The ideal temperature depends from plant to plant. However when you talk about the marijuana plant, it grows well when the temperatures are around 68-77F (20-25C). Growers who grow their weed in these temperatures have seen the maximum yields and flowers. Growers who go too hot or too cold tend to suffer as their plants might get damaged. However, this is not a hard and fast rule and you can go to 15C/32C and that won’t be counterproductive either. However, this is the best possible range for growing weed.