Range. Grass and red alder competition and crowding adversely affected growth and standing biomass on a per tree basis. Basal area per hectare and volume per hectare were higher at high densities but these relations are expected to change with time as the larger trees at low densities form fully stocked stands. Grass competition showed greatest effects on growth at the driest site. Although the presence of red alder decreased growth on all sites, the effect was most significant at the coastal site where light is most limiting and moisture is least limiting. If the production of maximum tree size is the primary objective, then low stocking with control of competing vegetation will produce larger trees faster than will other management alternatives.