Meteorological indices viz. growing degree days (GDD), helio thermal unit (HTU), and photo-thermal unit (PTU) based on air temperature are used to describe changes in phenological behavior and growth parameters. Plants have a definite heat requirement before they attain certain phenophases. A change in temperature during phenophases of a crop adversely affects the initiation and duration of different phenophases and finally the economic yield. Among the different management factors, sowing time plays a key role in obtaining higher yield. The objective of this study was undertaken to find out the optimum sowing window and the amount of heat units required to change their phonological development for groundnut variety VRI 2. A field experiment was conducted at experimental farm of Agricultural College and Research Institute, Eachangkottai during Margazhi pattam 2019 and 2020. The experiment was conducted in Randomized Block Design with four replication. Different morphological indices were observed like plant height, number of branches, dry matter and number of pods and yield attributes and yield of groundnut VRI-2 was recorded. The heat unit concept of Growing Degree Days also worked out for individual sowing windows. Among the sowing dates, Fifth January, recorded essential GDD of 1651.3°C and higher growth attributes, yield attributes and yield of groundnut (2370 kg ha-1).