Two multi-year experiments were conducted to determine the influence of planting density and rootstocks on the performance of Montmorency tart cherries (Prunus cerasus L.). Using a constant between-row spacing of 4.5 m, three in-row tree spacings of 4, 3 and 1.5 m were tested with five rootstocks: Weiroot 13, Gisela 6, Krymsk 6, Krymsk 7, and a Prunus mahaleb control. In a second experiment, the comparative effects of five rootstocks spaced 4.5 m × 1.35 m were evaluated: (i) P. mahaleb, (ii) Weiroot 10, (iii) Weiroot 13, (iv) Weiroot 72, and (v) Weiroot 158. With higher tree density, yields increased and tree vigour declined. At higher densities, Weiroot 13 was up to 43% and Gisela 6 16% smaller than Mahaleb, whereas Krymsk 6 and 7 were similar in size to Mahaleb. At the highest density, Mahaleb reduced tree size by 20%. After 7 yr, tree mortality on Krymsk 6 and 7 was greater than the other rootstocks, as was the number of root suckers on Krymsk 7. Cumulative yields, yield efficiency, fruit quality characteristic, and light interception were also markedly influenced by planting density and rootstocks. Overall, evaluated rootstocks ranged in size control from slight to semi-dwarfing, and several showed promise in terms of their induction of high-yield precocity and yield efficiency of the scion. Weiroot selections and Gisela 6 had the greatest beneficial effects on productivity and yield efficiencies. Under experimental conditions, Krymsk 6 and 7 were unsuitable because of their lower cumulative yields and high rate of mortality, respectively.