Stronger roses in the summer

Marjoland is, with 20 hectares, the largest rose nursery in the Netherlands. It grows five different varieties of the colours red, white and pink. In 2013 the entire roof was coated with ReduFuse.
“We are convinced about the advantages of diffuse light,” says operations director Johan van den Nouweland. “In the summer there is so much light available that the top parts of the plant can’t utilise it all. There are clear advantages to making the lower leaves more productive.” The result was a greater number of roses in the summer without any loss in length.

In addition the autumn growth continued well and production was high. “Therefore creating diffuse light by using the coating suits us very well. But we did find one disadvantage with ReduFuse: We couldn’t use the roof sprinkler system because then the coating turned transparent. We use the roof sprinklers in the summer for cooling and humidification,” he says. 
The solution was to use ReduFuse IR. Because this coating keeps out infrared light, less heat enters the greenhouse which reduces the need for cooling. In addition this coating does not turn transparent if it gets wet. It was applied in May 2014 and removed 10 August.

“The result is less heat and less evaporation, while the PAR-light remains at the same level. That led to a stronger stem and a larger bud in the middle of the summer due to the lower plant temperature,” says Van den Nouweland. He is not quite sure if he finds this necessarily positive. Of course, a strong stem and a larger bud are important quality characteristics, but they harvested fewer roses. “It seems that the plant can only produce a certain number of kilos per week,” he says.

The nursery is always trying to make improvements including in this area. He has his own thoughts about the ideal coating: “If I could choose, I would shade half the amount of infra red. Too much shading substantially reduces transpiration and we steer the plants a lot with this. Some varieties transpired too little this (cold) summer. We are discussing with Mardenkro our approach for next year. We are very satisfied with diffuse light and now we are now trying to fine-tune the blocking out of the heat radiation (infrared).”
The coating also forced a change in their screening and ventilation strategy. “With each development you have to look again at how the plant and the climate respond. That is not so complicated. With diffuse light you can screen later or omit it altogether. Because the temperature rises less quickly under ReduFuse IR, you can ventilate less and thereby retain more CO₂ inside. We will continue to use a diffuse coating, preferably a combination of regular ReduFuse and ReduFuse IR. We are still looking at ways to improve the system; that’s always our approach.”