The effect of photoperiod and growing degree days (GDD) on dry matter and dry matter partitioning in Jerusalem artichoke was investigated during 2008-09 and 2009-10. Three Jerusalem artichoke genotypes (CN-52867, JA-89 and HEL-65) were planted in 15 day-intervals between with thirteen different dates (September 20 to March 20) at Khon Kaen University, Thailand. Jerusalem artichoke genotypes responded differently to varying planting dates for harvest index, shoot dry weight, leaf area, number of tubers and tuber size. Two genotypes, CN-52867 and JA-89, were significantly more productive on the planting date of 20 September and they also performed well on planting dates of 5 October to 20 March. Plant grown in long photoperiod with a higher number of GDD produced shoot dry weight rather than greater number of harvestable tubers, while short photoperiod induced high partitioning of assimilates to harvestable tubers. Jerusalem artichoke plants grown during short photoperiod were smaller and produced larger tubers than those grown during long photoperiod. Tuber yield was relatively unchanged across planting dates. Since Jerusalem artichoke during short photoperiod had smaller plants, growing Jerusalem artichoke at higher plant population with optimum density is highly recommended to increase tuber yield. The information obtained in this study is extremely important for Jerusalem artichoke production and breeding in the tropical agro-climatic conditions such as Thailand.