Those unexpected drops of water on your plant leaves

Bob Dluzen
The Detroit News

The other evening, I was sitting in the living room reading when I glanced at a bird flying past the window and noticed water drops on the leaves of our Monstera deliciosa plant. 

This phenomenon, called guttation, happens fairly often and is a normal part of a plant’s inner workings. 

Guttation drops forming on an indoor Monstera houseplant. Also notice the drip tips on each lobe of the leaf.

Oozing sap usually occurs when a plant is injured as a result of a cut, tear or other trauma. But in the case of guttation, no injury or damage has occurred. 

The drops are more than just plain water, they are actually drops of plant sap that contain all of the substances found in sap including minerals, sugars, proteins and other compounds. 

Guttation takes place only at the leaf margins through small water pores called hydathodes. They are part of the plant’s piping system that includes the xylem.

The xylem carries water and sap through the plant starting at the roots, through the stems and leaves and finally terminating with the hydathodes located all along the leaf margins.

It’s not just houseplants that guttate, many other plant species, both herbaceous and woody,  do it to a lesser or greater degree. Some common examples of plants that easily guttate include turf grass, squash, corn, field crops and other farm and garden plants. 

Guttation is more likely to happen when the soil is fertile and contains an abundance of water. 

It is also more likely to occur at night when the rate of transpiration slows down or stops. Under those conditions, a positive pressure is built up in the roots that moves the sap upward through the xylem and out of the hydathodes. It is a way of removing extra, unneeded water from the plant. 

Some species of plants, like corn, for example, will guttate during the day as well as at night. 

I remember as a child standing in my grandfather’s cornfield on a hot, humid August afternoon with the corn plants towering over me as I marveled at the way the corn leaves were “sweating.”

Some plant species use guttation to remove excessive levels of minerals that would otherwise build up to a toxic level inside the plant. Under those conditions, guttation carries the high concentration of dissolved minerals out of the plant where it collects in the drops and eventually falls to the ground or is washed off by rain. 

Some tropical plants such as Monstera have “drip tips,”, pointed structures on their leaves that encourage liquids to drip from the plant more quickly. 

In some plants such as lettuce, guttation never results in actual drops. Instead, the liquid spreads out across the leaf surface and runs down to puddle in the leaf whorls. That's why you sometimes find water in a head of lettuce even though there was no rain or irrigation or other apparent source of water. 

With other plant species, guttation drops will form on the leaves, then when conditions change and before they can evaporate, the drops are sucked back into the plant. It’s a fascinating process.

It might be fun to watch your plants closely this summer and see if you notice guttation drops forming, and under what conditions it’s happening.

This is another example of the complicated and fascinating world of plants and nature.