Abiotic stress is damage caused by the non-living conditions around a plant, such as heat, light, water, salt or a chemical spray. Damage caused by living organisms is called biotic stress. Both kinds can look alike on a leaf, but they need completely different fixes. This guide covers the main types of abiotic stress and what happens inside the plant. It ends with a five-clue check you can run before you spray or feed anything.
The non-living causes are:
- heat or cold
- light that is too strong or too weak
- too little or too much water
- humidity
- salty soil or too much fertilizer
- wind
- nutrient imbalance
- chemical injury
Biotic stress comes from insects, mites, fungi, bacteria and viruses. For a full overview of these, see cannabis pests and diseases.
In a real grow, several abiotic causes usually hit at the same time. A common example is heat plus drought plus strong sun. Inside the plant, the response runs mainly through a stress hormone, through the leaf pores closing and through a build-up of reactive oxygen. Each of these is explained below.
This guide combines several sources of equal weight. Four are extension services, the advisory offices of US agricultural universities that answer farmers’ questions: Penn State Extension (Pennsylvania State University), Virginia Tech (a university in the state of Virginia), Washington State University (WSU) and Cornell Cooperative Extension (Cornell University, New York State). It also draws on three scientific review papers. All sources are listed under References at the end.
The main types of abiotic stress
Penn State Extension defines abiotic disorders as problems caused by non-living factors. These include environmental extremes, nutrient imbalances, physical injury and phytotoxicity, which means plant damage from a chemical you applied. Virginia Tech’s diagnostic guide sorts these disorders into three groups:
- Mechanical: breakage and impact.
- Physical: temperature, light, moisture and oxygen.
- Chemical: chemicals that injure plants, and nutrition disorders.
| Stress | What happens | Typical signs |
|---|---|---|
| Heat | Leaf tissue overheats and dries out | Damage on the most exposed, hottest leaves, often the same across many plants |
| Too much light | A sudden move from weak to strong light destroys chlorophyll, the green pigment that captures light | Yellowing and dead patches on upper leaves, like sunburn |
| Too little light | The plant gets too little energy to grow | Slow growth; flowering reduced, delayed or missing |
| Drought | Not enough water | Older leaves yellow and drop first; wilting; tips and areas between the veins of newer leaves die |
| Waterlogging | Roots run out of oxygen | Wilting and deficiency signs, much like drought |
| Salinity or too much fertilizer | Salts damage roots and cut water uptake | Brown leaf tips and edges; wilting even when the medium is wet |
| Cold | The least hardy tissue is hit first | Exposed foliage dies; root damage in containers |
| Wind or impact | Parts of the plant break | Broken or torn tissue, often on one side of the plant |
| Nutrient imbalance or wrong pH | Deficiency, toxicity or nutrient lockout (nutrients are present but roots cannot take them up) | Leaf yellowing (chlorosis) in patterns on old or new leaves |
For more detail on the last row, see pH and EC and reading nutrient deficiencies from leaves. For salt and fertilizer damage, see nutrient burn.
Some details from the sources change how you read these signs:
- Drought and waterlogging look the same. Virginia Tech explains why. Waterlogged roots stop working, so the plant cannot take up water, even though the medium is wet.
- Cold mainly damages roots in pots. Virginia Tech notes this is mostly a problem in containers, because the root temperature in a pot swings more than in the ground.
- Salt has the same effect as drought. WSU explains that high salt levels in the soil damage roots and reduce water uptake. The plant is then short of water even though water is there.
Two common grower cases also belong in this group:
- Lamp too close. A plant that grows up too close to a lamp can get leaf burn and dry out from the heat. You have to adjust the lamp height for the heat that lamp gives off.
- Clones moved straight into strong sun. Virginia Tech’s rule is that plants need time to acclimate, meaning to adjust step by step to new conditions. That is why clones taken from indoor light straight into strong outdoor sun can scorch. See hardening off seedlings and clones.
What to do: when you find damage, write down everything that changed in the last few days. That includes weather, lamp height, watering, feeding and sprays. Abiotic damage usually follows a change, so this list often points straight at the cause.
Overwatering or underwatering: reading a wilting plant
Wilting can mean the plant has too little water or too much. From above, both look alike.
- Too little water (underwatering): older leaves yellow and drop first, the plant wilts, and the tips and areas between the veins of newer leaves die.
- Too much water (overwatering): the roots run out of oxygen and stop working. The plant then wilts and shows deficiency signs, just as if it were dry. For what roots need, see the root zone.
The leaves cannot tell you which problem you have, but the medium can. Before you do anything, push a finger into the medium and lift the pot.
- Dry, light pot plus wilting: the plant is short of water. Water it thoroughly.
- Wet, heavy pot plus wilting: the roots are short of oxygen. Do not water. Let the medium dry out and improve drainage (see the next sections).
Cornell Cooperative Extension explains why overwatering is so common in humid weather. Plants lose water by transpiration, which is water evaporating out through the leaves and pulling more water up from the roots. With high humidity and low light, plants hardly transpire, so wet soil stays wet. A watering schedule that worked in the dry season can drown roots in the rainy season.
What to do: water by the weight or feel of the pot, not by the calendar. Lift a pot right after watering and again when it is ready for water. Learning these two weights gives you a quick check you can do every day.
What happens inside the plant
This section explains how plants respond to abiotic stress. It shows why growth slows before you can see any damage.
The stress hormone ABA and the leaf pores. Stomata are tiny pores in the leaf surface. A 2026 review of drought stress in cannabis describes them as controlling how much carbon dioxide the leaf takes in and how much water vapour it loses. When water runs short, the plant produces a hormone called abscisic acid (ABA). A review in Frontiers in Plant Science explains what ABA does under drought, salt or cold stress:
- It closes the stomata to save water.
- It switches on genes that help cells adjust their internal water and salt balance (osmotic balance).
The cost: less photosynthesis. Closed stomata save water, but they also block carbon dioxide. The cannabis review notes that this limits how much carbon dioxide gets into the leaf, so photosynthesis drops. Without that energy the plant grows more slowly. This is why growth slows well before any damage is visible.
Reactive oxygen species (ROS). ROS are highly reactive forms of oxygen, such as hydrogen peroxide. Plants produce more of them under both biotic and abiotic stress. A 2022 review describes their two roles:
- They damage proteins, DNA and fats in the cells (oxidative damage).
- They also act as signals that switch on stress-response genes and the plant’s own antioxidant genes.
Recovery. The cannabis review brings good news. Once water is available again, the stomata reopen and photosynthesis recovers quickly. Drought that is not severe or long lasting mainly limits how the plant works for a while. It does not cause permanent damage to the plant’s structure.
The target range. The same review gives typical good conditions for cannabis as about 25–30 °C. Some cultivars handle up to 35 °C. Relative humidity should be about 55–60% in both the vegetative and flowering stages. In tropical lowlands, hot-season afternoons and monsoon humidity can push a greenhouse or balcony grow well outside this range.
Translator’s note: in Thailand and much of Southeast Asia, many grow rooms and greenhouses go well above 30 °C on hot afternoons, and rainy-season humidity often stays high day and night. Power cuts make this worse. When fans and air conditioning stop, a closed room heats up fast. The next day you may see even heat damage across the canopy, and nothing you spray will help it. See grow room climate control and growing outdoors in a tropical climate for ways to bring a room or field closer to the target range.
What to do: put a thermometer-hygrometer that records the day’s highest and lowest readings at canopy height. Read it every day for two weeks, and note any power cuts. You will learn how often and at what time of day your plants leave the 25–30 °C and 55–60% range. Then you will know whether to fix cooling, airflow or humidity first.
How to tell abiotic stress from pests and disease
| Clue | Points to abiotic stress | Points to pests or disease |
|---|---|---|
| Living organisms or their traces | None found | Insects, mites, webbing, insect droppings (frass), fungal spores |
| Which plants are hit | Several species or plants of different ages at once | Mostly one kind of plant |
| Pattern of damage | Even across an area or across the whole plant | Scattered, random, in patches |
| Over time | Does not spread; appears at one moment | Spreads out from a starting point and gets worse |
| Start | Often sudden, after a weather change or a change in care | Often gradual |
Each source adds one clue:
- Penn State: if you see symptoms but no sign of a pest or disease organism, suspect an abiotic disorder. Abiotic disorders also often hit many plant species at the same time.
- Virginia Tech: damage from living organisms usually spreads over time. Non-living causes damage the plant at one point in time, and that damage does not spread.
- WSU: fertilizer burn in particular is usually spread evenly over the plant. Many disease and insect problems are not.
Keep two warnings in mind.
Some pests are too small to see. Penn State reminds growers that many organisms are microscopic and easy to miss. Before you rule out mites, check the undersides of leaves with a hand lens, which is a small, strong magnifying glass.
Stress and pests often arrive together. Virginia Tech notes that some pests, such as borers in trees, mainly attack plants already weakened by water stress or other physical stress. WSU notes that aphids and mites thrive on the soft growth that heavy fertilizing produces. Fixing the stress is not always the end of the problem. After a stress episode, check leaf undersides with the lens every few days. This lets you catch an infestation while it is still small.
Translator’s note: if the check points to a pest or disease, use only pesticides registered with Thailand’s Department of Agriculture (กรมวิชาการเกษตร), exactly as the label says. See what you may legally spray under Thai GACP. If you cannot tell the cause yourself, a plant clinic may be able to examine a sample. One example is the Plant Disease Clinic of the Department of Plant Pathology, Faculty of Agriculture, Kasetsart University, Bangkok. Contact the clinic first to ask whether it accepts samples from growers and how to send one.
What to do: before any spray, go through the five clues in the table and write down which column each answer falls in. If most answers point to abiotic stress, fix the conditions and do not spray. That saves money and spares the plant a second stress.
Managing abiotic stress in a hot, humid climate
- Heat and light. Keep lamps at a safe distance, add airflow, and use shade cloth outdoors. Move plants into stronger light step by step. This prevents leaf scorch from heat and from a sudden jump in light. For light strength, see light spectrum and DLI.
- Water. Water by the weight or feel of the pot, not by the calendar. In humid, low-light weather the plant uses little water, and wet soil stays wet. In Southeast Asia this is the rainy-season trap.
- Drainage. In the rainy season, raise pots off the ground and use a free-draining medium. Excess water then runs out quickly, so roots keep their oxygen and the plant avoids waterlogging.
- Feeding. WSU advises never to fertilize plants stressed by heat or drought. Water first and feed only after the plant has recovered. Fertilizer adds salt, and salt cuts water uptake even more.
- Humidity and calcium. Cornell explains that calcium travels to new leaves in the water stream that transpiration pulls up. In still, humid air that stream almost stops. New growth can then show calcium problems even when the medium has enough calcium. Improve air movement before you add more calcium, so you fix the cause and do not raise salt levels for nothing.
Translator’s note: during the Thai rainy season, check each of these points again. Look at drainage under the pots, airflow in the room or greenhouse, and the gap between waterings. A rhythm that suited the hot dry months is often wrong once the rains start.
Common mistakes
- Spraying a plant whose problem is heat, light or overwatering. The spray cannot fix any of these and can add chemical injury. Run the five-clue check first.
- Feeding a wilting plant. This adds salt stress on top of water stress. Water first, then feed after recovery.
- Assuming wilting always means dry. Waterlogged roots wilt too. Check the medium with your finger and the pot weight first.
- Moving indoor plants straight into full tropical sun. Increase sun exposure step by step over several days so the leaves can adjust.
- Changing several things at once. Then you never learn what the cause was. Change one thing, wait to see the result, and record it.
Your short check before you treat
- Note what changed in the last few days: weather, lamp, watering, feeding, sprays, power cuts.
- Check the medium: dry and light, or wet and heavy.
- Look under leaves with a hand lens for insects, mites, webbing or droppings.
- Look at the pattern: even and sudden, or patchy and spreading.
- Fix one condition, then record what happens over the next days.
If you are unsure what you are looking at, post clear photos in this topic. Include temperature, humidity, watering and feeding details, and say what changed recently. You can also ask in the Plant Infirmary section.
References
- Penn State Extension (Pennsylvania State University, USA): Mazzone, T. R. and Mazzone, J. D., “Solving the Case of Crop Disorders: The Role of Patterns in Diagnosis” (updated 2024). Abiotic disorders, symptoms without pest signs, many species affected at once, microscopic organisms.
- Virginia Cooperative Extension (Virginia Tech, USA): Virginia Cooperative Extension Gardener Handbook, Chapter 6, “Diagnosing Plant Damage” (mechanical, physical, chemical groups; drought vs waterlogging; cold damage in containers; acclimation; spread of biotic vs abiotic damage). Also Niemiera, A. X., “Diagnosing Plant Problems”, publication 426-714.
- Washington State University (WSU) Extension, HortSense fact sheet “Common Cultural: Fertilizer burn”: salt damage to roots, even distribution of fertilizer burn, not fertilizing heat- or drought-stressed plants, aphids and mites on soft growth.
- Cornell Cooperative Extension, Cornell Vegetable Program (Cornell University, New York State, USA): Grundberg, E., “Environmental Causes of Tip Burn on Transplants” (2018). Transpiration under high humidity and low light, and calcium movement to new leaves.
- Delpasand Khabbazi, S., Park, S.-H., Ryu, B.-R., Da Cunha Leme Filho, J. F., Yılmaz, G., Delpasand Khabbazi, A., Singh, D. and Teotia, S. (2026). “Drought stress in Cannabis sativa L.: current knowledge, research gaps, and future perspectives – a review”. Frontiers in Plant Science 17. doi:10.3389/fpls.2026.1890092. Stomata, reduced photosynthesis, quick recovery, optimal 25–30 °C and 55–60% relative humidity.
- Sah, S. K., Reddy, K. R. and Li, J. (2016). “Abscisic Acid and Abiotic Stress Tolerance in Crop Plants”. Frontiers in Plant Science 7:571. doi:10.3389/fpls.2016.00571.
- Mansoor, S., Ali Wani, O., Lone, J. K., Manhas, S., Kour, N., Alam, P., Ahmad, A. and Ahmad, P. (2022). “Reactive Oxygen Species in Plants: From Source to Sink”. Antioxidants 11(2):225.