A field experiment was conducted with dragonhead to evaluate the effects of iron nano-fertilizer rates (0, 1, 2 and 3 g l -1) and planting density levels (10, 15, 20 and 40 cm) on the fresh herb, essential oil content and other traits under the natural conditions. Traits such as number of flowering branches (NFB), height of first flowering branch (HFB), number of secondary branches (NSB), stem diameter (SD), essential oil content (EOC), dry mass (DM), essential oil yield (EOY), total anthocyanins (TA), chlorophyll a (CA), chlorophyll b (CB), flavonoid 270 nm (F270), flavonoid 300 nm (F300), and total flavonoid (TF) were measured. Results showed that the nano Fe treatment × trait (TT) biplot accounted 39 % and 25 % of total variation, respectively. The vertex treatments in polygon biplot were D2-N2 (15 cm density and 1 g l-1 nano-fertilizer) was the best in the EOC, DM and EOY, while D4-N3 (40 cm density and 2 g l-1 nanofertilizer) was the best for TA, F270, F300 and TF. Sowing densities (10, 15 and 20 cm) with iron nano-fertilizer treatments (1 and 2 g l-1) were the best combinations of evaluated factors for all the measured traits of the dragonhead.
