Rain is great for the grass, because just like humans and everything else, grass needs water to function. However, it also needs nutrients like nitrogen for photosynthesis to occur. Grass and plant roots cannot just absorb nitrogen as it is. Instead, the nitrogen atoms need to be broken up. Most commonly, micro-organisms in the ground have to conduct this process, but lightning can do it as well.

Here's how it works! Lightning strikes are so strong that they can break up the nitrogen atoms in the air, and then those nitrogen atoms attach to oxygen atoms. Together, they go through the process of dissolving into rain and turning into nitrates. Those nitrates rain down into the soil and are all ready to be absorbed by the grass roots. This is a quicker process and by the end of a round of lightning storms, the grass will sometimes be noticeably greener.