This study examined the effects of nursery rearing in an array of 51 individual fabricated frames that supported a range of six growing cell sizes at 11 plant spacings in all possible combinations. A continuum of seedling crowding was achieved by placing the same sized cells closer together or by increasing cell size at the same spacing such that soil surface represented 6.2 to 60.4% of horizontal growing space. As seedlings were increasingly crowded during rearing, photosynthate partitioning favored aerial plant parts, shoot:root ratios increased, and soil plugs were less firmly held together by the roots. Decreased crowding produced lower shoot:root ratios and very firm, “root-bound” plugs with high root densities. Soft, undergrown plugs grew roots more actively in field outplantings than did hard, overgrown plugs. These results are discussed in the context of production practices that extend nursery growing to produce large seedlings with high root plug integrity.