So you woke up and found this weird water droplet seemingly drooling from your plant. What is it, and should you worry?
Nope.
This is actually an amazing part of plant physiology called guttation. Basically, this is one of the two ways many healthy plants expel excess water that the roots drank up. Plants are living things that need water to live. They absorb water, mainly through the roots, and then that moisture and any nutrients picked up there are distributed through the rest of the plant. Xylem and phloem are the two main transport tissues in vascular plants that contribute to this. The xylem moves the water and nutrients from the roots and soil upward into the rest of the plant. Photosynthesis (light used to generate energy for the plant) generally occurs in the plant's leaves, the energy or food created in the leaves is transported downward through the plant via phloem.
Xylem has to fight gravity in order to move through the plant from the roots. This is done through a process called transpiration, which is the "exhalation of water vapor through the stomata". Transpiration is the other way that plants expell excess water. The stomata is essentially how the plant breathes through its leaves, they open up and are more active during the day. At night, the stomata close, but the xylem still needs to flow to keep the leaves from wilting which causes transpiration to slow; the roots allow minerals to build up so this can occur. The mineral build-up encourages water to the plant's roots, which creates pressure in the root cells. The pressure pushes xylem back up to the leaves.
Leaves actually only utilize a certain amount of water, usually less than the roots take up. Plants generally only metabolize about 3% of the water the roots absorb. The remaining water is expelled from the plant via transpiration and guttation.
During the day or in dry conditions, the extra water evaporates due to the sun or wind. At night, cooler temperatures, calm conditions and closed stomata mean the leaves don't lose as much moisture as during the day. When the pressure in the root cells pushes water-carrying xylem up, the pressure forces excess water out of the leaves through special structures called hydathodes located at the tip and margins or leaves. Guttation mainly occurs at night, but it can happen during the day in areas with high humidity.
Plants and Guttation
Guttation doesn't happen in every plant. Trees, for example, are too large to create the force needed to push xylem upward hard enough to cause guttation. Plants that most commonly experience guttation are non-woody and smaller than 3 feet tall, but some shrubs and vines show guttation as well. Guttation is typically not a problem for plants unless your soil has a high mineral content. Once the water does evaporate, the minerals get left behind and can burn the tips of the leaves. Reducing the amount of fertilizer you use can prevent this burn.
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