At some point, you may see water droplets forming on the tip of your plants’ leaves. This makes the plant look like they are crying or dripping water. Some plant owners believe that this is dew, but this is generally not the case for indoor plants. If you see your plant “crying,” it is highly likely that you are observing guttation.
Guttation is a normal process that occurs when high root pressure pushes water droplets through special leaf pores called hydathodes. In general, guttation does not indicate any problems with your plant. However, in some cases, the mineral content of the guttation fluid can burn the tips of the leaves.
The rest of this article will describe the phenomenon of guttation in further detail and will discuss some of the scientific studies that have investigated the impacts of guttation to plant health.
What is Guttation?
As previously discussed, guttation occurs when high root pressure pushes fluid (xylem sap) through special leaf pores known as hydathodes. This happens when conditions are conducive for rapid root absorption but not for transpiration. In laboratory settings, scientists will artificially create this type of environment by placing a potted plant with saturated soil under a bell jar. Within a short period of time, guttation occurs.
It is important to note that a similar “crying” or “bleeding” effect can occur due to pressures caused by stems (Kramer, 1949). However, guttation refers to fluid excreted specifically because of root activity.
Guttation is common among many species of low-growing herbaceous species and succulents. Some trees will exhibit guttation, but this only occurs under special circumstances (Stocking, 1967).
On cool spring nights following warm days, you will frequently see guttation on outdoor plants. This is because, under these conditions, the soil temperature is significantly warmer than the air, and the air tends to be quite humid. As a result, the rate of transpiration is reduced while the amount of root activity has increased due to warmer soil temperatures (Gaumann, 1938).
You may also see guttation on your indoor plants in the early morning. This is because guttation occurs at night when the rate of transpiration is considerably lower than during the day for most plants.
The following video is a time lapse that shows guttation occurring on Colocasia leaves.
Transpiration
Transpiration describes the evaporation of water from the stomata of plant leaves. This process is important because the pressure from transpiration, also known as the transpiration pull, is the force that allows water to move from the soil to the leaves and stems of the plant.
The transpiration pull is explained by the Cohesion–Adhesion Theory, with the water pressure difference (also known as water potential gradient) in the leaves and the atmosphere providing the driving force for water movement. The water potential of the atmosphere depends on the relative humidity and temperature of the air, and typically ranges between –10 and –200 MPa. Leaf water potential typically ranges from –0.2 to –3.0 MPa. Water evaporates from the leaf due to this large difference in water pressure (Lopez and Barclay, 2017).
Although transpiration and guttation both occur due to pressure differences, they are not the same thing. Guttation and transpiration are processes that take place in different parts of the leaf/plant. In addition, transpiration is a regulated process while guttation is not.
Hydathodes
As mentioned previously, hydathodes are special leaf pores. Specifically, hydathodes are structures containing water pores located at leaf margins (Cook et al., 1952). They connect to the xylem vascular system, which is responsible for transporting fluid throughout the plant. These structures are typically found in herbaceous plants and aquatic plants.
Hydathodes are important plant structures because they act as water safety valves.
Composition of Guttation Fluid
Guttation fluid is comprised of a variety of organic and inorganic compounds. This is because guttation fluid is basically an overflow of the soil water flowing through the plant. As such, the fluid will contain many of the nutrients that the plants will use.
The composition of guttation fluid also depends on the soil fertility and the plant itself. If your soil contains excess nitrogen, the guttation fluid can actually burn the leaf tips.
A study conducted by researchers at Michigan State University investigated the composition of guttation fluid exuded by barley, rye, and wheat seedlings. They found that the total sugar content of the guttation fluid from the rye and barley were about equal. However, the total sugar content was lower in wheat. Similarly, they found that sugar was the principal sugar component of rye and barley while galactose was the principal sugar component of wheat. The concentration of most inorganic compounds was highest in rye and lowest in wheat (Goatley and Lewis, 1965).
Interestingly, scientists can also determine the amount of insecticide/fungicide/weedicide residues present in the plant by analyzing the chemical composition of guttation fluid (Harris, 1999). This type of analysis is important because it helps researchers understand how such chemicals impact pollinators such as honeybees.
Guttation vs. Dew
Some plant growers confuse guttation with dew. Although they may look similar, dew and guttation are not the same thing. Dew occurs when water from the atmosphere condenses on the surface of the plant leaves. In contrast, guttation is fluid that comes from the plant itself.
You can often tell the difference between guttation and dew if you look at the plant carefully. You will often see dew covering most of the leaf surface. However, guttation fluid is typically found on the tips or edges of a leaf.
Is Guttation Bad For Plants?
Guttation is common after watering and is typically not a problem. However, if your soil has a high mineral content, a white crust may form after the water evaporates and cause leaf burn (Ivanoff, 1963). Some studies also show that guttation can damage the hydathodes and allow harmful microorganisms to infect the plant. To avoid these issues, simply rinse off the leaves with fresh water.
Continuous “crying” may also indicate that you are overwatering your plant. If your plant starts crying more frequently than usual, check the soil moisture before watering and watch for other signs of overwatering.