VLAARDINGEN, The Netherlands: During summer the control of greenhouse climates requires a different strategy to avoid plant stress for example, caused by an increase in temperature and radiation. Hoogendoorn, a leading supplier of climate and automation solutions in horticulture, provides growers useful tips.
Tip 1: optimize your screening strategy
During the summer period a high level of radiation has a large effect on the crops. When plants start to feel stressed, it is necessary to reduce the energy supply by closing the climate screen.
There are three ways to do this:
- The easiest way is to close the screen, based on a set level of radiation. However, usually this measure is often taken very ‘prudently’ which unnecessary limits growth.
- The second method is to adjust the set point to the level of greenhouse humidity. In most cases this is done based on Relative Humidity (RH). This means that the screen closes when the RH is too low combined with a certain level of radiation. In the case that the RH level is correct, the screen remains open.
- Plant stress is measurable with a plant temperature meter. In the case that the plant temperature exceeds the greenhouse temperature, it is a sign that plants can’t cool down, because plants cool down due to evaporation, this means the risk of water stress increases.
With this knowledge you can increase the light level when the greenhouse climate is correct. At days that plants struggle more to retain the photosynthetic process, you reduce the light level. On average this increases crop growth.
Tip 2: Optimize greenhouse temperature control
The temperature control has a large influence on the speed of growth. High temperatures can cause an unbalanced plant and even water stress. During summer, you as a grower, face a dilemma: do you need to reduce temperature by ventilation, or do you need to close vents to maintain the right level of humidity and reduce CO2 loss?
Research shows that water stress in the late afternoon is caused by a low level of humidity. This means that a high temperature has less influence. On the contrary, a high temperature combined with a high level of radiation increases the photosynthesis. This benefit only applies when the stomata of the plants are opened for uptake of CO2.
To create a win-win situation for the plant, we advise you to increase the set point of the ventilation. This prevents a low level of humidity: the temperature increase is much less as expected.
With over 49 years of experience in hortcultural automation, Hoogendoorn has much in-house knowledge. Via (customized) training knowledge is shared about safe, efficient, and environmentally friendly production with advisors, students, customers and partners. Training sessions are provided online or in-company, either on an individual basis or in groups.