Matching the phenology of the crop to the duration of favorable conditions by selecting the most appropriate sowing dates to avoid periods of stress is crucial for maximum yield. A 2-year field study was conducted to assess the effects of climatic factors on groundnut growth and yield at various dates of sowing in a Mediterranean-type environment at Hatay, Turkey in 2001 and 2002. Two cultivars (NC 7 and Com) were sown at five sowing dates (15 April, 1 May, 15 May, 1 June and 15 June) to expose the groundnut plant to a variety of climatic conditions, and were harvested at 120, 140 or 160 days after emergence. Sowing dates, cultivars and growth durations significantly affected to pod yield, number of pod per plant, shelling percentage, 100-seed weight, biomass, harvest index, crop growth rate, and oil and protein content. Very early sowing before I May did not generate any advantage for earliness and yield due to sub-optimal temperature for vegetative growth. Our results revealed that the most suitable period for groundnut sowing is between mid-May and early June for the eastern Mediterranean region since plants expose to suitable temperature regimes during the vegetative and the reproductive growth stages, and receive more solar radiation and sunshine duration during the entire growing period. Lengthening of growth duration had positive effect on yield at early sowings, but satisfactory yield level can be achieved with 140 days growth duration using current cultivars. It is also possible to obtain over 3.0 t ha(-1) pod yield, which is considered as acceptable level by the grower in the region with shorter growth duration in double crop production. It was concluded that Mediterranean climate offers a long and suitable environment having at least 160 calendar days or 2400-2500 degrees Cd thermal time for both main and double crop production of the groundnut with acceptable yield levels. (c) 2007 Elsevier B.V. All rights reserved.