An experiment was undertaken to determine the herbage biomass and oil production of thyme (Thymus vulgaris Linn.) and hyssop (Hyssopus officinalis Linn.) in 2003 and 2004 in the semi-arid region of Khorasan in Iran. The experiment was a split plot with three irrigation intervals as main plots and three planting densities as subplots, all of which replicated three times. Irrigation intervals consisted of 7, 14, and 21 days for both crops and planting densities of 6.6, 8, and 10 (plantsm−2) for thyme and 5, 6.6, and 8 (plantsm−2) for hyssop. Different planting densitieswere employed by changing planting distances on cultivation rows. Herbage biomass and oil production of shoots, harvested at flowering were measured as annual production of each crop. Irrigation intervals did not change total harvested herbage biomass and oil production of both crops. Averaged across both years of the experiment, thyme produced higher oil than hyssop. Both crops produced higher biomass and oil in the second year of the experiment compared to the first year. While thyme plants biomass and oil production were lower at the highest planting density, hyssop plants showed no response to planting density. Herbage biomass and oil production of hyssop did not show a clear trend in response to interaction of irrigation intervals and planting densities in both years of the experiment. Our results showed that there is a high potential for saving water through longer irrigation intervals (e.g. 14 days) using locally adapted plants in the semi-arid conditions of Khorasan. These crops serve as alternative sources of income in dry years.

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