The other morning as we sat at the breakfast table at my mom’s, we noticed that the leaves of her two pothos plants had water droplets at the tips of most of the leaves. The plants were sitting on the windowsill in the bay window. Mom noticed it first and remarked about it.
It reminded me of a question that was e-mailed to me a few years ago inquiring about this very same phenomenon.
I have recently bought a wonderful plant called weeping Aglaonema and have noticed that it’s producing water droplets at the tips of the leaves. I do not mist it and always water at the base of the plant. There are no sprinklers or water sources anywhere close to it. I know that these plants are supposed to be super good for cleaning the air and I was curious if this was a property of that.
Guttation causes a drop of water to form
at the tip of a pothos leaf
This is actually the result of a rather interesting event that occurs in some plant species. The appearance of water droplets at the tips and edges of the leaves of a plant is caused by a secretory process called guttation. It often occurs under conditions of moist soil, high humidity, and relatively cool air and it usually occurs in the early morning. The morning we noticed it on Mom’s pothos happened to be a relatively cool morning but rather humid as there was a light rain falling.
Here’s what happens.
There are tiny pores called stomata on the surface of a leaf. In most plant species, these pores are predominately found on the lower leaf surface. The stomata are important for the movement of gasses (carbon dioxide and oxygen) and water vapor into and out of the leaf and they are open or closed depending upon the environmental conditions. When the stomata are open, usually during the day when it is light out and photosynthesis is occurring, water leaves the plant as water vapor through the stomatal pores. This process of water loss through the leaves is called transpiration.
Water droplets forced from hydathodes
on a blade of grass.
The stomata are typically closed when it’s dark, so transpiration is all but stopped at night. Since the roots continue to take up water during the night, pressure (called root pressure) builds up in the leaves and forces water out of special structures called hydathodes which are found along the leaf margins. This is called guttation and is what produces the water droplets that you sometimes see along the margins of leaves in the early morning.
The process of guttation is more common in some plant species such as strawberries, lady’s mantle, and many other perennials and annuals including pothos and Aglaonema apparently. It is frequently seen on grass in the morning and is often confused with morning dew.
So that’s your botany lesson for the day!
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