Guttation is the expelling of excess water or nutrients through tiny openings on leaves and stems.
This biological process enables plants to restore balance to their nutrient and water content.
Key facts about guttation
Name – guttation
Common name – crying plant,
weeping leaves, teary plant
Type – plant physiological process
Occurence – often
Observation time – early morning
Affects – houseplants & low-lying plants
What is guttation?
Guttation occurs when a plant oozes water and minerals out from perfectly healthy leaves, stems, and sometimes even flower petals.
It takes place when roots of a plant absorb more water than the plant actually needs.
Tiny, specialized cells on the surface of a leaf or stem are connected to veins and sap channels of the plant. This cluster of cells works as a nozzle. It releases water from the plant’s vascular system to the outside, forming drops that look like dewdrops.
This process where excess pressure is released from inside the plant is called guttation.
- These nozzle-like cells are called hydathodes. They’re a special class of stomata. Stomata are bean-shaped cells that open up to let the plant breathe and transpire.
- Hydathodes are usually placed around the rim or tips of leaves, on the leaf surface, or at junctures between leaves and stems.
- Less than 5 % of all water that goes in a plant is released through guttation. Nine tenths is from transpiration, a more powerful phenomenon.
About the term “Guttation”:
- The verb to say this “guttate”, but it isn’t very common. Simply, variations like “guttation is observed” or “hydathodes exude/secrete/release” are used. “Guttant” is the fluid expelled.
- It comes from latin “gutta” which means “drop”. An easy memory trick is to remember words in English like “gutter” and French “goutte” (also “drop”) and go from there.
To understand why plants developed guttation as they evolved, it helps to brush up the following:
- how water is used in a plant.
- techniques plants developed to move this water around, creating pressure.
Hydathode nozzles are one of the biological tools plants use to regulate pressure inside them.
Uses of water in a plant
Water used to transport nutrients up and down the stems and leaves is called sap. But there are more uses of water in a plant than simply transportation! Here is a short list of how a plant uses water:
- Nutrient transport from roots to leaves and vice-versa
- Cells are full of water. On a microscopic level, this is where chemical reactions take place.
- In some plants, water shapes the plant, such as the shy but rugged Mimosa pudica which closes when touched.
- Some seed pods use water to eject seeds: when dry, they burst and project seeds far away. A typical example is the common Geranium.
- On the surprising Ginkgo biloba, water fertilizes the seed: it carries the male pollen to the female ovum inside the hull to fertilize it.
Plants are under pressure
If ever you’ve opened a fresh coconut, you must have noticed that when the hull is slit, drilled or broken, coconut water spurts out. The pressure inside the coconut is higher than the pressure of the air around it. You can also see happen when slitting open a watermelon: the last few inches simply split apart on their own.
Thanks to a combination of chemical reactions, tissue structure and cell components, a plant is able to control water in and around it.
- Starchy stems help Dracaena resist drought. Starch captures water molecules and releases them when the weather is dry.
- Capillarity helps many flowers pull water up from ground level. This is the basis for fun experiments with cut peonies or carnations absorbing dye up to their petals.
Guttation is one of the ways excess pressure is released. If not for this, the plant might burst at weak spots of veins and leaves!
When to find guttation on plants
Night-time and early morning
Plants breathe at night and still need sap to flow up and down the plant. Guttation takes over to force sap and water up when transpiration stops being effective.
- Daytime breathing is powered by transpiration or “sweating”. In warm, dry air, water evaporates from leaves and creates a “vacuum” inside the plant. This vacuum pulls nutrient-rich sap up.
- At nighttime, evaporation and transpiration don’t work as well. The plant compensates by having the roots push water upwards. To do this, roots use chemicals to attract water from the surrounding soil.
- This builds up pressure in the plant and sap and minerals are pushed up. It’s such a strong phenomenon that excess water needs to be released at the tip of leaves through guttation!
Days of high moisture and humidity
When the air is near or above 100% relative humidity, it’s impossible for a plant to sweat.
- Even during daytime, guttation must take over to get sap circulating through the plant.
Excess moisture in the soil
It isn’t a common reaction, but guttation is one way of helping the plant evacuate excess water around roots. It’s a coping the plant uses to protect roots from rotting.
- Some plants use guttation to drain the soil around them like the weeping willow tree which thus is doubly weeping!
- Guttation isn’t necessarily a sign of over-watering.
Seedlings and young plants tend to guttate more than older, more established plants.
Plants that tend to show guttation
Here is a partial list of plants that have been shown to guttate. Have you observed guttation on any of your own plants? What are the crying plants you’ve encountered?
Common guttating plants
Many very common plants tend to guttate when conditions are right. They all share their short height in common: guttation rarely occurs higher than 3 feet (1 meter) above ground. Only a few tree species that love wet soils are very prone to guttating.
- Plants with sawtooth-like leaf edges (serrated leaves) are usually good guttators.
Grasses – almost all types of grasses, from the Pennisetum family to the banana tree, including fescue and bamboo. More often then not, when your lawn is wet in the morning, it’s not dew but guttation.
Houseplants – most types of succulents (Echeveria, Jade tree, Senecio, Kalanchoe…) and a great many houseplants such as Monstera, Dieffenbachia, Ficus, Philodendron, Spathiphyllum, the ZZ plant… Even members of the Dracaena family do it. Orchids also guttate but the hydathode cells are on the leaf surface, not around the edges.
- In tropical regions, a lot of guttation occurs. This is because air moisture is often very high, which makes transpiration difficult. In a jungle, it’s quite common for it to be “raining” from the canopy even though not a cloud is in sight.
- In mangroves, guttation is how the trees return excess salt to the sea.
On a different scale, other organisms that aren’t really plants also exhibit guttation: algae and fungi.
Plants that don’t guttate
Most plants of the citrus family don’t guttate – this makes them more vulnerable to edema.
Taller trees, especially in temperate regions which are cooler and drier than the tropics, don’t guttate much.
Conifers also don’t guttate.
Guttation and plant diseases
Breakthrough research is analyzing the effect of guttation on the spread of plant diseases.
Indeed, when water flows in and out of the plant through those nozzle-like hydathodes, germs are transported in and out, too.
Guttation favors spread of plant disease
A study revealed that in green-house grown tomatoes, bacterial canker responsible for tomato wilt spread because of guttation.
- When plants were handled while guttation was present, they fell sick and disease spread.
Two lessons were learnt from this:
- seemingly healthy plants already had germs and bacteria appearing in guttation drops. As in human diseases, plants could contaminate other plants even as it was still fighting off symptoms of the disease. Plants were contagious through guttation during the incubation phase.
- And second, to protect healthy, uncontaminated plants, it was best to wait for guttation to evaporate before intervening among the plants.
If any plants in your garden are diseased, wait for guttant drops to dry off before working among them.
Note: in the case of lawn diseases, it usually helps to clear guttation and dew from the grass. This ensures it dries faster. Spores from lawn fungus won’t have time to hatch and contaminate new blades of grass. Simply mow the lawn or run a rake or roller across it early every morning.
Plants can defend themselves, too
It’s been shown that special proteins that block germs tend to concentrate around the hydathodes.
These proteins react with bacteria, fungus and viruses and try to destroy them before they enter further into the plant.
A healthy plant, well fertilized and watered, will produce plenty of these “soldier proteins”. A plant weakened by disease, drought, or neglect will tend to have less of these proteins available.
- Interestingly, the composition of guttation fluid can be strongly influenced by compounds floating in the air.
- For example, methyls and ethylene would trigger changes in which proteins appeared in the guttant sap.
This is a fascinating inroad regarding how plants communicate. It may explain why plants not yet diseased start producing chemical defenses as soon as one of their kind is attacked by pests or illness.
Plant care and guttation
For indoor plants
- For indoor plants, there is a risk when too much guttation occurs. It evaporates and leaves white spots on leaves.
- These spots are from minerals that stay behind once water dries up. These form white spots on leaves.
- When minerals accumulate, they start damaging leaf cells, creating leaf burn spots. These spots can be either yellow, brown or black.
To reduce guttation on houseplants, you can do the following:
- avoid watering in the evening.
- water with soft water or rainwater, not mineral-laden hard tap water.
- don’t over-fertilize, since it keeps adding minerals to the soil. Better to repot or topdress a plant instead.
- wipe the spots off gently with a soft moist cloth.
For outdoor plants
- For outdoor plants, the answer is no.
- Rain rinses off any deposits early enough to avoid any damage.
- The only risk is poisoning neighborhood relationships if your tree spatters guttation all over your neighbor’s prize car or favorite sitting bench.
Is guttation dangerous?
For the plant, guttation is a sign of good health.
For us humans, and pets or animals, it’s almost impossible to contract illness, disease, or problems due to guttation.
There is no known allergy to guttation fluid, except in cases where the plant itself induces allergies.
- Poison ivy guttation also causes allergies even if you don’t touch the plant.
Content of guttant (or guttation fluid)
It’s mostly water, but there are a lot of other compounds as well:
- minerals & metals like potassium, calcium, manganese, iron and salt (sodium)
- sugars like glucose, galactose
- nutrients and amino acids
- viruses, bacteria, fungi (dormant and active), depending on the host plant
- microscopic cell debris from nearby wounds on the plant
- proteins and compounds the plant uses to defend itself (antibacterial and antiviral)
- toxins and contaminants the plant seeks to expel
It varies greatly depending on the plant, growth stage, soil, weather, season, temperature, etc.
- Nutrient-dense and micro-organism-filled guttant explains why it’s best to harvest weeds at that time to prepare fermented weed tea. It’s a natural way to control diseases, pests, and fertilize.
Guttation and bees
Bees and many insects, however, rely on guttation to drink. This is particularly dangerous for them when the plants they drink from have been sprayed with pesticides and insecticides.
- Chemicals, even when washed off of leaves into the soil, are pumped back up through the plant and appear in guttation drops.
- Sometimes, when just the seeds were coated with fungus and insect deterrents, those chemicals still appear in guttation droplets.
- Bees that drink from these contaminated drops can die in minutes.
- In extreme cases, entire bee colonies can die off. This is one possible explanation of Colony Collapse disorder.
This proves how important it is to always refrain from using chemicals. It’s far better to use natural, home-made fertilizer and pest control instead.
- Guttation actually increases the effect of organic “Bordeaux mixture” treatments since it concentrates copper around leaf edges. This is where pests take their first bites…
Plant mechanisms similar to guttation
- Gummosis is mostly mentioned when a disease like canker triggers too much fluid release.
- But it is also a perfectly natural phenomenon that also occurs in healthy plants.
- When the environment changes too drastically, gummosis occurs to help the plant adjust. This happened to one reader’s Acacia dealbata trees.
Bleeding, resulting from a wound to the plant, is different.
Dew and dewdrops are something entirely different, but are also useful to plants. Plants can maximize dew without being responsible for creating it.
Smart tip about guttation
Guttation can even reach the point where sap drips to the ground. It can leave hard-to-remove stains on almost every surface, indoors and out!
So hose it away outside, and wipe it up indoors.
Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Guttation on grapevine by соннна тетеря under © CC BY 2.0
Leaf blades with guttation by Cynthia Hollenberger under © CC BY-SA 2.0
Guttation on young tomato by Shelly and Roy Johnson under © CC BY 2.0
Guttating orchid by Maja Dumat under © CC BY 2.0
Guttation on rose leaves by Martin LaBar under © CC BY-NC 2.0