Stress Harms Plants Too: Abiotic Plant Stresses

Plants are like people. Their health depends on living conditions, proper nutrition and, just like us, they are harmed by intensive stress — the "enemy of yields". What stress? In this article we will focus on specific stress factors that your plants definitely should not face so you can enjoy a beautiful harvest. Read how to prevent negative influences.

Like humans, every plant has certain genetic predispositions and innate defenses. Modern cultivation, similar to medicine, has effective means to strengthen plants' natural defense mechanisms and practical devices to maintain optimal conditions for their growth and vitality.

Once a plant is repeatedly or long-term exposed to excessive stress, a stress response occurs. The plant's receptors, for example photosensors that react to light intensity, first trigger an internal alarm that activates all available defense mechanisms, helping the plant to keep surviving. This resistance period rarely passes without significant damage; the plant is usually harmed or sometimes even completely destroyed by exhaustion, similar to the flower in the picture.

Unlike us humans, plants are sessile. They cannot run away around the corner or go to a spa. Therefore it is the grower's task to balance suitable conditions so that the plants they care for remain calm and full of life. Below we will go through the most common abiotic stress factors. From the grower's perspective this term can include flooding, nutrient deficiency, too high irradiation, low temperatures and similar. As the saying goes, too much of anything is harmful — and that applies in the plant kingdom too. Stress can be caused by lack as well as excess. We often encounter combinations of several factors at once. For example wilting, primarily caused by lack of water, can also be a reaction to excessive irradiation. A plant's ability to tolerate stress depends mainly on its intensity and duration. Heat stress can destroy a crop in a short time; water shortage can do so over several days.

Physical stress factors

• extremely high or low temperatures
• drought (water deficit), as well as overwatering or flooding
• mechanical damage

One of the most common abiotic stressors for plants is an unsuitable climate. If you grow outdoors, increased care for plants is needed every year, especially during hot summers. Individual species have their temperature optimum, which we can meet perfectly especially when growing indoors. The microclimate inside a grow box or a grow room can be comfortably regulated thanks to fans and ventilators, and if necessary heating. Changes in outdoor temperatures often require adjustments to indoor settings as well. In summer heat your plants will welcome CMH or LED lighting because they emit less heat into the growing environment.

Cold can be as destructive as heat for plants, and outdoors (or in a large outdoor greenhouse) frost can be devastating. Under low temperatures, cellular structures inside plants change, growth slows down and leaves lose color. During frosts tissue damage occurs. Some crops, such as tomatoes or beans, are particularly sensitive to cold.

Always protect roots as well as above-ground parts of the plant from borderline temperatures.

In hydroponics, protect nutrient solution tanks from direct light and maintain a temperature of 18-26 °C. Tank cooling can help with this.

Maintaining optimal air temperature and humidity using humidifiers and digital measuring devices is relatively easy, but many beginners make mistakes when placing the sensor of a combined heat-hygrometer, which should be part of every grower's basic equipment. We recommend placing the probe in the upper third of plant height, i.e. just below the top. Circulation fans are an ideal helper that ensures continuous air flow around the plants. Higher humidity needed for seedlings is best maintained when pre-growing in small greenhouses and propagators.

Dry conditions are associated with reduced air humidity and are generally better tolerated by plants with a shorter life cycle. A dry substrate, however, is clearly bad because it does not support the development of new roots. Nature equipped leaves with microscopic stomata that open and close depending on air humidity. When a plant senses dryness it closes stomata to prevent water loss. The problem for growers is that closed stomata do not combine well with effective photosynthesis. Watch out for dehydration throughout the growing cycle. The best prevention is regular watering.

The mentioned abiotic factors are also well prevented by innovative perforated pots from the brand Hercules and other fabric pots, which help with proper watering and maintain optimal aeration of the root system.

Recommended temperature and humidity ranges for indoor cultivation:

For the vegetative (growth) phase the ideal temperature under lights is 21-28 °C, at night 18-23 °C, and humidity between 50 and 70 percent. For the flowering and fruiting phase a lower humidity of 35-50% is recommended with daytime temperatures of 21-26 °C and nights between 18-23 °C. Seedlings benefit from higher humidity up to 80%.

Chemical stress factors

• Nutrient deficiency of plants and substrate

Proper, or rather rich, plant nutrition is the foundation of a healthy and juicy harvest. Today's grower has so many options that this stress factor can practically be eliminated with appropriate plant care thanks to a wide range of fertilizers and supportive additives for both growth and flowering phases. Just equip yourself with suitable nutrition so the plants and their roots lack nothing. You can also encounter oxygen deficiency, so do not forget adequate aeration of the substrate, which can be achieved, for example, by perlite.

In the case of soil, another pitfall related to chemical processes affecting the plant is salinization. Soil salinity, whether natural or artificial, reduces water uptake.

It is also important to ensure that the plant does not have to face high concentrations of toxic ions and heavy metals such as mercury, aluminum or cadmium. Toxins may also be present in polluted water, so the type of water you use for growing and watering matters. (This topic is so important that we will dedicate a separate article to it soon.) The presence of toxins disrupts nutrient uptake from water or soil and disturbs mineral balance. Heavy metals not only directly threaten the life of the plant, but can completely spoil the final crop!

• Polluted air

Just as toxins can act from the soil, plants and agricultural crops absorb many harmful substances (especially when grown outdoors) from the air, which of course harms them. We are primarily talking about oxygen radicals such as ozone, whose excess around green parts of plants significantly accelerates aging processes. Besides ozone, growers also encounter effects of sulfur dioxide, ammonia and nitrogen oxides.

• Excess light

Excessive amounts of light also contribute to the formation of oxygen radicals. The result is destruction of chlorophyll. Simply put, do not overdo it in a grow tent or greenhouse. Outdoors, use gardening instincts together with information about the planted species to give them the appropriate amount of exposure.

We believe the time you spent reading will help you avoid common practical mistakes that cost both plants and your wallet, and we wish that the plants in your care do as well as possible! If you want to ask us anything, we are here for you every day — call or write to info@higarden.cz, so that growing with us is a pleasure.

• Perlite
• LED lighting
• CMH lighting
• Temperature and humidity meters
• EC / pH meters