Yaupon holly (Ilex vomitoria Ait.) is the only native American source of caffeinated tea and the small amounts of tea product that is available is currently wild-collected from diverse populations. A clonal field plantation of yaupon was grown under shading and fertilizer treatments and harvested three times in one season to observe changes in yield and phytochemistry. The June and September harvest produced more mass than the July harvest for all treatments. Shading and fertility had interactive effects on increasing fresh mass of the pooled annual harvest, whereas the providing 30% shade and increased fertilizer application (from 567 to 1163 mg/N plant) raised yield 58%. Fertility of 1163 mg/N per plant with 60% shade increased yield another 13% to approximately 1070 kg/ha. This experimental plantation contained 467 plants per ha and was at about half the density of commercial fields (882 plants per ha). Leaves were smaller in July and larger in June and September. Shade greatly increased the leaf size and water content. Caffeine content increased with leaf size over the duration of the experimental treatments and 60% shade treatments in September produced the highest caffeine content (1.21 ± 0.17% of dry mass). In general alkaloids were promoted by shading, and phenylpropanoids were promoted by bright light. This report from one season of observation showed that genetically uniform yaupon holly plantations were manipulated for yield and quality using shade and fertilizer
