Johan and Piet Reedijk run three nurseries at two locations in the Netherlands; in Strijen, Hoeksche Waard (2 x 3ha) and Westdorpe in Terneuzen (8 ha). They grow sweet and chilli peppers in all shapes and colours: large and small, sweet and hot. An unusual feature is that their nursery in Westdorpe, Zeeuws-Vlaanderen, does not have a natural gas connection. All heat comes from industry, which otherwise would burden the environment. “Just for insurance we do maintain a back-up in the form of an oil boiler. But that has run for barely three hours,” says Johan Reedijk.

The sweet pepper nurseries run by the Reedijk brothers, in Strijen and Westdorpe, the Netherlands, were some of the first to use ReduHeat. A difference of opinion prevails among pepper growers as to whether shading with a coating is necessary. It is certainly true that the fruits can suffer from heat stress. “At such moments of stress there is a risk of problems with quality, such as blossom end rot and “burnt shoulders”. We are convinced of the benefit of ReduHeat to shade out the heat,” he says. “That has partly to do with the position of our greenhouse. The ridge is orientated in an east-west direction.” That is positive for light transmission in the winter but it requires extra attention in the summer to prevent too much radiation entering the greenhouse. This can be achieved by using an energy screen or a heat reflecting coating. Reedijk prefers to use a coating because then he can better steer the greenhouse climate. “Quality is a high priority for us. With ReduHeat we can keep the technical aspects of production well under control. In a moderate climate the size of the fruits is better. If there is too much radiation the plants make more fruits and these are automatically smaller.”

Both in Zeeuws-Vlaanderen and on one of the nurseries in Hoeksche Waard the coating is applied with a helicopter. The reason for this is the speed of application. The vents have to be closed during coating and so Reedijk wants this to happen as quickly as possible. “In addition coating with a helicopter produces a somewhat larger droplet. We’ve noticed that for us this produces a better effect. We have experimented a lot to find the right thickness of coating and now we’ve found the right dosing for all the nurseries,” he says.

ReduFuse IR
Last year they tried ReduFuse IR, the diffuse coating that also reflects heat. The grower was less positive about this. “Because diffuse light penetrates deeper into the crop we had more settings at the bottom. Peppers always have some after flowering at the bottom of the crop but this increased slightly. That is tricky: You see the fruits aren’t hanging properly but to going through the crop just to pick these is difficult to do profitably. Therefore we simply went back to using ReduHeat. We are satisfied with this.”

Adjust cultivation
Certainly in the beginning of spring you have to pay attention, he admits. “You benefit less from the first rays of sunlight that heat the greenhouse. Therefore early in the morning you have to provide some extra heating, about 1.5°C above the standard setting. On the other hand you can keep the vents closed for longer and therefore keep more CO2 inside. We haven’t calculated exactly if these outweigh each other but we have a good feeling about it.”

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