The yield that can be obtained from drug plants in different localities will naturally vary according to the suitability of the situation for the plants selected for cultivation. Even in the same locality wide variations in yield will result from differences in the lay of the land and in soil, drainage, and seasonal conditions. The skill of the grower and the degree of care and attention which he bestows upon his crop are also factors affecting yield.

Many of the drug plants mentioned in this bulletin have not been grown on a scale large enough to give a very satisfactory basis for calculating yields. Acreage yields calculated from the product of small garden plats are generally untrustworthy, since in such plats the plants are usually more favorably situated with respect to soil and are given better culture than when under field conditions. Moreover, as the area increases, it becomes more difficult to maintain an approximately perfect stand and to protect the crop from the ravages of insects or other destructive agencies. The returns from small experimental areas can at most be regarded as only an indication of the yield that may be expected under favorable conditions, and the prospective grower will do well to proceed cautiously until he has determined for himself the possibilities of yield in his particular location.