Home Posts Tagged "Next Generation Growing"

Next Generation Growing

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In Next Generation Growing, everything revolves around the needs of the plant. In the past, much of the way growers controlled the climate was based on green fingers and experience. But with the latest developments in greenhouse technology, the indoor climate has become a more complex factor. This also makes the relationship between conditions outside the greenhouse, the growing climate on the inside and the impact on plant growth less straightforward. The combination of plant monitoring and an advanced control system helps the Dutch company Van de Berg Roses to better match their irrigation to the needs of the plant.

Hoogendoorn Growth Management researcher Jan Voogt differentiates between three plant balances: the assimilate balance, the energy balance and the water balance. All three need to be in balance to achieve optimum growth. If you only factor in the energy from the sun and not the rest, then you’re not doing your job properly, he believes. He recognised that growers who work with lighting didn’t like the fact that they couldn’t input the energy they added from the lighting into the climate computer. And the same was true of the other factors that play a role in the energy balance.

In response to this, Hoogendoorn developed a new monitoring and control system: PlantVoice. This software module focuses on all three balances and takes the plant’s activity into account. Other factors apart from sunlight can be entered in this system, and irrigation is primarily determined on the basis of the energy flows. “The more factors you include, the more accurately you can fine-tune the amount of water to match the energy supply to the plant. That also gives you more control over the root environment and less unnecessary return water,” Voogt says.

First users

Van de Berg Roses has a 12 hectare rose nursery in Delfgauw, as well as sites in Naivasha in Kenya and Kunming in China. Maurice de Ruijt, cultivation manager at the company’s Dutch site, has been using PlantVoice for the past eighteen months. “We were pretty much the first users,” he says. “We used to irrigate based on our outdoor sensors which measured the amount of sunlight. We use a lot of artificial light here, so that wasn’t particularly helpful. We told them that we wanted to irrigate based on the PAR sum. The new module is a much more reliable measure of conditions in the greenhouse.”

PAR sum

De Ruijt had already been indirectly watering based on the PAR sum via the LetsGrow system, which had given him quite a bit of experience in this method of irrigation. He uses the measured PAR sum to determine when to start irrigating. Since he started using the new software module, he has started irrigating at the point when he measures a radiation sum of 10 mol/m2 after the last cycle. He knows from experience that the slab will have dried out by around ten percent by then. This point is reached between 2 and 6 am. He doesn’t want to start any earlier or later.

De Ruijt: “The start time can vary by a couple of hours. There could be various reasons for these variations. We can switch our lighting system on in three stages: 33, 66 and 100 percent. Sometimes we use 66 percent for a while.” What’s more, the outdoor conditions can vary after they have stopped irrigating. “Like if it’s a cloudy day but the cloud cover breaks up after you finish watering, and then you have an hour or two of sunshine.”

He waters around eight to ten times a day, stopping at 3 pm. De Ruijt still decides how often to water based on the PAR sum. For the time being he isn’t using any other factors such as the energy given off by the heating pipes to decide when to start watering, as that is more complicated and the amount of energy is negligible.


Also important, of course, is what this method of climate control can deliver. “We can see that the plants have nice white roots. The crop is healthy and we’re getting better yields.” De Ruijt won’t reveal any more than that. Using the module to control irrigation is a big step in itself, but the company has also made other changes to its irrigation regime. And this, too, is part of a greater whole. “It’s a great tool to work with. It was tricky to find the right settings to begin with, but now that we’re used to it, it works really well.”

More reliable trials

Bram van Haaster, trial manager at Wageningen University & Research in Bleiswijk, the Netherlands, has been using the new module since the summer. He looks after the vegetable, flower and pot plant crops in the trial greenhouses. For the research it’s important to keep the climatic conditions around the plant as stable as possible and to only allow the factors being studied to vary.

He used to control irrigation based on outdoor radiation, the amount of drain water and instinct. That was tricky because the percentage of drain water fluctuated. Now he keeps an eye on the energy balance using sensors and data from the climate computer. He measures the amount of radiation in the greenhouse with a PAR sensor above the crop. He can input into the computer how much energy he is adding via the pipes and whether or not he is screening. In this case, energy input from the heating pipes is left out of the equation as it is a constant, low factor. “If the heating were to fluctuate, we would need to take that into account,” Voogt adds.

As a control, he uses an IR sensor that measures the plant temperature. Any rise in the plant temperature is a sign that the plant is not transpiring enough. In that case, he needs to adjust the irrigation or reduce solar radiation levels.

First experience

Van Haaster gained his first experience with this system in the summer, in a pot plant trial in which various substrates were tested alongside each other. Now a tomato trial under LEDs is underway, comparing various varieties and studying the effect of adding, or not adding, extra steering light in the form of long-wave red radiation. The light is on between midnight and 6 pm. The trial manager has been aiming for a stable drain percentage in both trials.

At this time of year, van Haaster mainly uses the PAR sensor to measure the light from the LEDs. “The outdoor light is around ten percent at best at this time of year. The increase in joules is easy to track on the computer,” he says.

On the screen he points out a neat, constant line representing the amount of drain water. Since he started using the module, the drain percentage has been stable. “If you don’t have to do much adjusting afterwards, that means you have got the settings right,” he says. “The root zone is nice and stable, both in terms of water content and EC. That’s good for the research, but it also benefits growers. You become more aware of your plants’ needs so you can get more out of them.”


With recent developments in greenhouse technology, the indoor climate has become more complex and more factors are influencing the plant’s energy balance. And that in turn impacts on the water balance. A software module is the answer. PAR sensors inside the greenhouse measure the amount of radiation in the greenhouse, and other energy factors such as the heat from the heating pipes, the screening factors of screens or coatings, diffusion and ventilation factors can be added in. Altogether they produce a better picture of the plant’s energy balance and therefore its water requirement.

Text and images: Marleen Arkesteijn.

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The third edition of GreenTech Amsterdam, which runs from 12 to 14 June, will be twenty percent bigger than the last edition in 2016. By the end of March, ninety-seven percent of the available stand space had been allocated. According to the organisers, RAI Amsterdam, this proves that the event has really made its mark as an international platform for the horticultural sector. As in previous years the trade fair will feature a wide range of seminars, some of which will be held in the new themed pavilions.

Awaiting the international delegates this year will be at least 450 exhibitors, including world market leaders and innovators in horticultural technology and a full compliment of greenhouse builders, horticultural suppliers, machinery companies, potting compost and substrate producers, lighting vendors and seed suppliers.

Knowledge programme

Ever since the first GreenTech in 2014, the organisers have aimed to make this trade fair stand out from other similar events by offering a wide-ranging knowledge programme. The upcoming edition will therefore feature more than 80 seminar sessions spread over three theatres: Food & Flower Crops, Climate, Water & Energy, and Trends & Innovation.

In addition to the Vertical Farming Pavilion introduced in 2016, this year’s event features two new pavilions: the Precision Horticulture Pavilion and the Medicinal Crops Pavilion. The Precision Horticulture Pavilion will showcase censoring technology, cameras, robotisation and digitisation, while the Medicinal Crops Pavilion will focus mainly on technology for medicinal cannabis production, a subject that will also feature in the knowledge programme.

Following its success two years ago, the Vertical Farming Pavilion is to make another appearance this year. “In 2016 we embraced the discussions going on within the sector as to whether this would be the future of global food production,” exhibition manager Mariska Dreschler says. “The fact is that it is a very interesting development from a technological point of view. In this pavilion we explain exactly what the technology entails and we will also be demonstrating some cultivation systems, reflecting some of the many new initiatives in this field in recent years.”

Objective dialogue

The informative theatres are partly made possible by some of the international heavyweights of the horticultural sector, including Koppert, Biobest, Svensson, Hoogendoorn, Hortimax, Priva, Philips and Alumat. “We are very proud that these companies and organisations have expressly affiliated themselves with this initiative,” Dreschler says. As of early April, it is hoped that even more companies will contribute to the knowledge sessions. “Their knowledge and expertise make these sessions a must for any grower. Together we will produce an outstanding programme that shines the spotlight on the international grower’s day-to-day practice.”

Advisory Board

A committee of experts is advising the organisers on the themes, subjects and speakers for the knowledge programme. This Advisory Board was set up to ensure an objective dialogue on subjects of topical interest within the rapidly evolving horticultural sector.

The members of the Advisory Board for this edition are: Sjaak Bakker, chair (Wageningen University & Research), Aad van den Berg (Delphy), Gabrielle Nuijtens (Top Sector Horticulture & Propagating Materials) and Michael Ploeg (Dalsem). “We are delighted to have such a prominent Advisory Board at our side,” the exhibition manager says. “This way we can ensure that the knowledge programme is made up of sessions that will challenge growers and encourage them to push the boundaries. The Board’s expertise and experience are of inestimable value to our programme.”

The Organic Farmers Fair

This year GreenTech will also be the venue for The Organic Farmers Fair (TOFF). For three days, the spotlight will be shone on knowledge and innovation in organic agriculture and horticulture. This part of the event came about as a result of a collaboration with IFOAM and FiBL and has been made possible partly thanks to five partners: Bejo, DCM, Steketee, Koppert Biological Systems and Delphy. Wageningen University & Research is also involved as a supporting partner.

The organisers have put together a high-quality knowledge programme on organic farming, with in-depth coverage of the most relevant issues in this field. TOFF is aiming to become an international meeting place for organic growers as well as conventional growers considering the switch to organic.

Forefront role in organic farming

The Netherlands plays a leading role in the technical development of both organic and conventional agriculture and in increasing and improving production. The domestic market grew by 11.5% in 2015 and by 13% in 2016, to around €1.5 billion, with exports of €1.2 billion. The total EU market exceeded €30 billion in 2016. Annual turnover in the world market is heading towards the €100 billion mark.

Markets are developing fast, but so is organic farming technology, with several thousand companies supplying products and services to organic farmers across the globe. So it was a logical step to combine the momentum of the TOFF event with GreenTech 2018 at RAI Amsterdam. Delegates can also take the opportunity to visit some innovative organic farms and demo fields in the Netherlands.

The future of horticulture

The GreenTech Summit takes place on 11 June, the day before the exhibition opens. This seminar offers 750 investors, breeders and growers a unique opportunity to network and to take part in a high-quality programme of sessions. Under the title “The future of horticulture – insights for the next decade”, visionaries and experts will be sharing their vision of the world of horticulture over the next ten years.

The summit will be hosted by stand-up comedian Greg Shapiro and will feature speakers including Stijn Baan (Koppert Cress), Martin Koppert (Koppert Biological Systems), Mike Vermeij (BOM Group) and Christian Kromme, futurist, speaker and author of “Humanification”. Kromme will help unlock the DNA of innovation and will explain how to apply it in our horticultural businesses and our daily lives.

Flower Trials

The direct tie-in with the Flower Trials breeders’ event delivers great added value, the exhibition organisers believe. “The two events were held simultaneously in 2014, and there was some mutual interaction in 2016. We will be continuing this collaboration this year,” Dreschler says.

A greenhouse is to be built in the exhibition hall, where ornamentals breeders taking part in the popular open days will be presenting their products. Vegetable breeders’ crops will also be on display, ensuring that this key greenhouse horticulture segment is also represented at the show. The breeders’ pavilion looks set to be an impressive experience and a good starting point for the visits to breeder organisations.

Innovation Award

One of the highlights of the first two editions of GreenTech was the much coveted Innovation Award, which attracts more and more entries each time. This award forms part of the exhibition’s efforts to stand out internationally in the areas of knowledge transfer and innovation. “We want to showcase all the latest trends and developments,” Dreschler says. “I would even go so far as to say that no other horticultural trade fair in the world shines the spotlight so emphatically on its innovations.”

Annual international trade fair

Dreschler says she will regard the 2018 edition as a success if it gives rise to synergies between exhibitors and delegates that lead to potential business. “We will once again use every indicator at our disposal to gauge satisfaction levels among the various target groups. If delegates tell us that they have learned something new and will come back to Amsterdam again next time, then we’ve done a good job.”

Note that the fourth edition of GreenTech will not be taking place in 2020 but in 2019, as the organisers have decided to turn it into an annual international trade fair.


The third edition of GreenTech takes place in Amsterdam in mid-June. This year’s event will be bigger than the last one in 2016, both in terms of floor area and delegate numbers from the Netherlands and abroad. This time there will be even more focus on knowledge transfer and innovation: various themed pavilions will highlight topical issues in international greenhouse horticulture, and an independent Advisory Board will be keeping a close eye on the quality of the knowledge programme. The organisers have decided to switch to an annual event from 2019 onwards.

Text: Roger Abbenhuijs.

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In Next Generation Growing (NGG) we’re always talking about balances: water balance, fruit balance, energy balance, etc etc. And in sweet pepper production we’re constantly monitoring light input with the aim of keeping the plants in balance. Wouldn’t it be great if we could shine the lights on them for a week every now and again. Just to keep setting going a bit longer or to get your peppers to market a bit earlier than your competitors. But when we do a cost/benefit analysis, lighting seems to lose out.

When it comes to selling our produce, we always aim for consistency for our customers. After all, we want to be able to supply them with the same number of trailers of sweet peppers of uniform quality every day so they can keep their supermarket shelves full. Wouldn’t it be great to get slightly more fruit weight sometimes. To fill up those packs properly, or to be able to pick those last few fruits, with the help of a little light. Fruiting vegetables are expensive in winter but you can’t install lights just for that.

In winter we’re also looking for ways to make the best use of our staff. The reality is that at the moment we really have to motivate our casual staff to come back again after the winter dip. Every year it’s a challenge to get them back in the greenhouse refreshed and at the right time and to get them to work with the same mindset as they had when we finished three months earlier. But you can’t switch your lights on just for that either.

As members of the circular heat networks in our growing area, we all want as much heat as we can get in the dark months. Everyone has plenty of heat in summer but not enough in winter. Waste processing plants aren’t about to start saving up their waste so that they can burn it in the winter and supply the heat to growers. But anyhow, the situation where you have the same demand for heat all year round helped by extra light from above (lighting) in the dark periods is still a long way off.

So why don’t we take another look at the options and switch to lighting? Not just for sweet peppers but for other fruiting vegetables and ornamentals as well.

Maikel van den Berg
Sweet pepper grower in The Netherlands

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Hans Houben’s initial reason for trying out Next Generation Growing was to save energy. “But that shouldn’t really be your main objective: you need to focus on the plant,” the cucumber grower says. This has led to a higher 24-hour temperature, growing with the light, more screening and adjusting for outgoing radiation. Oh, and lower gas bills too.

Every year is different when you use the Next Generation Growing (NGG) method. You keep taking one step further and all of a sudden you’ve created a completely new way of growing. “I am always very keen to keep up with the latest developments, but to begin with I was quite sceptical. It all sounds very logical but it takes courage to do it. Right now I’m starting venting on the wind side, for example. It is working out well: you get a much more even climate and it’s easier to keep the humidity at the right level. But I really wouldn’t have done it this way two years ago,” Hans Houben says.
His screening hours have also increased: he is now screening twenty per cent more than in his second NGG year. “During the first couple of years you tend to be a bit wary of doing things this way. Before I started I used to mainly keep an eye on relative humidity, but now it’s all about absolute humidity, humidity deficit, vapour pressure and outgoing radiation.”

Back to the plant

Hans and Carla Houben’s cucumber business Mellantas in Sevenum (4.7 ha) in the south-east of the Netherlands is on its third season of high-wire cucumbers. At their old site they had two crops of cucumbers per year, followed by autumn tomatoes. After moving to their new location they introduced high-wire cultivation with two crops per year, first Topspin and then Kurios. The plants grow in rockwool that lies on the ground.
Gas consumption is currently at 28.5 m3/m2 for production of 230 cucumbers per square metre. A traditional crop would use 34-35 m3/m2 for 180-195 fruits. “The power of Next Generation Growing lies in the fact that you are going back to the plant,” Houben says. “We have started growing more quickly, with a higher 24-hour temperature, but we keep the plant load at no more than 6-7 cucumbers per plant. From 11 am onwards we allow the temperature to get higher than before, light permitting.”

Hotting up

For example, with 1,000 watts of incoming radiation the 24-hour temperature is 21.5ºC, and with 500 watts it is 19.3ºC. In his first two years of NGG, Houben allowed an extra 1.5ºC per 1000 joules of incoming radiation over and above the basic temperature of 18ºC. Now it is 2.5 to 3ºC extra – so quite an increase. He achieves this with a combination of heating, screening and ventilation.
“An extra 1.5ºC saves more energy, of course, but it makes the crop more sluggish. When it’s sunny we want a higher temperature, preferably 28ºC after 11 am rather than 25ºC, light permitting.” Before 11 am he aims to achieve a moisture deficit of 1.5-2 g/m3 to activate the crop; after that he works up to a higher temperature in a gradual line. “I used to turn the temperature down sometimes if there was a lot of light. But I don’t do that any more. You can tell by the top of the plant whether you are doing the right thing. If it is getting too thin, the 24-hour temperature needs to come down.”
If the temperature is higher during the day, the night temperature can be reduced slightly, although it is the overall 24-hour temperature that counts. Less use of minimum pipe prevents excessive evaporation and limits night-time energy consumption. Incidentally, the main source of heat is the grow pipe, which is always level with the fruits, and not the pipe rail.

More outgoing radiation

Over the past few years the grower has started screening twenty per cent more to limit outgoing radiation. He uses a very light Luxous energy screen from Svensson which only screens out twenty per cent of the light. A radiation meter (pyrgeometer) on the roof helps control the screens. There is also a thermal camera pointing at the crop. This isn’t connected to the climate computer but is used as an additional adjustment tool. Houben demonstrates how it works on the computer screen. “This morning there was a rain shower just after we opened the energy screen. You can see on the thermal image that the temperature at the top of the plants dropped to 15.5ºC at that point. You want activity but the tops of the plants are cold. So I closed the screen again and within ten minutes the temperature at the top of the plants had risen by 4-5ºC. That’s because you are eliminating outgoing radiation.”
The principle is simple. When outgoing radiation is higher than what is coming in, the screen is closed, even on a warm summer’s day. “In that case you close it ninety per cent. Then you can control the temperature easily and control outgoing radiation at the same time,” he explains.

Dehumidification technology

The numbers always add up. For example, if there is 200 watts of radiation coming in, the screen blocks out 40 watts of that. But with a clear sky, outgoing radiation from the crop soon reaches 80 watts, and because that is more than 40, the screen has to be closed.
Houben has invested in a pyrgeometer, a thermal camera, a leaf temperature sensor and an extra sensor unit above the screen, but not in air handling units, extra fans or a second screen. “I could save an extra 2-3 m3 of gas with a second screen, but then I’d need a dehumidification system as well. The maths wouldn’t necessarily work then. So we decided not to do that just yet. We are waiting for dehumidification technology to move in a clearer direction,” he says.


With the experience he and other growers have gained, Houben sees potential to improve the system even further. “There is definitely scope to optimise the light/temperature ratio. You might be able to grow even faster with more light. If you can pluck up the courage, you could turn the temperature down more in the evening because you would still be achieving the 24-hour temperature, and that’s what counts. So an extra pipe during the day and not at night. But you could even raise the 24-hour temperature, which would enable you to maintain a higher temperature at night and make better use of the screen. And on sunny days you could also extend the day by switching to the night temperature later.”
Houben is also trying to gain a better understanding of the minimum level of evaporation needed at night. He is very happy with the knowledge shared on the LetsGrow platform. “I am learning a huge amount by looking over other growers’ shoulders. You don’t have to find it all out for yourself. You can see exactly what time other people open their screens and what that achieves. Next Generation Growing is really still in its infancy. You can get much more out of it if you focus primarily on the plant.”


High-wire cucumber grower Hans Houben is heading ever further down the path of Next Generation Growing. He has started screening more and keeps an eye on absolute humidity, humidity deficit, vapour pressure and outward radiation levels. His 24-hour temperature is up and it could even go a little higher. He is doing all this with one screen and no air handling units or extra fans.

Text: Tijs Kierkels. Image: Wilma Slegers

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Tip burn, or marginal necrosis, is a long-standing problem in tomato cultivation which occasionally rears its head in the new strategy of Next Generation Growing (NGG). What would be better than to solve this phenomenon with properly adjusted fertilisation? Dutchman Wim Voogt has investigated the influence of chlorine and iron polyphosphate on calcium uptake. To date, appropriate climate measures combined with the right variety choice have proved to be the best remedy.

Calcium, the mineral that is essential for good cell development, has an annoying trait: it can’t move through the plant of its own accord. This nutrient is completely dependent on water to transport it through the plant.
Calcium deficiency causes physiological defects such as internal browning in lettuce, tip burn in tomatoes and ornamentals, or even fruit problems such as blossom-end rot. These phenomena are directly associated with weak cells that have absorbed too little calcium as a nutrient during growth. Applying elements of NGG seems only to make the problem worse. That’s annoying, because an indirect consequence of this defect is that it makes the plant more susceptible to fungal diseases such as Botrytis.


Wim Voogt and his colleagues at Wageningen University & Research in the Netherlands have been working for many years on understanding the plant mechanism and the causes of deficiencies. Much is already known but new insights arise constantly.
Voogt draws on some basic principles that keep popping up in this context. “Calcium is a tricky element,” he explains. “The plant can only absorb it passively. Young, vigorous parts of plants need it to build cell walls and cell membranes. A plant cell is like a bicycle tyre. The cell wall is a rigid structure made of cellulose, pectin and hemicellulose. Calcium binds with the pectin chains in it. This makes the framework flexible.”


Calcium is transported to all parts of the plant via the tips of young roots and via the xylem vessels. This mainly happens during the day when the plant transpires, and to a lesser extent at night through root pressure. Young plant parts need calcium to strengthen their cell walls as the cells expand. But they are completely dependent on the calcium supplied via the xylem vessels. Once the mineral has arrived at its destination via the transpiration stream, it stays put. So parts that transpire the most get the most. That is why parts of the plant that are not (yet) transpiring enough don’t get enough calcium and suffer a deficiency, with the result that the newly formed cells are not strong enough.
Voogt: “So what you need to do is to stimulate xylem transport to growth points. You can do this in two ways: by facilitating transpiration or by ensuring sufficient root pressure.”
Weak cells are therefore the main problem, caused among other things by calcium deficiency. The real problems arise at times when root pressure is too high or when climatic conditions suddenly change. This will cause weak cell walls to burst or cell membranes to leak, resulting in the familiar physiological defects.

Leaf samples

Last year Voogt took leaf samples from an artificially lit tomato crop to study the mineral balance in the varieties Komeett and Brioso. The first is susceptible to tip burn whereas the second isn’t. He took samples from a leaf at the top next to the youngest truss which had not yet flowered, a leaf next to the most recent fully set truss, and an old leaf at the bottom of the plant. These showed that there was hardly any difference in calcium levels between the two varieties, meaning that the susceptibility of varieties is not directly connected with these levels.
What was striking was the massive increase in calcium levels as the leaf ages. The researcher also noticed that the calcium levels in the youngest leaves (at the top) fell in winter, but also as the plant load increased. Every grower knows from experience that tip burn occurs mainly between January and March. The samples confirmed this, since calcium levels in the foliage at this time of year are a lot lower than in the late spring and summer. In June the youngest leaves contain more than twice as much calcium as in December. An old leaf contains ten times more calcium than a young top leaf, both in summer and in winter. And that’s quite a difference.

Modified nutrient solution

The study also focused on the question of whether calcium uptake could be stimulated by adjusting the nutrient solution. As it had previously been observed that chloride in the nutrients can improve calcium uptake, the NO3/Cl ratio was adjusted. In addition, a Fe-polyphosphate treatment was also applied because it had previously caused less leaf curl in cucumbers.
Compared with a standard nutrient solution, the effect both modifications had on tip burn was quite disappointing, with the researchers seeing no difference in the number of affected leaves.

Climate shock

With this in mind, Voogt decided to take another look at the climate settings, which have more effect on the development of tip burn than other measures. NGG sometimes leads to situations that tend to exacerbate the problem instead of preventing it.
NGG was originally conceived as a more energy-efficient method of growing. So minimum pipe is often dispensed with, RH can be higher and the humidity deficit is low. What’s more, greenhouse air contains a lot of CO2 so the stomata are not fully open. Due to the low levels of transport via the xylem vessels, not enough calcium reaches the new growth so the cells are weak. If this is followed in spring by a situation requiring ventilation, a high humidity deficit will suddenly occur. The leaves start to transpire and the root pressure can’t keep pace. This shock puts the plant under stress.

Short nights

The trend of lighting the greenhouse for ever longer periods of time results in plants getting fewer hours of night-time rest. This allows less time for enough calcium to reach the new growth, as night-time transport happens partly via root pressure. As a result, the parts of the plant that don’t transpire much during the day get less calcium. These are the young shoots and leaves where new cells are made and where cell expansion occurs.
In addition to the humidity stress referred to earlier, internal moisture stress (root pressure) can also sometimes be so high that weak cells can’t take the stress and burst. This sounds like a contradiction in terms, since root pressure is supposed to prevent cell weakness by supplying the cells with sufficient calcium, but it happens because the period of weak cell development does not run in parallel with the occurrence of the symptom, i.e. cells bursting.
Voogt: “The main conclusion that can be drawn from this is that transitions in climate must take place very smoothly. Fortunately, the focus in NGG is turning increasingly towards optimising the climate, with plant balances and the water balance being the key criteria. That’s much better for the crop than simply aiming to save energy.”


Variety selection and climate are the main tools for preventing tip burn, since adjusting with nutrients hasn’t been shown to help improve calcium uptake. Young plant parts are particularly vulnerable, and using NGG can make a crop even more susceptible to physiological defects. Avoiding moisture shocks is the best remedy.

Text and image: Pieternel van Velden and Wageningen University & Research.

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Good air movement in the greenhouse is increasingly important. The principles of Next Generation Growing are closed screens, limited use of the minimum pipe and good air circulation. But how do you prevent a cold dump, a draft, a relative humidity that is too high and temperature differences? Fans that bring air from above a fully closed screen into the greenhouse appear to be the most effective. Dutch growers, Wageningen University & Research and suppliers are working closely on the ‘Monitoring’ project to optimise their utilisation.

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The HortiContact Tour organisation has released its full tour schedule. On Tuesday 14 and Wednesday 15 February 2017, the two-day excursion will visit multiple nurseries and research centres, and introduce international growers to the latest developments in Dutch horticulture. The programme includes a Practical Day, and a Seminar & Exhibition Day.

On the first HortiContact Tour day (14 February 2017), participants will be visiting several growing and research facilities. The excursion will leave from Rotterdam at 8:00 hours. The first stop will be at 8:30 hours, at tomato grower Jami’s in Bleiswijk, followed by a visit to the Wageningen University & Research (greenhouse department) and the Delphy Improvement Centre at 10:30 hours. Both knowledge institutes will walk tour members through the latest developments and growing experiments.

Next Generation Growing

After lunch, the group will head for De Lier-based chrysanthemum grower Arcadia at 13:30 hours. The company opened a new greenhouse in 2015. They are Next Generation Growing and plant health pioneers. The last visit of the day will bring the group to Sion Orchids at 16:00 hours, also in De Lier. The company is renowned as an innovative producer of young Phalaenopsis plants. Sion Orchids is active internationally, on multiple continents. The day concludes with a diner.

Seminar & Exhibition Day

The second day will centre around Gorinchem, 35 kilometres from Rotterdam. At HortiContact’s exhibition premises, researchers from Wageningen University & Research will give captivating presentations: Ep Heuvelink will present on the fascinating botany world (9:00 hours), while Frank Kempkes will introduce HortiContact Tour participants to the Winterlight greenhouse; the university’s new greenhouse construction project (at 10:30 hours). A complimentary lunch concludes the morning programme.
From 13:00 hours, participants may visit the HortiContact exhibition. With an average of 450 to 500 exhibitors, it is one of the biggest and most-valued meeting platforms for Dutch Horticulture. The day will be concluded with a standing dinner reception.

Free participation

The HortiContact Tour is being arranged through a cooperation of the HortiContact exhibition organisation (hosted from Tuesday 14 until Thursday 16 February 2017 at Evenementenhal Gorinchem), Uniglobe Westland Business Travel, and In Greenhouses magazine. Through support from multiple sponsors, participation in the HortiContact Tour is free of charge. Growers from abroad will need to arrange their own travelling and hotel stays. Participants can, however, make use of the organisation’s hotel and airport transfer arrangement.

More information/signing up

Do you know growers within your international business network who might be interested in this tour? Then please refer them to the following website for more information, or for signing up: www.horticontacttour.nl.

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The Dutch greenhouse sector is continuously innovating. In addition, the nurseries and research centres are keen to share their knowledge and experiences with growers from all over the world. On Tuesday 14 and Wednesday 15 February 2017 international growers will have the opportunity to join the HortiContact Tour and see first hand the latest developments in Dutch greenhouses.

This two-day excursion is being arranged by Uniglobe Westland Business Travel, In Greenhouses magazine and the organisers of the trade fair HortiContact (Tuesday 14 to Thursday 16 February 2017 in Evenementenhal, Gorinchem). The programme broadly includes: visiting leading companies (specialised in cut flowers, pot plants and greenhouse vegetables), presentations by researchers and lecturers at renowned knowledge institutes and, of course, a visit to the trade fair, HortiContact.

Practical day

The first day of the two-day program will include visits to nurseries and research centres. One of the greenhouses that participants will visit on the first day is an innovative vegetable grower in the Bleiswijk area. Another is the chrysanthemum company Arcadia which in 2015 opened a new greenhouse in De Lier. This company is a pioneer in Next Generation Growing and plant health. Sion Orchids - also in De Lier – is seen as an innovative producer of phalaenopsis young plants. The company is internationally active on several continents.

The research facilities of Wageningen University & Research (Department of Greenhouse Horticulture) and Delphy Improvement Centre are also located in Bleiswijk. At both institutes visitors can see the latest developments and cultivation trials taking place.

Seminars and exhibition

Day 2 takes place in Gorinchem, some 35 km east of Rotterdam. The HortiContact exhibition will be the site for some captivating presentations by researchers from Wageningen University & Research: Ep Heuvelink will discuss the fascinating world of plant physiology and Frank Kempkes will present the latest university project on greenhouse construction: the winter light greenhouse.

Afterwards the group will be invited to lunch and in the afternoon can attend the trade fair. With 450 participants, HortiContact is the largest and best rated meeting place for greenhouse horticulture in the Netherlands. On both days the organisers will arrange an evening dinner.

Sign up

Thanks to the support from various sponsors participation in the HortiContact Tour is free of charge. International growers will need to arrange and pay for their own trip to the Netherlands and accommodation. However, participants can take advantage of hotel discounts and airport transfers arranged by the organisers. Transport during the two-day excursion will take place via coach. Don’t wait too long to sign up because the number of places is limited.

For more information, or to sign up, please go to www.horticontacttour.nl. Please provide background information on your career and greenhouse operation, such as size, crops and location. Suppliers, students and consultants are not admitted on the bus, likewise Dutch growers who are working in the Netherlands for a Dutch business.

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Energy efficient production according to the principles of Next Generation Growing, without any additional investment, is the aim of pepper trial being carried out at the Delphy Improvement Centre (IC), Bleiswijk, the Netherlands. Armed with two energy screens and fans the trial participants want to save 30% on energy and still achieve good fruit quality.

The main barriers raised by pepper growers to grow as energy efficiently as possible in practice are doubts about the impact on crop health and fruit quality. This therefore was the reason for running two climate trials this year with peppers, one at the Improvement Centre and the other at neighbouring Wageningen UR Greenhouse Horticulture.
The one at the IC is being carried out in an area covered with a standard greenhouse roof and two energy screens. The other trial is taking place simultaneously in a VenlowEnergy greenhouse with double glazing. The red variety Maranello was planted in both greenhouses on 7 December 2015. A Supervisory Committee, which includes four pepper growers, is following the trials closely.

Energy savings

The trial at the IC uses two transparent energy screens, namely Luxous 1547 D FR and Luxous 1347 H2no FR. The H2no property ensures that when the screen is used during the day it also allows a lot of light to penetrate even when it is wet due to condensation. In addition the area is equipped with horizontal and vertical fans and is sparsely heated. Although the energy consumption on commercial nurseries is usually about 30 m3 per m2 the trial participants are aiming for 20 m3 per m2. That is a saving of more than 30%.
Assessing the balance half way through the trial it would seem that the goal is achievable. Energy consumption is even slightly lower. Maximum use of the energy screens and omission of the minimum pipe rail therefore have a huge impact.

Screening based on radiation

The principles of Next Generation Growing (NGG) were applied during the trial. The use of the energy screens is the dominating factor. The upper screen opens when the radiation is 100 watt per m2. The second screen opens at the moment that the temperature above the screen differs by four degrees from the desired heating temperature. This small difference should prevent a cold dump.
There were moments this spring that the lower screen was still closed when the radiation was 300 to 500 W/m2. The intensive use of the screens has, from the start of the cultivation to early April, led to 14% light loss. That was difficult for the growers to get used to as they prefer to allow in as much light as possible.
“But the crop was growing to our liking,” says Rick van der Burg, crop manager at the IC. “We noticed that the room temperature was quickly a degree higher than what is usual in practice," adds Arie de Gelder, researcher at Wageningen University & Research.

Drain off moisture

At the same time the screens play a major role in the removal of moisture. At the moment that the RH becomes too high, cool dry air is supplied via the vents above the screens. The moisture is then removed to the outside via transport through the screens. Therefore the usual method of making a gap in the screen is not used,
The fans ensure a uniform temperature and moisture distribution in the greenhouse. At the start of the cultivation this was achieved by just using the horizontal fans. As the crop becomes taller the vertical fans are used too.
The trial participants are not completely satisfied with the air currents and thus the temperature distribution that occurs in the section. Bubble wrap is attached to the walls to rule out influences from outside and from the adjacent much warmer section. Because so little heating is used the temperature differences between the walls has relatively large impact. “We’ve noticed that strong air currents occur,” says De Gelder. That will be different in a practical situation.


When Van der Burg made the first assessment in mid April, it revealed that 2,500 hours of screening were with a double screen. That saved a lot of energy especially in March and April.
A net radiation sensor was hung in the top of the greenhouse. This shows how much radiation enters the greenhouse and how much radiation is emitted from the crop. The double screen in the night leads to an important reduction in the radiation emitted.

Screen out the light

As the radiation increases, the screens will be used as a tool to screen out excessive light. The greenhouse does not have a solar reflective coating. When the radiation is more than 700 W/m2 the upper light diffusing screen closes 80% and the lower screen 40%. They are positioned so that they overlap each other. De Gelder: “In this way we want to keep the humidity as well as the CO2 as much as possible at the right level."
Initially ventilation only happened when the greenhouse temperature was more than 27°C. Since the greenhouse temperature rose rapidly at high radiation it was decided to slightly reduce the temperature. Van der Burg: “We noticed that the fruits then become wet and we have to prevent that.”

24-hour temperature based on radiation

The desired greenhouse temperature is very dependent on the radiation. During dark periods the 24 hour temperature is 18.5ºC. When the light sum is 1,000 joules the 24-hour temperature should be 20.5ºC and at 2,000 joules it should be 22.5ºC. The light sum of the previous day determines the night temperature that follows.
It’s noteworthy that no minimum pipe rail is used. Heating is only used when there is a need for energy. Incidentally, plant temperature is well monitored.

Fruit quality

What is now interesting is how the crop responds to these climate settings. In particular the growers in the Supervisory Commission, who are willing to push to the limits, have been amazed at the crop condition. They didn’t expect the crop to look so good after so much screening and the subsequent loss of light. During the first setting some fruits aborted so the trial participants didn’t have to consider thinning out. The first setting started to develop a little later than in commercial nurseries but the differences weren’t shocking. Harvesting started in week 12 and by week 18 the yield was 6.10 kg/m2.
The second part of the cultivation will be interesting when the radiation rises even higher and the crop develops further. Then the emphasis will be more on the vertical temperature distribution in the greenhouse. Of course the growers and researchers are closely following the quality of the fruit. Everyone is wondering what the final fruit quality will be like and what affect the climate regime has on the total yield.


A pepper trial with NGG in an existing greenhouse in the Netherlands shows that during the first half year a lot of screening has no adverse effects on the crop or yield. Up to now it has been easily possible to save 30% on energy. The two energy screens limit the radiation during the night so the crop temperature remains higher.

Text and images: Pieternel van Velden

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Assimilation lighting has a big impact on the greenhouse climate and - when the electricity is generated on site - on the efficiency of the energy generator. Optimising the control of the lighting installation leads to a gain in both areas. Two growers and their suppliers explain how they achieved it.

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