Heat stress Heat stress is one of the most common and dangerous threats to plants, whether ornamental, indoor, outdoor, agricultural, or wild. Even the most resilient plants can be affected during episodes of high temperatures, whether in intense summers or in heat waves that are becoming more frequent due to climate change. But how can heat stress be detected in plants, and what are the best strategies to prevent and treat it?
This article offers a comprehensive, clear and practical guide to Identify the symptoms of excess heat in plants, understand the physiological mechanisms involved, identify the types of damage they can suffer, and apply effective treatments, both preventative and curative. All of this is geared toward helping both gardening enthusiasts and farmers maximize the health of their crops and gardens, minimizing damage and increasing plant resilience.
Discover everything you need to successfully address the challenge of heat stress and achieve healthier, more productive, and resilient plants, integrating the most up-to-date knowledge and best practices recommended by leading experts and sources in agriculture and gardening.
What is heat stress in plants and how does the weather cause it?
El heat stress or heat stress In plants, it is a pathophysiological process that occurs when the environment exceeds the optimal temperature range that a plant species can withstand without suffering severe alterations. For most crops and plants, the ideal development range is between 20 and 30°C. When temperatures, whether air or soil, exceed these limits for an extended period, the plants' vital functions are affected.
The phenomenon is aggravated in situations of heat waves, on consecutive days with high temperatures and on soils without sufficient moisture. The effect is cumulative, depending on the intensity of the heat, its duration, and the speed with which the temperature increases.
Not all species tolerate heat equally. Some, such as succulent plants, are adapted to aridity due to their ability to store water, while others, especially those from cold or humid climates, are much more vulnerable. However, no plant is completely immune to the consequences of overheating and dehydration.
Why do plants suffer so much in extreme heat?
Plants, unlike animals, remain fixed in the place where they germinated and took root. This means they cannot move to seek better conditions or seek shelter in the shade. If climatic conditions exceed their limits, they depend exclusively on their physiological defense mechanisms, the help we can provide, and their genetic adaptation to survive.
El extreme heat It triggers a series of cascading reactions in plants that affect:
- Photosynthesis: worsens by stomatal closure, enzyme denaturation and damage to pigments.
- Perspiration: increases excessively, causing rapid water loss.
- Cellular respiration: accelerates, increasing the consumption of energy reserves and decreasing metabolic efficiency.
- Cellular integrity: High temperatures can disrupt membranes and denature vital proteins.
- Production reactive oxygen species (ROS): Heat increases oxidative stress, damaging lipids, DNA, proteins and cellular structures.
The result is a general weakening, wilting, loss of turgor, burns, necrosis, flower and fruit drop, and even death if the stress is prolonged too long.
Main causes of heat stress in plants
- High ambient temperatures due to heat waves, dry summers, prolonged exposure to direct sunlight or overheated soils.
- Water deficit due to lack of irrigation, drought, poor water management or soils that are poor in moisture retention.
- Poor choice of planting location, where there is no shade or it is exposed to walls or surfaces that radiate heat.
- Unsuitable pots or containers made of plastic or metal, which overheat and damage the roots.
- Poor quality soil or substrate, without organic matter or with poor drainage, which does not facilitate water absorption and root aeration.
- Chemical fertilizations or treatments poorly applied during hot weather, they can burn the roots or create osmotic imbalances.
- Presence of pests and diseases which aggravate the general weakening of the plant.
The combination of several of these factors can have devastating consequences for any crop or garden.
How do you know if a plant is suffering from heat stress?
Recognize in time the symptoms of heat stress It is essential to act quickly to avoid irreversible damage. Signs can vary depending on the species, stage of development, and severity of the heat, but the most common include:
- Folded, rolled or curled leaves: Defense mechanism to reduce the surface area exposed to the sun and water loss.
- Leaves with brown, yellow, or dry spots: Indicates dehydration, necrosis or sunburn, very visible on the margins and tips.
- Death of tissues between the veins or scalding: Dry, brittle or discolored areas may appear, especially on fruits and leaves exposed to direct sunlight.
- Dry or burnt leaf edges: Typical symptom of species such as pumpkins, cucumbers, tomatoes and many ornamental plants.
- Wilting or general listless appearance: The plant loses turgor, the stems droop and it does not recover even after watering during the day.
- Premature fall of flowers, fruits and leaves: The body prioritizes the survival of vital organs and sacrifices less essential structures.
- Growth arrest: New shoots that do not develop or remain stunted.
- Dark, watery or sunken spots on fruits: It is usually a result of sunburn or damage to the flower tips of tomatoes and other horticultural crops.
- Easy touch sheet detachment: They become brittle or even disintegrate due to severe cellular damage.
- Unusual pale, yellowish, or reddish coloration: By destruction of pigments (chlorophyll or anthocyanins) or cell death.
- Presence of pest- or disease-like symptoms: Heat stress weakens the plant, making it more susceptible to infections and insect attacks, or confusing diagnoses.
- Sensitivity to touch: Leaves or fruits may easily come off or have an unusually soft texture.
It's important to assess the climatic context and irrigation history to distinguish these symptoms from nutritional or pest problems. Furthermore, if the plant's turgor improves at night, it's usually due to reversible water or heat stress, while if it doesn't recover, the damage may be permanent.
Types of damage caused by heat stress in plants
- Severe dehydration: Causes a decrease in water pressure in cells and tissues, leading to permanent wilting.
- Reduction or blockage of photosynthesis: By closing stomata and denaturing enzymes, limiting the production of sugars and energy, leading to weakening and delayed growth.
- Cellular oxidation damageExcess heat generates an increase in ROS (reactive oxygen species) that destroy membranes, proteins and DNA.
- Alterations in the absorption and transport of nutrients: Deficiencies in calcium, potassium and magnesium, essential for water balance and heat resistance, are aggravated.
- Failure in the formation and quality of flowers, fruits and seeds: Premature fall, low setting and the appearance of apical necrosis or rot in fruits occur.
- Greater vulnerability to pests and diseasesStress weakens natural defenses and facilitates the emergence of pathogens.
- In extreme circumstances, death of the plant: If the combination of heat and drought persists without intervention.
How to differentiate heat damage from other causes?
It is not always easy to distinguish heat stress of problems related to diseases, nutritional deficiencies or pests. However, the location of the damage (areas most exposed to the sun and extreme temperatures), the speed with which symptoms appear during a heat wave, and the presence of daytime wilt that improves in the evening are clear indicators.
The combination of symptoms such as dry or burnt leaves at the margins, flower and fruit drop, general decline and delayed growth during periods of intense heat is usually characteristic of heat stress.
How to eliminate heat stress in plants? Curative treatments
Once a plant has begun to show symptoms of heat stress, it's crucial to act quickly to stop the damage and ensure the plant is in the best possible condition to recover. Recommended treatments include:
1. Optimal irrigation and humidity control
It is essential to ensure that the substrate or soil is always humid but coolLack of water is one of the main causes of thermal damage. It is recommended to:
- Water in the early morning or evening to avoid loss through evaporation and help the plant recover its turgor.
- Never water with excessively hot waterIdeally, water should be at room temperature, between 18°C and 30°C. Warmer water can damage roots and limit oxygen content.
- Avoid waterloggingExcess water causes a lack of oxygen and promotes fungal diseases.
2. Improve the structure and location of the pots
The plastic pots They tend to absorb and retain much more heat than clay or ceramic ones, generating a Greenhouse harmful to the roots. When possible, it's preferable to plant in clay pots. If you only have plastic pots, place them in locations protected from direct sunlight or next to walls that don't accumulate heat, and never on metal or stone surfaces that get hot.
3. Protect from direct sunlight
Moving potted plants into the shade during the middle of the day is very effective. If they're planted in the ground or can't be moved, use:
- shade nets (green, brown, black or white) with shading percentages of 40% to 90%, depending on the species.
- Install the shade netting on stakes or a support structure, making sure to fully protect the top and sides exposed to the sun.
- For full-sun species (cacti, succulents), choose light shade (40%). For delicate or shade-loving plants (maples, ferns), opt for higher percentages (70% or more).
4. Application of mulching or padding
El padded Mulching with organic materials (straw, pine bark, dried leaves, compost) helps retain moisture, reduces evaporation, and keeps the soil temperature lower. A 5 to 10 cm layer is very effective in protecting roots and preventing sudden temperature fluctuations.
5. Use of biostimulants and specific phytosanitary products
- Foliar biostimulants Enriched with amino acids (proline, glycine, arginine), antioxidant vitamins (C and E), polysaccharides and polyamines, which reinforce the plant's resistance to stress and promote the recovery of damaged tissues.
- calcium supplements and potassium to prevent apical necrosis in fruits such as tomatoes and peppers, and strengthen cell walls.
- Always apply these products following the manufacturer's instructions and avoiding periods of maximum sunlight.
6. Pruning and removing damaged parts
Withdraw leaves, flowers and fruits Severely damaged leaves should be trimmed to promote air circulation and allow the plant to dedicate its resources to the healthiest areas. Do not remove partially affected leaves if they are still performing photosynthetic functions and providing shade to the rest of the plant.
7. Avoid fertilization during heat waves
During episodes of extreme heat, It is not advisable to pay Since the plant is unable to assimilate nutrients or grow properly, this can cause burns or imbalances. Wait for temperatures to normalize.
8. Pest monitoring and control
Weakened plants are more susceptible to red spider, mites and fungi. Periodically review and apply safe pesticides if necessary, prioritizing natural products compatible with insect aids and pollination.
9. Use of natural reflective products
In commercial or fruit crops, products such as kaolin, which forms a protective white film on leaves and fruits, reflecting radiation and reducing damage from burns, evaporation and stress.
How long does it take for a plant to recover from heat stroke?
Recovery time depends on the severity of the damage, the type of damage, and the speed with which corrective measures are implemented. It can range from few days For light damage and resistant plants, up to Several months If there has been loss of leaf mass, roots, or deep tissue damage. In extreme cases, if the plant shows no signs of recovery after weeks of care, the damage may be irreversible.
Guidelines to help plants recover faster from heat stress
- Provides immediate shade and sufficient moisture.
- Avoid transplants, drastic pruning, or sudden changes in the environment during recovery.
- Do not fertilize until the plant shows clear signs of recovery.
- Remove flowers or developing fruit if the plant is too weak so it can concentrate on surviving.
- Increase pest and disease surveillance throughout the stress and recovery period.
What practices help PREVENT heat stress in plants?
La prevention It's more effective than curative treatment. Before extreme heat hits, apply the following strategies:
- Comprehensive irrigation control: Schedule watering based on plant type and weather. During heat waves, increase the frequency but reduce the amount to avoid waterlogging. Use drip irrigation, mulching, and moisture sensors whenever possible.
- Shade strategically: Install shade nets, awnings, green screens or use companion plants that provide natural shade.
- Refreshes plants at dusk: Gently spraying water on the leaves can help reduce the temperature, but always do so outside of daylight hours to avoid burning.
- Avoid waterloggingOnly aquatic plants tolerate waterlogged roots. If the substrate doesn't drain well, improve its permeability.
- Corrects the substrate and improves soil fertility: Add organic matter, compost and materials that retain water, but ensure good drainage.
- Rotation and choice of species: Preferably cultivates native plants or species adapted to the local climate. They are more resistant to extreme conditions. These include heat-resistant plants such as bougainvillea, aloe vera, bay leaves, ivy, and certain grasses.
- Fertilize only at the appropriate times: Boost nutrition in spring and fall, not during peak heat.
- Apply preventive biostimulants: They strengthen general resistance and the ability to respond to stress.
- Eliminate weeds: They compete with cultivated plants for water and nutrients.
- Control the environment: If you grow in a greenhouse, use ventilation, misting and interior shading.
The key to keeping a garden or crop productive during heat waves lies in constant vigilance, flexibility, and the adoption of preventive and corrective practices based on scientific knowledge and experience.
Paying attention to early symptoms, optimizing irrigation, providing shade, and protecting the soil with mulch are key factors in helping our plants cope with the heat. Choosing native species, using biostimulants, and technological support will be increasingly important in the gardening and agriculture of the future.