Proper water management is crucial for optimal plant health and production in greenhouses. It ensures plants receive the right amount of water at the right time, maximizing growth and yield while minimizing waste and risks. Alessandro Montanarella, consultant at Saint-Gobain Cultilene, highlights the importance of water uptake and explains how to balance water availability effectively. 

The importance of water uptake in greenhouses
As we all know, water plays a key role in plant processes. Not only in growing, but also in processes like evaporation, cooling, and biomass development. Therefore, it is important to give plants the right amount of water during the day. Giving plants too little water can halt growth and cause stress, while overwatering can lead to oxygen deficiency, diseases and inefficient nutrient use. 

One of the well-known problems of over-irrigating tomatoes is fruit cracking, due to rapid osmosis. This occurs when the plant is not evaporating enough yet. Applying too much water to the plant will cause a rapid change in EC, forcing the plant to take up water. Besides cracking of the fruit, this can also lead to discoloration. 

So the question is, what is the optimal amount of water for a plant? The answer heavily depends on the circumstances. Factors like substrate volume, weather conditions and irrigation strategy need to be taken into account when determining the optimal amount of water each day. 

Calculate the required water volume
How do you determine the water required for your crop? A useful rule of thumb is to align the substrate volume per square meter with the daily evapotranspiration rate of your crop. For instance, if a crop requires 7 litres of water per square meter daily, use a similar substrate volume per square meter. This balance ensures that the available water in the substrate is sufficient to meet the crop’s needs, without over-saturating the material. 

Stonewool substrates, for example, can retain about 60-65% water content. As the substrate is not meant to hold 100% water, you have to account for the air and water balance within the substrate to promote healthy root development and avoid oxygen deprivation. This balance directly influences the frequency and amount of water per irrigation.

Seasonal considerations 
Water requirements change throughout the year due to seasonal variations. In spring and summer, warmer and high light conditions increase transpiration rates. Plants need more frequent and precise irrigation to meet these demands. Conversely, during autumn and winter, cooler and low light condition reduce plant activity and water uptake, making it important to avoid overwatering. 

In addition, on rainy or cold days, when plant activity is particularly low, it is smart to regulate greenhouse humidity by using screens, heating and ventilation systems. This helps to prevent stagnant conditions and supports healthy growth of the plants.

Balancing water availability 
Providing sufficient water is not only crucial for plant health, but also helps to prevent the waste of valuable resources. Climate change plays a big role here, as it has led to unpredictable and more extreme weather conditions like sudden heavy rains or prolonged droughts. These shifts can disrupt water availability, especially in drier regions like Southern Europe or North Africa.

Tips for effective water management
To summarize, the best way to ensure adequate water uptake and availability by the plants in your greenhouse, is to closely monitor the irrigation and circumstances. Below are the best tips to do this: 

• Measure and monitor regularly: use sensors and scales to track substrate moisture and water uptake.
• Adapt to environmental conditions: adjust irrigation frequency and volume based on expected light, temperature and humidity levels.
• Avoid overwatering: prevent diseases and fruit cracking by irrigating only when plants are ready to absorb water.
• Optimize substrate use: match substrate volume with plant water needs for consistent growth and minimal waste.

Maximize growth with precise water management
By aligning irrigation strategies with plant needs, you can optimize growth, enhance yield, and reduce waste of valuable resources. 

The information provided by Saint-Gobain Cultilene has been compiled with great care and is intended solely as a guideline for the user. Saint-Gobain Cultilene therefore cannot guarantee any errors and no rights may be derived from the information or advice provided. The user himself is responsible for checking the accuracy and suitability of the information and advice for application. No commercial use may be made of the information and advice provided by Saint-Gobain Cultilene, in whole or in part, without the written consent of Saint-Gobain Cultilene.