Withania somnifera (Dunal), a medicinally important plant, is extensively used in traditional Indian herbal preparations as well as for modern nutraceutical and functional food supplements. Its characteristic phytogenic molecules are modified steroidal lactones called withanolides. Withaferin A is a predominant constituent and is pharmacologically active. Here, we studied the dynamics of biogenesis and accumulation of withaferin A and withanone in Withania leaves at various developmental phases (very young, young, mature, and senescent). HPLC analysis was conducted to determine the amassed quantities of these phytochemicals, while their de novo biosynthesizing capacity was examined via incorporation studies with a radiolabeled primary precursor, $[2-^{14}C]-acetate$. De novo biogenesis and accumulation of withanolides was most active in young leaves. Here, we also discuss developmental patterns and secondary metabolism in relation to eco-physiology and phytopharmaceutical variability.