Sometimes you’ll see water droplets form on the edge, tip, or the underside of leaves. This is not dew, which tends to occur mostly outdoors when the air is humid and the night cools off considerably. Dew comes from water condensing from the air and tends to form fairly evenly on the leaf’s upper surface. The drops discussed here come from inside the leaf and are more evident when the air is relatively dry. The formation of such droplets is called guttation.
What is Guttation?
Guttation occurs when the soil is too wet. Too much water penetrates the plant through its roots and this can create pressure that forces the moisture to exude from the plant in the form of droplets. Guttation doesn’t occur during the day, because the leaf’s stomata are open at that time and are able discharge any excess moisture in the form of vapor. It’s when the stomata close down at night and water pressure begins to build up that guttation occurs. You’ll therefore most likely notice it when the sun comes up in the morning, before the drops evaporate.
Outdoors and In
Not all plant guttate. Grasses, though, are well-known for this phenomenon, which is mostly readily seen outdoors. Among houseplants, water droplets on the leaf tips or edges are most commonly seen in aroids (dieffenbachias, philodendron, monsteras, alocasias, etc.) and bananas, while plants in the grape family (Vitaceae, like cissus (Cissus spp.), chestnut vine (Tetrastigma voinerianum) and leea (Leea guinensis) tend to form droplets from the veins on the underside of their leaves. You may also see a drop appear on the underside of the leaf of some figs (Ficus spp.), where it joins the petiole.
Guttation causes absolutely no damage to the plant. At worst, as the drop dries, it may leave behind a smidgen of white deposit (coming from minerals and sugars exuded along with the water) or dried sap. In nature, bees often seek out these drops for the sugar they contain.
Although guttation is harmless, it may however indicate a problem with the way you care for your plants. If you regularly see guttation, it’s possibly because you water too generously. Always apply the Golden Rule of Watering – let the soil dry out before watering again, then water thoroughly – and then guttation will cease. Also, if you water in the morning, there will be less risk of guttation that if you water in the evening, as any excess moisture in the soil will have had time to be absorbed or to evaporate before the stomata shut down for the night.
This text was first published on this blog on November 23, 2015. It has been revised and the layout updated.