Heat stress in plants: symptoms and treatment

Heat can harm plants

Even the hardiest plant can have a hard time during an especially hot summer or a heat wave. But how does it react to a rise in temperatures for which it was not prepared? Thermal stress is a problem that, as fans of gardening and / or agriculture, we must know, since no crop is exempt from suffering it. Believe me, none, although it is true that there are species more delicate than others.

As always it will be better to be safe than sorry, in addition to knowing the symptoms of heat stress in plants, we are going to take some measures to avoid, as far as possible, that our beloved crops have a hard time when the time comes.

How to know if the plant is hot?

Feeling hot is not only done by animals, including us humans. It is often thought that it is, since when we have heat stress we show it, for example, by avoiding going outside during the central hours of the day, drinking a lot of water, or getting into a pool to counteract that feeling.

But plants cannot move. If the seed germinates in the ground, it is normal for it to remain where it took root throughout its life. Only those that we grow in pots have the option of changing places if we take them and move them. For this reason, heat symptoms can be difficult to recognize in plants.

Now, the most common are:

  • Folded or rolled sheets, or on the contrary curved upwards
  • Leaves with brown or dry spots
  • Sad general appearance, with drooping green stems
  • The ground can be dry, and feel very hot if you are outdoors

How to eliminate heat stress in plants?

Eliminating heat stress in plants involves doing several things, which are:


If we have plants that are having a bad time due to heat, it will be necessary first of all to make sure that the soil is moist but also fresh. One of the most serious consequences of heat is dehydration, so it is necessary to check the humidity of the soil to see if we have to water or not.

But also use water that is not excessively hot. Ideally, it should be around 23ºC, especially if it is tropical plants, but it can be between 18 and 30ºC. If it exceeds 30ºC, the water will have less oxygen, so its development will be much slower, and in fact, its roots could suffer burns.

Flower pot

Another topic that we are going to talk to you about is about pots, and that is those made of plastic absorb much more heat than those made of clay. Consequently, a kind of greenhouse effect occurs inside it, overheating the roots and causing damage. For this reason, whenever possible it is preferable to plant them in clay pots, especially if you live in an area where the degree of insolation is high.

In the event that it is unfeasible, either because you cannot get them or because you have many plants or you plan to have them, you have to place them near walls or walls that do not retain much heat. For example, you should not put them next to windows, metal or plastic doors, but rather next to a wall or wall made of concrete blocks, or better yet, next to other plants.

Sun protection

It is the most urgent, but sometimes it is not the easiest to solve. If the plants are in pots and it is seen that they are having a hard time due to the high temperatures, we can take them to a sheltered place, in semi-shade or shade; but What do we do if they are planted in the ground?

Then, the most effective way is to drive 2-4 stakes or rods into the ground and put shading mesh on toplike an umbrella. If we see that the sun affects a lot on one side of the plant that has been left unprotected, we can choose to wrap it all with the mesh.

Shading mesh types

Shading meshes can be white, brown, green or black, and all of them have a degree of concealment that ranges from 40% to 90%. What does this mean? Well what if for example we buy a 70% mesh, the plants will receive only 30% light.

It must be taken into account, because a cactus for example, which grows in full sun, does not need the same amount of light as a Japanese maple which lives in shade. If we wanted to protect the first we would use a 40% mesh, while to protect the maple it would be better to opt for one of at least 70%.

How to prevent plants from heat stress?

Spraying the plants with water in the afternoon refreshes them

Spraying plants with water in the afternoon refreshes them

As we were anticipating at the beginning, there is nothing to prevent. To do this, we have to:

  • Control irrigation a lotespecially during a heat wave. The earth dries faster, and that can take its toll on the most water-demanding plants, such as Sarracenia, tomato plants, peppers, and many others such as Archontophoenix palms or flowers such as geraniums.
  • Avoid waterlogging. No matter how much water they need, not all plants need to have watery roots (only aquatic ones). If the substrate or soil takes hours or days to absorb the water, we will have to take steps to improve drainage.
  • Treat them with natural biostimulants following the directions for use. For example, a foliar biostimulant such as this it will help them cope better with the heat.
  • Refresh them in the late afternoon. When the sun is low, it is a good time to grab the hose and spray it with water. This is great for them after a day in which the temperatures have been especially high. In addition, it will help you to spend better tropical nights (they are those in which the thermometer does not drop below 20ºC).
  • And last but not least: we advise growing native plantsor climates similar to ours. Although more and more lasting heat waves are going to occur, if we opt for these species we will have a better chance of having a healthy garden or balcony, which will not suffer much from the heat.

We hope these tips have helped you.

Heat stress in plants: symptoms and treatment

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