Using Leds To Improve Quality
The Dutch greenhouse chrysanthemum area is estimated to be somewhere between 500ha and 600ha. Five of these belong to Rubens. Located near the Dutch town of Heerhugowaard, an hour north of Amsterdam, the family run business has grown chrysanthemums for over 50 years.
With the black-out screens closedand the far-red lights on.
I met up with the boss, Martien Borst, location manager Peter Ootes, and Patrick Casteleyn, who is in charge of global sales at LED supplier MechaTronix (MTX), to find outa bit more about the benefits that spectral control offers in chrysanthemums.
Mr Borst, who is both well-travelled and enthusiastic, initially spoke about a trip to South Africa many years ago to ascend Kilimanjaro. Taking weeks of preparation and training,it quickly became clear that one of his main challenges since accomplishing this goal has been to produce the perfect chrysanthemum.
For example, Rubens is one of the top three growers in the country when it comes to biological pest control and resilient cultivation. Also, a new research project in one areaof the greenhouse uses an infra-red camera to closely follow everything that flies at night. Think of it in terms of an early warning pest detection system.
Chrysanthemum is a short day plant, and only forms a flower bud when the days become shorter. Rubens grows the crop 12 months a year requiring strictly regimented periods of dark and light.
“Creating an artificial long day period means that we need grow lights year-round,”comments Mr Borst, who explains that lights are used during the long-day period for the first one to two weeks after planting the cuttings. This is followed by a short-day phase when plants are kept in the dark for 12 hours a day, even in summer, for flower bud formation.It depends on the variety and time of year, but it can take anything from eight to eleven weeks from planting before the flowers are harvested.
The 12-hour lighting period depends on the time of year and can vary from 4am to 4pm in the winter to 8am to 8pm in the summer. The nursery has two greenhouses (2ha built in 1997 and 3ha in 2007) and the grow lights needed inside both were initially HPS fixtures. Towards the end of last year the 1000w HPS (120mmols) luminaires in the newer 3ha structure were swapped for 1000w MTX CoolStack Boost Dual units.
The nursery owner previously studied the luminaires for three years, and closely followed what other chrysanthemum growers were doing. “Up until 2021, the majority switched to a hybrid system of swapping half of their HPS fixtures for LEDs,” he says. “For me to have done this I would have had to rewire everything and build a completely new infrastructure.”
He had no plans to install a pilot LED project. “This makes no sense to me with a crop in a continuous 10-week cycle.” In 2021, they arrived at the situation that they needed to take steps, and early last year an order was placed for 1,716 CoolStack LED units. Using the same connections, it took just 10 days to remove all the HPS fixtures and plug in the new 1000w LED ones.
The Dutch chrysanthemum grower is working with the MTX-made CoolStack Boost Dual LED top lights for the first time this winter.
From left to right: Patrick Casteleyn, who is in charge of global sales at LED supplier MechaTronix, Martien Borst and location manager Peter Ootes.
With 23 years at Rubens (last four years as manager), Mr Ootes says it was then a case of learning how to grow again. “Everything changes,” he says. “For example, the LEDs almost doubled the light levels, but then with just one third of the heat.” This is not radiated heat but convection, sowe had to increase the temperature in the heating pipes to compensate for this.”
Far-red for plant stretching
Chrysanthemums is a crop with a lot of leaves, and the low light levels during the Dutch winter can lead to yellowing of the lower ones. With this in mind, a big feature of the latest CoolStack LEDs is spectral control. This provides the possibility to switch off all the colours, with the exception of far-red, to stretch the plants.
All other LED colours are switched off 20 minutes before theend of the 12-hour lighting period. They started with this onNovember 1, 2022, and continued up until early March.
We timed our visit to see the switch from the full colourspectrum to far-red. This changes as the days lengthen, but the time of our visit was at 5pm. The black-out screens are closed as fast as possible to keep the warmth in during the winter (as late as possible during the summer to keep the heat outside), and the contrast to when the lights switch to far-red only, is huge. The greenhouse was dark to the naked eye, and my camera certainly struggled with the light.
Fortunately, the grower left the black-out screen in the lastsection of the greenhouse open for a few extra minutes to allow me to better study the lamps. The bay width in the 3ha greenhouse is 9.6m. Each one is 117m long and there are 72 luminaires per bay.
Rubens produces 13 to 14 million stems a year. Large volumesend up in the extended east European market. The UK is another important market.
The nursery has tagged a dedicated plant in each bay to record the change in stem length. “It depends on variety, but in one section this increased from 3cm to 12cm in a week with 20 minutes of far-red a day,” says Mr Ootes. “Elongating the stems during the darkest period of the year results in a better climate inside the crop and healthier plants and leaves and a higher quality product. Also, far-red is allowing us to stretch the plants without using chemicals.”
In fact, far-red is not just beneficial on stem length, but alsoon the energy bill, with the far-red LEDs using just 50w (5%) of the installed power. “It costs nothing, but results in a huge difference in stem elongation,” confi rms Mr Borst.
However, perfecting the system is not easy. “All Dutch chrysanthemum growers working with far-red only continue to learn every day. Every greenhouse is different. We have to get it right. The ideal stem length is somewhere between 70-80cm. Anything we grow longer than this we have tothrow away. Also, far-red provides us with the possibility to infl uence stem weight.”
White and yellow are popular spring and winter colours. This picture was taken just before the black-out screens wereclosed. The lamps are in the far-red only mode.
Research centres have acquired a lot of knowledge with LEDs in chrysanthemums, but Mr Borst reckons that high energy prices are forcing Dutch growers to do their own research and that they are not far behind. “A lot of Dutch growers replicated official research work this winter.”
The far-red aspect is interesting, but Mr Borst reckons that the game changer with LEDs in general is that they are dimmable. “This provides us with the possibility to dim the lights when energy is expensive and increase it when it is cheaper. We need to find the right balance, which I feel is more important than production/sqm. This requires a change in mind set.”
With plans to swap the 1000w HPS lights in the older 2ha greenhouse for the same MTX fixtures this summer, the grower would appear to be comfortable with this change in mind set. He is also keen to install energy screens. The plan is to open the black-out screens mid-morning during the winter, but keep the energy screens closed. The thinnest one they have in mind has a natural light transmission of around 85%.
Rubens is part of a group of in total 13.5ha of chrysanthemum production which was founded by Martien’s father and his uncle, initially growing carnations. This was later followed by other crops, some seasonal, including liliums and Solidago, they have always grown cut flowers. They switched to year-round chrysanthemums when moving to the current site in 1997. Working initially with 2ha of glass, this was later extended to 5ha. While independently managed, Rubens is integrated with Bovebo, which has 8.5ha of chrysanthemums in Hensbroek, a village midway between the Dutch towns of Alkmaar and Hoorn.
The far-red lights use just 50w (5%) of the installed power. “It costs nothing, but results in a huge difference in stem elongation,” comments Mr Borst.
Lights in chrysanthemums
Most Dutch chrysanthemum nurseries work with grow lights, but MechaTronix (MTX) reckons to be the only one to provide the possibility to use just far-red with its newly designed CoolStack Boost Dual 1030watt.
“Dutch growers lead when it comes to LEDs in the crop,” says Patrick Casteleyn, who is in charge of global sales at MTX. “Some 20 growers currently have the same possibility as Rubens to play with far-red. Plusthere are another 20 or so nurseries with a hybrid HPS/ LED system.”
The MTX engineering team started the development work on the two-channel luminaire early 2021. Tests with far-red showed that they could influence plants (including cucumbers, chrysanthemums, lilies, roses, lettuce, lisianthus, orchids and anthuriums) during the different growth stages. “Each one reacts in a different way so it was important to develop something what could be used commonly and flexible for all,” comments Mr Casteleyn. The result is a 1030w basic spectrum of red/blue/green/white, plus, 100w of far-red separately. “Each channel is dimmable via the growers’ climate computer.”
He reckons that the added value of the luminaire is the dynamic LED driver. “When the second channel of far-red is not used we retain the 1030w basic spectrum. When the second channel is used we have a basic spectrum of 930w and 100watt of far-red. Interest in this two channel control product is huge, so at the moment we are signing some nice new contracts worldwide.”
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