Plants as autotrophs are primarily limited by light availability and ambient temperature. These two major factors limit plant resources and its ability to invest energy to various competing functions. Plant growth and phenology could be quantitatively modelled as a function of accumulation of energy from light over time at favourable ambient temperature. Historically, effects of temperature on plants has been calculated using a measure of mean temperature or of degree days. However, these methods fail to take into consideration the effects of changing day length and daylight temperature. This novel approach takes into account that in general, daylight heat promotes photosynthetic activity, and night heat accumulation affect losses due to cellular respiration. Our study examines the consequences of daylight and night time heat accumulation of selected species. In our study of Cucurbits, logistic regression indicates that out of many meteorological factors that day length and mean hourly temperature  account for 93 % of variation in timing plant growth and phenology. Mathematical models incorporating daylight and night heat accumulation may be used to quantify plant resource accumulation and timing of plant phenology. This may help to redefine the biome and allow to model ecosystem distribution. Also, heat accumulation models may better account for climate change effects from the perspective of plants, and assist environmental managers in better prediction of plant phenological stages, for example in agricultural applications.