Some people go outside early in the morning, because they are either weird early birds or have to because of their job. Everyone has seen a plant–probably grass in some nearby yard–in the early morning though. Those plants are also almost always wet. So why are plants wet in the morning? Also, a moment for everyone who is not an early bird but still has to get up super early.
Oh and uh… it’s also not the song.
It’s Just Water
If you thought dew was weird like, plant juice, or something that’s unfortunately not the case. Dew is actually just the water that’s in the air around you, and formed when it condenses around a plant.
The reason dew typically forms just during dawn or evening is just because that’s when it’s typically pretty cool, and it hasn’t gotten warm enough for the water to evaporate away. It’s typically then that the ambient temperature drops below the dew point–which is the temperature at which the air must be cooled before it can be saturated with water vapor. The more humid it is, the higher the dew point is. Once the temperature drops below the dew point, the amount of moisture that can be in the air goes down. Since it can’t be in the air, the water vapor becomes liquid and condenses onto a relatively cold surface.
Some of you are probably sitting there thinking this is the exact same thing that happens when the outside of a glass gets wet seemingly spontaneously. That’s because the process by which dew forms is exactly the same. Like your glass windows, plants are poor thermal conductors and don’t heat back up as quickly when they’re cooled. This puts them in a position to be relatively cooler than the ambient air–allowing water vapor to condense.
What About Indoors? Are My Plants Sweating?
That’s not very exciting, and you’re probably now wondering about indoor plants. The inside of your house is probably a lot less humid than the outside (most of the time), and indoor houseplants can still be wet in the morning. You might be asking if your plants are sweating–which short answer they’re not because they can’t, but they kind of can.
Two things drive this process, one of which is transpiration. This is how water goes through a plant, from the roots up. Leaves all have these little pores in them, and these powers allow plants to exploit water potential to move water through them. The central principle is that water potential wants to be at equilibrium between two systems, where the plant is one system and the ambient air around it (aka the rest of the world) is another. Water potential generally wants to be equal between them. It’s like when you have a balloon, and then puncture it. Air comes out because pressure within the balloon is higher than the air around it.
Anyway, when the water potential in the air is lower than that of the plant, water moves from the plant outside–exiting through the pores on the leaves (they’re called stoma, by the way). This, very simplistically, pulls the water in the plant up through it from the roots.
There’s also guttation, which is closer to plant juice. Guttation is when sap from the plant forms at the edges of a plant’s leaves. It also happens at night when transpiration doesn’t normally occur. When there’s a lot of moisture in the soil, the roots will continue to absorb water, and water just accumulates in the plant. Eventually, this forces some water out and you get little droplets.
Speaking of plants, see if you know the parts of them we eat often here.