Guttation mostly occurs on leaf tips or edges. Photo: missouribotanicalgarden.org
Sometimes you’ll see tiny drops of sap form on the edge, tip, or the underside of leaves. It isn’t dew, which tends to occur mostly outdoors when the air is humid and the night is cool. Dew comes from water condensing from the air and tends to form fairly evenly on the leaf’s upper surface.
The drops discussed here aren’t pure water, but rather sap, and come from inside the leaf. They’re also more evident when the air is relatively dry. The formation of such droplets is called guttation.
Guttation isn’t a true disease, but rather a physiological disorder, and is not transmittable from one plant to another.
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 excess to exude from the plant in the form of droplets of sap. Guttation doesn’t occur during the day, because the leaf’s stomata are open at that time and are able to discharge any excess moisture in the form of vapor. It’s when the stomata close 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.
Indoors and Out
Not all plant guttate. Grasses, though, are well known for this phenomenon, where a drop of sap forms at the leaf tip, which is mostly readily seen outdoors. Other plants that frequently guttate are strawberries (Fragaria spp.), ivy geraniums (Pelargonium peltatum) and roses (Rosa spp.), plus just about any plant in the grape family (Vitaceae): grapes (Vitis spp.), Virginia creeper (Parthenocissus quinquefolia), Boston ivy (P. tricuspidata), etc.
Among houseplants, water droplets on the leaf tips or edges are most commonly seen in aroids (dieffenbachias, philodendron, monsteras, alocasias, etc.), passionflowers and bananas and again, plants in the grape family like cissus (Cissus spp.), chestnut vine (Tetrastigma voinerianum) and leea (Leea guinensis). You may also see a drop appear on some figs (Ficus spp.) and hibiscus (Hibiscus rosa-sinensis) where the petiole joins the leaf blade.
Guttation can affect succulents, too, including crassulas and echeverias. On succulents that have no leaves, like cactus, it may appear on their stems.
Guttation causes is not generally harmful to the plant. At worst, as the drop of sap dries, it may leave behind a white deposit (coming from minerals and sugars exuded along with the water) or a particle of dried black sap. In nature, bees often seek out these drops for the sugar they contain.
If the plant remains sitting in waterlogged soil, though, it could actually cause certain cells not just to leak sap, but to burst and die, leaving a corky growth called edema. It’s unsightly, but not really harmful to the plant … and unless the damage occurs over and over, killing too many cells, in which case the leaf may be of little use to the plant, so it will shed it.
Although guttation in itself 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 or something is keeping the soil’s moisture from draining away. 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.
Guttation: just one of the strange things plants sometimes do.
Adapted from an article originally published on November 23, 2015.