Over utilization of medicinal plants from wild habitat is causing genetic diversity loss of these valuable plants. In order to determine the optimum planting date and density of oregano for successful production, a field experiment was conducted at the Faculty of Agriculture, Urmia University, Iran. The experimental design was split-plot based on randomized complete blocks with three planting dates (April 19, May 5 and May 20) as main plots and four plant densities (8.33, 10, 12.5 and 16.67 plants m-2) were assigned as sub-plots, all of which replicated three times. Results showed that planting date had significant effects on all traits except the stem proportion and 1000 seed weight. The highest values for all traits were obtained from the first date of planting, whereas values decreased with later planting dates. Also, stem number, plant spread, fresh and dry herb yield, seed yield and essential oil yield significantly influenced by plant density. With increase in plant density, stem number in per plant and plant spread decreased. The maximum fresh and dry herb yield (10618.23 and 2934.36 kg ha-1, respectively) and essential oil yield (42.786 kg ha-1) were obtained at the highest plant density. In conclusion, first planting date with higher plant density caused the greater essential oil yield, fresh and dry herb yield.

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