Linflowers is the first chrysanthemum nursery in the Netherlands to have diffuse glass. It was a difficult choice because apart from a lack of commercial experience no research results were available either. The brothers Van Tuijl particularly wanted high light transmission and received diffuse light as a bonus. So far their experiences have been positive.

As you walk around the new greenhouse of Linflowers, Bommelerwaard, in the middle of the Netherlands when the sun is shining it’s obvious that the glass provides super light transmission. The light level is so high that sunglasses are almost essential when harvesting the white flowers.

Afraid of scorching

“I wasn’t very positive about diffuse glass. I thought it was more for vegetable crops. Although you know you might achieve extra yield if the light penetrates further into the crop, I expected the extra production to come mainly in the summer and for a chrysanthemum grower that’s of no value,” says David van Tuijl. However, the greenhouse builder remained insistent. He now has low-iron glass with an AR-coating that allows in 5% more light. “Now that is interesting. And in terms of price, having opted for tempered glass it made no difference if we chose to have it diffuse or not. But we thought it might be beneficial because we were a little afraid of scorching under so much light.”
David, together with his brother Rochus, owns Linflowers which comprises three locations (15 ha in total). With help from a restructuring scheme in the Bommelerwaard region in 2014 they dismantled one location to make more room for colleagues. In exchange they could demolish an old nursery in Zuilichem and construct a new greenhouse of 7.6 ha. They grow 15 different kinds of spray chrysanthemums for the East European market which prefers a heavy quality.

Is extra investment worth it?

Even after they were offered the diffuse glass at no extra cost they still didn’t make the decision immediately. “We turned the question around: What were the disadvantages? Together with consultant Theo Roelofs and the glass supplier we spoke to Tom Dueck, the diffuse expert at Wageningen UR Greenhouse Horticulture.”
But there weren’t any research results available for chrysanthemums. Indeed together they came up with more questions: You make the light softer but you lose a little through the diffusivity. What happens then? The low-iron glass allows in as much extra red as blue light. Would the chrysanthemums become shorter if you make the light diffuse, or not?
By using a growth model, chrysanthemum specialist Theo Roelofs of DLV Plant, tried to determine if the extra investment in the glass with high light transmission (compared with ordinary float glass) could be economically justified. He was able to translate 5% more light into 1.2 kg/m2 of chrysanthemums or 15 stems/m2 or 4 g/stem. “We didn’t take into account the diffusivity. That will certainly have a large effect in the winter but due to a lack of data we assumed that to be neutral,” says Roelofs.

Took the gamble

The calculation brought some comfort but still Van Tuijl had three scenarios in his head: “Firstly, you achieve five per cent more growth. That is okay. Secondly, there is no extra growth and you lose your investment. The third possibility is that you have peculiar crop growth. Then you have a real problem because removing the glass is not an option.”
In addition, there was still the question about how light transmission will develop over time. “Vegetable growers who installed the first types of diffuse glass are facing this now. The glass becomes dirtier than expected because it’s less easy to clean and therefore less light than expected enters the greenhouse,” says Roelofs. In the meantime the way in which the glass is made diffuse has changed making dirty glass much less of a problem.
In short: all the evaluations did not provide a clear picture for chrysanthemums. “In the end we simply took the gamble,” says Van Tuijl. The glass is supplied by Horti Glass. They opted for a relatively low haze, namely 50%, to minimise the light loss that occurs when the glass is made diffuse.

More yield than expected

They have already produced a few crops and therefore have gained some experience but it is still too early to give a balance for the year in terms of kilos. “However, I am quite positive. If I had to make the decision again today I would do the same,” says the grower.
The brothers can compare two of their own locations although they have to keep in mind that the soil structure of the new nursery is different and there were some running-in issues. So with some reservations, he says: “So far we’ve managed to achieve well above five per cent extra yield and the weight is better than expected. We target the East European market so the stem weight has to be well above 80 gram; during the winter we were regularly hitting 90 grams.”
This provides opportunities to adjust the planting density or speed of production. They decided to play safe with the first crops. They maintained the same growing speed and the consequence of this appears to be a heavier crop. Visually the crop is just the same as at the other location and the way of inhibiting growth is the same.
In principle the energy consumption should be more favourable because more light enters but the grower has not noticed any distinct differences. “I am particularly pleased with the extra growth,” he says.

Screen

A diffuse roof does allow you to be more dynamic with the cultivation strategy, says the crop advisor. Even though no one else has experiences with chrysanthemums under diffuse glass, diffuse coatings are being applied. “When Redufuse was launched, we noticed that the types that are sensitive to wilting quickly, such as Bacardi, had less of a problem when the sun suddenly broke through. It offers new possibilities. A number of nurseries have already fitted very clear glass. These growers were noticing that the crop wilted suddenly and they had the feeling that growth was below optimal. Then a diffuse coating offers a solution.”
Furthermore a diffuse roof makes it possible to use the black out screen as a shading screen. “If you close it partially under a normal roof you get a sharp separation between the light and shadows. With a diffuse roof the difference is much less,” says the advisor. In the mean time two other chrysanthemum nurseries have also decided to fit diffuse glass with high light transmission for the same reasons as Linflowers. These are currently being built.

Summary

Despite lack of research and commercial experience chrysanthemum nursery, Linflowers, opted for diffuse glass, although this was just a bonus on top of high light transmission. On balance it’s calculated to bring 5% extra yield. It has lived up to expectations during the first six months. Also, the diffuse roof gives the opportunity to grow the crop in a different way.

Text: Tijs Kierkels. Photos: Wilma Slegers