effect of planting date on yield and yield components of silybum marianum under golestan climatic conditions

background and objectives: milk thistle (silybum marianum), a medicinal plant of the asteraceae family that have been used long time ago, in the treatment of liver disease. sowing date of this plant has not been determined, therefore, this study was necessary. this plant was identified as a weed, this plant is identified as a weed, while silymarin in the seeds are used in the anti-hepatitis and it is an important medicinal plant today. silymarin, derived from the milk thistle plant, silybum marianum, has been used for centuries as a natural remedy for diseases of the liver. the aim of this study was to determine the suitable sowing date for seed production of milk thistle as a medicinal plant in golestan province.materials and methods in order to determine the effect of sowing date on seed yield of silybum marianum as a medicinal plant, two experiments were carried out based on a randomized complete block design with four replications in the experimental field of plant production college of agricultural and natural resources of gorgan university and a farmer field in aliabad. to record of different stages of development were selected 10 plants in each plot. seed yield was measured after ripening with capitol harvesting. capitol number per plant, number of seeds in the capitol, plant height at harvest, sowing to harvesting time and 1000 seed weight were measured at each location. analysis of variance was done using combined analysis method and mean comparisons were made along with slicing when interactions were significant. five different sowing dates were considered from 2 oct. to 31 dec. with 30-day intervals and a separate sowing date on 24 february in both sites. resultsresults showed that measured traits were significantly affected by sowing dates. site effect was significantly influenced head number per plant, seed number per head, days to the flowering, to harvesting and seed yield. also, results revealed that interacted effect of sowing date × site was significant on heads number per plant, seed number per heads, days to the flowering time and to harvesting, seed yield at 1% probability level and plant height at 5% probability level. the regression results showed that 93% of seed yield is dependent to heads per plant and number of seeds per head. the highest average seed yield in gorgan and aliabad was recorded 1634.9 kg h-1 and 1920.2 kg h-1 respectively. conclusionresults suggested that milk thistle as a medicinal plant could be successfully grown on 1 nov. as the best sowing time under gorgan and aliabad climatic conditions in the golestan province.