“We fine-tune the amount of water to the plant’s energy supply”

“We fine-tune the amount of water to the plant’s energy supply”

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.


Wide-ranging seminars, innovations and new pavilions at GreenTech

Wide-ranging seminars, innovations and new pavilions at GreenTech

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.