The new diffuse screen from Svensson provides even better light distribution than the previous version. But growers are also still very keen on the first generation of these climate screens. “I would choose this screen again straight away in any new build,” says chrysanthemum grower Wilco Hofman from Bleiswijk in the Netherlands.
The Harmony climate screen slides out slowly below the glass. The young plants underneath are enveloped in light shade. There is a marked difference in the places in the greenhouse that are not screened. The chrysanthemums are still in full sunlight there. “We often use this open structured climate screen, particularly in the bays housing the young plants,” says chrysanthemum grower Wilco Hofman of De Landscheiding in Bleiswijk. “Young plants are delicate. Diffuse light is therefore just what we want in those bays.”
And yet it wasn’t so much for light distribution that he bought the screen back in 2009, but rather to improve the climate in the greenhouse. “It’s an interplay between various factors. Our Santinis almost never get enough light. You don’t actually need to use a screen for plant growth; I mainly do it for cooling and to keep the humidity in the greenhouse stable. If it gets too hot, the plant’s stomata close and the plant doesn’t cool itself. Closing the screen allows the plant to cool down.”
This also has a positive impact on the young rooted chrysanthemum cuttings. The climate screen prevents the roots from drying out unevenly. “I also have an older greenhouse in ‘s-Gravenzande. We use whitewash there. The direct radiation from the open windows dries out the pots more quickly in some places than in others. That means we have to water flexibly there, which makes the crop less reliable.”
Hofman came across the Harmony screen quite by chance. He used to use a blackout screen in his greenhouse and whitewash on the glass. When he was building his new greenhouse in 2009, he temporarily transferred production to a rented greenhouse. This was equipped with a blackout screen with silver-coloured shading above it, which could be closed separately. “It struck me how pleasant it was to work under. The plants are not in full sun, but nor are you yourself. I took the idea back with me to my own greenhouse, and after taking advice we decided to have a new climate screen installed while we were building the new greenhouse.”
He has had a 45% screen ever since. The grower decided to install this open structure screen and the blackout screen together on the same wire frame. “This does mean that we can’t close the screens at the same time, but we never need to do that anyway. Installing them in this way keeps the costs down.”
Less delayed growth
Hofman was the first chrysanthemum grower to have this climate screen installed. “It is certainly not common in chrysanthemum growing,” says Ton Habraken of Svensson, the screen manufacturer. “Santini and disbud chrysanthemum growers were the first to use it. Now it’s gradually catching on among spray chrysanthemum growers as well. More and more growers are attracted by the diffuse light it provides.”
“I think its effectiveness is underestimated,” Hofman adds. “We grow chrysanthemums in lots of colours and I get the feeling that the intense colour is preserved better under this screen. But most chrysanthemum growers only grow white and yellow. Those colours are less sensitive to solar radiation.”
Whether the screen makes for faster growth, a more uniform crop or a heavier chrysanthemum, the two find it hard to say. Habraken: “Compared to the Solaro aluminium summer screen, the white Harmony screen does a better job. The research shows that Solaro absorbs some of the light, which makes the screen hot. The new screen absorbs virtually nothing at all, and that keeps the greenhouse one or two degrees cooler.”
“In our nursery the effect is difficult to measure because we don’t have anything to compare against,” the grower says. “But we do have less delayed growth in summer. We used to notice delayed growth in plants on extremely hot days, but since we have been closing the screen on those days, it has been happening less. That’s money in the bank.”
The screen also yields results in winter. “If it’s snowing or if it’s a dark day, I close the screen to keep the temperature in the greenhouse up. So I can reduce my pipe temperature by as much as ten percent. That saves energy.” Habraken agrees: “Our research has definitely shown that the screen can deliver energy savings of between 15 and 20 percent.”
Pleasant working environment
The only thing the chrysanthemum grower did not take into account in his choice is soiling. “The screen has not been as white as it used to be for a while now. Soil preparation work and fork lift trucks generate a lot of dust which settles on the screen and reduces diffuse light radiation. Next time I would opt for a slightly lighter screen to compensate for this.”
But they will definitely be using this kind of screen again next time they build. “Apart from all the benefits for the plant, one of the most important aspects is that it makes the working environment more pleasant. When we are working in the greenhouse, we can now close part of the screen and stand in the shade without impacting too much on the quality of the crop. It’s wonderful working in the summer with the screen closed and a light breeze blowing below it.”
A new diffuse climate screen gives 32% more light to parts of the crop shaded by the greenhouse structure compared with the classic variant. What’s more, the light is more evenly distributed so there are fewer variations in the light level. Although it’s difficult to attribute all the positive effects on the plant to the screen without a comparison, growers are seeing improvements in aspects such as colour intensity and growth. But most importantly, perhaps, it makes the greenhouse more pleasant to work in.
Text and images: Marjolein van Woerkom.