Abstract The introduction of the fungal pathogen Cryphonectria parasitica (Murr.) Barr. decimated American chestnut ( Castanea dentata (Marsh.) Borkh.) throughout its native range in North America. A blight-resistant backcross hybrid form of American chestnut has been developed, and these backcross trees are likely to be incorporated into restoration programs in the near future. To help guide future afforestation efforts, this study examined juvenile (five growing seasons) morphological and physiological competitive aspects of American chestnut grown in a plantation setting with northern red oak ( Quercus rubra L.) and black cherry ( Prunus serotina Ehrh.) in Indiana, USA. Species were grown in seven possible species combinations including both monospecific and polyspecific combinations at three densities (1 × 1 m, 2 × 2 m, and 3 × 3 m). Despite an initial advantage in height, American chestnut exhibited the lowest relative height growth in the 2 × 2 and 3 × 3 m spacings, resulting in less total height compared to the other two species 5 years after planting. Relative height growth, as well as final absolute heights, were comparable among species in the 1 × 1 m spacing. Black cherry exhibited 2–3 times greater relative ground-line diameter (GLD) growth compared to oak and chestnut at all spacings. Linear regressions showed that growth was generally proportional to net photosynthesis ( A ) for all species. Increases in A likely resulted from increases in leaf nitrogen concentration. Chestnut exhibited lower A than cherry and oak in years 2 and 3, but no differences occurred in year 4. Additionally, chestnut had significantly higher predawn leaf water potential (leaf Ψ pd ) in year 4, reflecting greater drought stress in cherry and oak. While black cherry grew most aggressively, northern red oak and American chestnut performed acceptably, with high survival rates and moderate growth, especially in the 1 × 1 m spacing. American chestnut had the poorest stem form overall, but fared better in the 1 × 1 m spacing where the crown competition factor (CCF) was highest. Hence, an intermediate spacing between 1 × 1 and 2 × 2 m could optimize chestnut’s growth and stem form. Mixture effects may be attributed mainly to individual species growth characteristics rather than inter-specific interactions during this juvenile developmental stage.