The variability within rows of cultivation may reduce the accuracy of vegetables trails; however, little is known about this variability in protected environments. This study aimed at to assess the variability in greenhouses cultivated with Cucurbita pepo and Capsicum annuum and to verify the effect of borders use and plot size in minimizing this variability. Data from two uniformity trials each crop were used. For statistical analysis, the total of productivity by plant was used, considering the plants arranged in parallel crop rows the lateral openings of the greenhouse and the same plants arranged in columns perpendicular to these openings. Different scenarios were designed by excluding rows and columns to generate the borders in different plot sizes. For each scenario, a variance homogeneity test was performed among the remaining rows and columns and the variance and coefficient of variation were calculated. There is variability among rows and columns in trials with C. pepo and C. annuum in greenhouses and the use of borders does not bring benefits in terms of reduction of the coefficient of variation or reduction of cases of variances heterogeneity among rows or columns. The use of a plot size greater than or equal to or two plants for trials with C. pepo and ten plants for trials with C. annuum provides homogeneity of variances among rows and columns enabling the use of the completely randomized design.