A previously proposed statistical approach for computing factors of safety (i.e. numerical measures of mechanical reliability) for any load bearing structure, like a vertical plant stem, is here extended to cope with organic structures whose morphological or mechanical properties have Weibull frequency distributions. This approach is illustrated using the actual length L and critical buckling length L cr of flower stalks (peduncles) collected from isogenic garlic (Allium sativum) populations grown under windy field and protected glasshouse conditions. Our analyses of the data indicate that L and L cr of peduncles harvested from both populations have Weibull frequency distributions, that the factor of safety for glasshouse grown peduncles is very near unity (i.e. S = 1.03), and that the factor of safety of field grown peduncles is 73% higher than that of glasshouse grown plants (i.e. S = 1.73). Comparisons between the S-values computed on the basis of our formulas and on the basis of the quotient of the mean values of L cr and L for each of the two populations indicate that the statistical method gives biologically realistic S-values and that the difference in the S-values for stems grown under protected and unprotected environmental conditions likely reflects the effects of chronic mechanical perturbation (due to wind-induced drag) on normal stem growth and development.