Banana (Musa spp.) is an important perennial crop in tropical countries. Testing improved germplasm and/or agronomic practices to increase productivity requires accuracy and precision. The objectives of this study were to determine the optimum plot size (i.e., number of plants per experimental plot) and the number of replications to detect significant true mean differences in bunch weight (i.e., commercial yield) between treatments. Three uniformity trials of the cultivar Valery grown in Ultisols under two different management practices (alley cropping of banana with multispecies hedgerows and monocropping of banana in cleared land) and at two locations in the humid forest zone of sub-Saharan Africa were used. The methods of maximum curvature and comparison of variances were used to determine optimum plot size, while the number of replications was estimated by Hatheway's method. This statistical procedure considered an expected relative magnitude of differences between treatment means at a specific probability level and the relationship between the coefficient of variation and soil heterogeneity. The experimental plot should have a single row of 5 plants for banana in an alley cropping system, whereas single rows of 20 plants plot−1 are required in a monocropping system. This finding indicates that alley cropping of banana with multispecies hedgerows may be an adequate system not only to maintain diversity but also for greater efficiency in testing improved germplasm. A table was developed, indicating the expected detectable true mean differences for bunch weight per plant for different number of treatments tested (5–30), plants per plot (5–40), replications (2–6), and management practices. This table allows musa researchers to select minimum trial sizes, according to their objectives and available resources. For example, when 30 treatments are tested in alley cropping fields, using randomized complete block designs with two replications of 10 plants plot−1, a true bunch weight mean difference of 15% may be found to be significant.