Marigold (Calendula officinalis L.) belongs to the oldest medicinal plants which had been used for the pharmaceutical industries from the ancient times. In order to evaluate the impacts of different plant densities on growth and flower and seed yield of marigold, a field experiment was performed based on randomized complete block design with four replications at the Agricultural Research Station, Azad University of Torbat-e-Jam, during growing season of 2008-2009. Four plant densities included 20, 30, 40 and 60 plants.m-2. Flowers were harvested at three stages. Seeds were collected at the end of growing season. Harvest index (HI) calculated based on the ratio between flower yield and biomass yield of marigold. The results indicated that the effect of plant density was significant (p≥0.01) on seed yield, flower yield, biological yield and HI of marigold. By increasing plant density from 20 to 60 plants.m-2, biomass yield enhanced up to 100%. Whereas, by increasing plant density up to 40 plant.m-2, seed yield and flower yield declined afterwards.

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