Dynamic cultivation

Plants often spend extended periods in a fixed spot within the greenhouse. Since they cannot uproot themselves and move to better conditions, your aim as a grower is to continually provide the best possible climate. If you fail to do so, your plants will signal their distress by changing their growth direction, slowing growth, bending, bolting or discolouring. To prevent this, we have always aimed to stabilise daytime growing conditions. In the past, we created these optimal conditions with the tools available; now it seems we are moving away from this approach. But are we really? Perhaps we have always been a dynamic grower. We just didn’t realise it, and we didn’t act like it.

Heat accumulation

We now have additional (and better) sensors, allowing us to measure and understand greenhouse conditions more accurately, particularly those around the plant. Most of you will know that the type of light source significantly affects plant and substrate temperatures. Radiant heat raises the temperature of plants and substrate without affecting the ambient temperature. Our monitoring reveals fluctuations in plant and substrate temperatures throughout the day. For example, plant temperatures rise quickly during sunlight exposure and drop again when shielded — regardless of the climate sensor’s reading.

Our goal is to keep the measured ambient temperature within set parameters by using heating, ventilation, whitewashing, screening, and/or humidification systems. But with the advent of LED lighting, it has become more difficult to detect whether plant or substrate temperatures are rising or falling — or to detect changes at all. This results in lower heat accumulation in the crop, slowing growth. Slightly raising the ambient temperature could remedy this by allowing the plant and its surroundings to heat up more.

However, once the climate sensor returns to the desired level, the difference between plant, substrate and air temperatures disappears; a difference that is created with radiant heat, which promotes better evaporation. As we know, evaporation is crucial to a range of physiological and climatic processes. But is it as pivotal as we believe? Intensifying the difference between ambient and plant temperature to promote evaporation or drying is challenging. That’s why we are monitoring how available options — dehumidification, air circulation or altering humidification settings — impact our plants.

Dynamic temperature

It’s interesting to observe the effects of applying dynamic temperature changes throughout the day, allowing the temperature to rise during daylight hours (exceeding the set parameter) and drop as evening and night approach (falling below the parameter). Over a 24-hour period, the plant’s temperature remains within the parameters, while our net energy consumption is significantly reduced. Considering the plant and substrate temperatures alone, we are essentially working with a process that used to occur naturally to some extent.

Interestingly, various studies have demonstrated that plants are more resilient than previously thought and can even benefit from this strategy. A dynamic approach to ambient temperature does not provoke a negative response in the plant. In fact, the plant or substrate acts somewhat like a ‘battery’, allowing for lower minimum and maximum temperature.

In terms of dynamic lighting, we can reduce costs by timing when lamps are switched on or off based on energy prices. This marks a shift in our approach, which aimed to keep cultivation as stable as possible throughout the day to achieve optimal plant growth. However, with energy prices rising sharply, it’s worth investigating the fluctuations that plants can tolerate.

Considerable effort has already been made to reduce costs, including replacing SON-T lamps with LED lamps. The next step is to integrate these lamps into a dynamic cultivation scheme. Our crops seem to offer opportunities in this regard, as long as we don’t overdo it. There is a limit to how many times assimilative lamps can be switched on and off. But even these limits can be approached dynamically, based on factors such as energy costs and the degree of growth delay or discoloration we are willing to accept, and, perhaps most importantly, whether any shortfall could be compensated for in the following days.

These are all valid questions. While they do not have straightforward answers, they are opening new avenues of research that we are actively exploring.

What does the future hold?

We are seeing a rise in the number of LED systems offering seamless dimming, including those capable of smoothly dimming three or four colours. While this is helpful, it also raises several new questions. Could you intensify the dimming of certain wavelengths more than others at specific times? Could you disable some wavelengths entirely for brief periods? Might you save money by using a different colour spectrum? The short answer is ‘yes, you could’ — but, of course, the reality is more complex.

Our tests have shown that different varieties respond differently, necessitating further research. One challenge is the virtually unlimited number of possible combinations. Nevertheless, there are occasions when it’s possible to reduce costs by increasing the proportions of red light or lowering the amounts of far-red, blue, green (or white).

Replacing our SON-T system with an LED system was a key moment that made us realise the need to become dynamic growers. What once happened more or less automatically now requires skilful management. At the same time, dynamic cultivation allows us to increasingly embed variety-specific growth plans into our practices. These plans reflect the distinct phases of cultivation, optimise resource use and bring us closer to our desired outcomes. So, while the transition to dynamic growing will not be easy, it presents an opportunity to refine cultivation practices and make them fit for the future.