At night...
It is so interesting, I was in the kitchen washing dishes when I noticed our seedlings folded up all their leaves. Are they sleeping? Yes, plants do sleep at night. They can not make food, so they shut down by closing their stomata.
Let me talk a little bit of science here:
Green plants are the only plants that produce oxygen and make food, which is called photosynthesis. Photosynthesis means "putting together with light." This takes place in sunlight. From sunlight, green plants combine carbon dioxide and water to make sugar and oxygen. Green plants use sugar to make starch, fats, and proteins. there are tiny pores called stomata. Oxygen and carbon dioxide enter and leave through the stomata.
