Home Posts Tagged "CO2"


811 0

HVC is currently installing a capture installation for Bio-CO2 in Alkmaar as a demo trial for the bio-energy power plant. The Bio-CO2 will be tested later this year by greenhouse growers in the far north of the province of Noord-Holland.

HVC is the first company in the Netherlands to capture CO2 from a bio-energy power plant and to convert this into liquid CO2 for horticulturists in the region. HVC captures the Bio-CO2 directly from flue gases, thus reducing its own CO2 emissions. Linked to a bio-energy power plant, the installation will prevent approximately 4 kilotons of CO2 from being emitted on annual basis. Thanks to the Bio-CO2 greenhouse growers in this region will no longer need to rely on the fossil fuel natural gas. There is a particular need for this in hot summer weather. A single ton of Bio-CO2 will enable you to save half a ton of CO2 derived from natural gas.

Increased sustainability

The construction of the CO2 demo trial installation is an intermediate step for building a larger capture installation as a regional source of Bio-CO2 and to attain the goals of the Noord-Holland Green Deal CO2 for greenhouse horticulture companies. The external supply of CO2 is a key precondition for enhancing the sustainability of the greenhouse horticulture industry. Robert Kielstra, Director of Energie Combinatie Wieringermeer (ECW) and representative of the greenhouse horticulture companies at Agriport: ‘Capturing CO2 is a prime example of the circular economy. Although this is just a trial installation, this step will mean a giant step forward in sustainability – particularly after a scale-up – because it contributes to reducing the use of natural gas in the greenhouse horticulture industry.’

Green heat

In addition to supplying Bio-CO2 to greenhouse growers, HVC’s bio-energy power plant will also provide 4,800 customers in Alkmaar, Heerhugowaard and Langedijk with heat. The ultimate goal is to provide 15,000 households and commercial enterprises with green, sustainable heat. The bio-energy power plant, which is fired by waste wood, is in fact nothing but a huge central heating boiler for the entire region. When waste wood is burned, steam escapes which is subsequently used to heat water. This water is then transported to households and businesses in the region via heat pipelines. The cooled-down water will return to HVC, where it is heated up again.

Source: HVC. Photos: HVC/ Marc Dorleijn.

562 0

With the second crop in the Winterlight greenhouse at the Energy Innovation and Demo Centre (IDC) in Bleiswijk (NL) coming to an end, it’s time to draw some initial conclusions. The predominant feature of the greenhouse is its extremely high light transmittance.

Growers don’t only stand to gain from this in the winter but in the dark autumn months too: the 10%-plus light gain the designers were aiming for has turned out to be a reality. This not only means that all the partners involved in the project did a fantastic job, but also that the models used in the design process, such as RAYPRO, have proved their worth.
On the crop side, the two high-power crops we grew also yielded good results, despite the thrips problems we had in the first crop. With a few growing weeks to go, the tally is currently 268 cucumbers with an average fruit weight of 407 grams, bringing the total yield to more than 109 kg/m2. We are pleased with the outcome on the energy front, too. In this greenhouse, which is single glazed and has two high-transparency screens and a dehumidifier with heat recovery, we used less than 20 m3/m2 gas between the end of December and mid-November. But this did mean that we had to buy in around 13 kg of CO2.

850 0

With the second crop in the Winterlight greenhouse at the Energy Innovation and Demo Centre (IDC) in Bleiswijk (NL) coming to an end, it’s time to draw some initial conclusions. The predominant feature of the greenhouse is its extremely high light transmittance.

Growers don’t only stand to gain from this in the winter but in the dark autumn months too: the 10%-plus light gain the designers were aiming for has turned out to be a reality. This not only means that all the partners involved in the project did a fantastic job, but also that the models used in the design process, such as RAYPRO, have proved their worth.


On the crop side, the two high-power crops we grew also yielded good results, despite the thrips problems we had in the first crop. With a few growing weeks to go, the tally is currently 268 cucumbers with an average fruit weight of 407 grams, bringing the total yield to more than 109 kg/m2. We are pleased with the outcome on the energy front, too. In this greenhouse, which is single glazed and has two high-transparency screens and a dehumidifier with heat recovery, we used less than 20 m3/m2 gas between the end of December and mid-November. But this did mean that we had to buy in around 13 kg of CO2.

809 0

The focus of energy savings usually lies in technology. But the crop itself offers numerous opportunities to economise on energy consumption. Many research results are still waiting to be translated into practice.

Significant differences in energy consumption per square metre or per kilo of product regularly exist between nurseries with similar greenhouses and the same crop. These can be attributed to different views on production among the growers. One grower likes to play it safe, the other looks more into the possibilities of the plant. Within the scope of The Next Generation Growing other ways to deal with the characteristics of the crop is gaining more attention. Previous research results form the basis for this.


Transpiration is the driving force behind essential processes such as mineral uptake, transport in the plant, maintaining cell tension and development of fruits. But the plant exaggerates: In the greenhouse it often transpires much too much. This 'luxury' transpiration brings an excess of moisture into the air, which then needs to be removed. And draining off moisture always costs energy. It would be very advantageous to be able to slow down transpiration. Various studies have shown that it can be reduced by 30 to 35% in tomatoes without any cost to production.

Less minimum heat

Yet in practise, growers are still reluctant to slow down the transpiration. They want an ‘active crop’ and are afraid that root growth will lag behind. But ‘active’ means that the crop fully assimilates; this can also be done with less transpiration. And you can stimulate root growth better with a lower greenhouse temperature.
Over the last few years commercial growers have been assessing much more critically the use of the minimum heating pipe to reduce air humidity. Actually, raising the temperature encourages the crop to transpire even more. And then the windows have to be opened to lower the air humidity.
One step further than economical use of the minimum pipe is dehumidification with external air in combination with more screening. Then you control the air humidity independently of the window position. But this of course requires extra technology.

Picking leaves

A very effective means to drastically reduce crop transpiration is to pick leaves on a major scale. With a leaf area index (LAI = m2 leaf surface area per m2 ground) of 3 to 4 you already have sufficient light interception. Any number above that means you have a superfluous amount of leaf in the greenhouse.
It’s normal to pick the leaves of tomato plants but it would also be a good idea for sweet peppers too. The lower leaves only transpire and don’t contribute any more to photosynthesis. Picking could also be an option for different ornamental crops. Of course you need to consider whether the extra labour outweighs the energy savings.


In practise there are many fixed views about the necessary temperature gradient during the day. Tomato production is definitely a crop that is very dependent on the temperature strategy. But some of these opinions lead to very high energy consumption. If you heat before sunrise, when the outside temperature is at its lowest point, it costs a lot of gas. If you want to achieve a sharp drop in temperature at the end of the day, and therefore open the windows, all the heat that you’ve just put in is simply lost.

Retain the heat

The question therefore is whether the temperature gradient during the day needs to be so precise. To find out, a study compared three regimes: Heat up quickly in the morning and cool down quickly in the evening; heat up and cool down slowly; and a middle road in which the house was heated slowly and cooled down quickly. The researchers followed the crop for an entire season, critically observed by a growers group. What happened? Looking at the crop you couldn’t tell which treatment had taken place and yield hardly differed. However, the steady strategy did save energy.
For the growers group it was a question of ‘seeing is believing’. They applied the regime to their own nurseries. Seen from a plant perspective the results were not surprising: The plant responds sooner to the mean 24-hour temperature than to a specific gradient during the day. So as a grower of fruit vegetables you can easily heat the house adapted to the amount of light and keep the heat in at the end of the day. You achieve the same 24-hour temperature with less energy.


Another point is that at the end of the day leaves and fruit cool off at different speeds. The leaf temperature follows the greenhouse temperature; the fruit temperature lingers behind. The effect of this could be that the fruit attracts more assimilates. The differences are so small, that it’s hardly noticeable. Research has shown no differences in fruit weight between the different cooling strategies.
In pot plants, where the shape of the total crop is important, phenomena like DIF (the difference between day and night temperatures) and DROP (a sudden drop in temperature) can indeed affect the elongation or the compactness. Then it’s worth having a temperature regime during the day.

Light and lighting

If you look at light from an energy point of view, you arrive at two questions: How do you best utilise the natural light and when does it pay to use assimilation lighting? The answer to the first question was always: Ensure that the greenhouse has the highest light transmittance possible. Based on the research over recent years we can now add: Diffuse light almost always pays off. This light penetrates much deeper into the crop, the horizontal distribution of light is more uniform and both result in more assimilation.
The answer to the second question requires some more explanation. With respect to temperature, the plant responds to the average over the day, or over a few days. The latter forms the basis for temperature integration. With light however, there is an immediate response. At the same time, there are reasons why the plant, despite a lot of light, assimilates very little, for example, because the stomata are closed for one reason or another. It is therefore very useful to know the reason why. Then you know when the assimilation lights have an effect.


A grower can already determine the photosynthetic activity himself with instruments such as the Plantivity, but these measure just a very small piece of leaf. New methods are being developed that measure the photosynthesis (actually the fluorescence) of a square metre of leaf surface area.
A better understanding of photosynthesis can save energy because then the grower can adjust the lighting and CO2-dosing according to the activity of the crop.


A different growing strategy is a potential key to saving energy. An important part of this is to slow down transpiration. Furthermore, the precise temperature gradient over the course of the day is often not that important. The plant responds more to the average for the day (or several days). This response also offers a basis for saving energy. Finally, better utilisation of natural and assimilation light is possible.

Text and images: Ep Heuvelink (Wageningen University), Anja Dieleman (Wageningen UR Greenhouse Horticulture) and Tijs Kierkels.

689 0

Sweet peppers can manage with 800 ppm CO2 in the winter months. Supplying more than that doesn’t boost photosynthesis: in fact, the sweet pepper plant simply gets used to a higher dose, resulting in ‘lazy’ leaves. Luckily, this is easy to reverse when spring arrives. The lazy leaves are back in action after six days.

These are the conclusions of Dutch research into sweet peppers carried out in 2014 and 2015 by Plant Lighting, Inno-Agro and Plant Dynamics. The research was conducted under the guidance of the Horticultural Technology Development growers association (TTO).

Greenhouse air quality

Many growers have a free supply of CO2 from their CHP units. But finding out what the ideal dose is doesn’t feature high on their list of priorities. “It may not help, but it can’t do any harm” is often the rule of thumb. Nevertheless, Stefan Persoon, innovation specialist at Inno-Agro, has noticed that this is changing.
“First of all, we are starting to use less fossil fuel as a sector. Of the 1,650 hectares of sweet peppers in the Netherlands, 300 hectares are grown using geothermal heat or another alternative energy source. Those growers pay for their CO2, for example via OCAP (CO2 from the port city of Rotterdam), and this encourages them to do more with less. A second reason for finding out the ideal dosage is the quality of the air in the greenhouse. On the face of it, this doesn’t seem to be a problem, but measurements taken inside greenhouses reveal that the air quality can easily come under pressure. Oddly enough, this mainly happens in spring when the vents are opened. Growers will then provide additional CO2 to compensate for the loss. This pollutes the air in the greenhouse, for example with NOx.”
Sander Hogewoning, a researcher at Plant Lighting, adds: “There is a third reason why growers should be taking a critical look at the dose. International research on arable crops indicates that prolonged exposure to higher CO2 levels can lead to ‘lazy’ leaves. When that happens, the key enzyme RuBisCO binds CO2 less effectively. Does this also happen in greenhouse horticulture? That’s precisely what this research was about.”

Airtight cabins

The trials took place at the Westland Demo Nursery (Demokwekerij Westland). They built six 1.4 m2 glass cabins in which CO2, RH and temperature can be precisely controlled. In the first phase, both sweet pepper and tomato plants were studied. The researchers put young plants from a breeder in cabins with 400, 700 and 1,000 ppm CO2. Using a photosynthesis meter, Sander Pot of Plant Dynamics recorded in detail how the leaves use the different concentrations for photosynthesis.
CO2 saturation in tomato plants was found to be 600 to 700 ppm, while in sweet peppers the figure was 700 to 800 ppm. “The step up from 400 to 600 ppm provides far more additional photosynthesis than the step from 600 to 800 ppm,” the researcher says. The amount a grower has to dose for that second step is also much more than for the first step, especially when the vents are open a crack. So the rule “the more, the better” doesn’t hold water. “And yet there can be downsides to high CO2 concentrations. Not all growers take that on board,” Hogewoning explains.

Lazy leaves in sweet pepper

The next important issue the study looked at was whether this high dose would yield “lazy” leaves. The answer? Not in the short term. Leaves that had formed in the breeder’s nursery did not turn lazy. But the same was not true of leaves that had developed entirely in the trial cabins. A CO2 dosage of 1,000 ppm did not produce lazy leaves in tomatoes, but the outcome was different in sweet peppers: photosynthesis was just as high in plants grown at 1,000 ppm and dosed with 900 ppm as it was in plants grown at 400 ppm and dosed at 600 ppm. This is clearly illustrated in Figure 1. In other words, plants that were “pampered” with 1,000 ppm needed a sustained high dose to keep their productivity up.
Hogewoning: “This is caused by the enzyme RuBisCO, which is the key to photosynthesis. The capacity of this enzyme drops. In this case the ‘laziness’ has nothing to do with the stomata, as some growers believe.”

Reactivating quickly

The follow-on research focused exclusively on sweet pepper plants and looked at whether the lazy leaves could be reactivated. “We call that ‘reversible’. We wanted to see whether and how quickly the leaves could get used to a lower CO2 dosage. That is actually what happens in practice. After a winter with a high dosage, the vents are opened a crack in spring. The question is how long the leaves stay less productive then,” Hogewoning explains.
To test that, in 2015 they carried out a trial with sweet pepper plants with doses of 400 and 1,000 ppm. Once the researchers had identified the lazy leaves, they switched two cabins of 1,000 ppm to a varying regime of between 500 and 1,000 ppm, similar to spring in the greenhouse. Using the photosynthesis meter, they determined CO2 uptake in the leaves after six and fourteen days.
Good news for sweet pepper growers: the laziness turned out to be reversible after just six days. Therefore, lower CO2 levels only cause the crop to be less productive for a very short time. “We were quite surprised by that. It means that it isn’t necessary to adjust the dosing strategy in winter. But what is important to remember is that growers who opt for a high concentration need to keep it up right through the winter. The plant gets used to it. And dosing above 800 ppm has very little added value,” Hogewoning concludes.

Eye opener

Whether or not sweet pepper growers can make use of the findings in practice depends on their situation. We ran this past Bart van der Valk of Zwingrow, who grows orange peppers on three sites in the Westland area of the Netherlands. He is positive about the outcome of the research. “We use geothermal heat and we pay quite a lot per square metre for the CO2 we source from OCAP. So we are keen to use it more efficiently.” For him it was an eye opener to discover that the level could be lower in winter.
“We are now dosing 600 to 700 ppm in winter. It’s just as effective as 1,000 ppm. I prefer to keep the CO2 for the spring. What the research also revealed is that lazy leaves can recover again quickly. That’s good to know. Of course, there are still some unanswered questions. For example, I would like to find out what time of day is best for dosing CO2. More research is needed in that area.” But a survey among growers using geothermal heat reveals that there isn’t enough money for practical research yet.


If sweet pepper plants receive a high dose of CO2 over a long period in the winter, they get used to the high level. That produces “lazy” leaves which use the CO2 less efficiently. But this is reversible: when the dose is reduced in spring, the plants adapt within just six days.

Text: Karin van Hoogstraten. Images: Studio G.J. Vlekke.

760 0

The plant can’t function without transpiration. But sometimes it can be somewhat less. Also less than is commonly used commercially. There are plenty of ways to slow down or encourage transpiration which will be discussed in this article.

If you want to read this content you need a subscription, or log in when you already have a subscription.

802 0

The gas carbon dioxide (CO2) is a raw material for photosynthesis. From this, together with water, the plant makes sugars and other compounds. Therefore CO2 is for the plant what food is for man. There is often too little available in the greenhouse air for optimal production. Therefore it makes sense to dose with CO2. The optimum concentration varies over the day and is dependent on many factors.

If you want to read this content you need a subscription, or log in when you already have a subscription.

927 0

The Swiss start-up Climeworks is developing a system that extracts CO2 out of the air for greenhouse horticulture purposes. The system will be tested during a three-year pilot and should be able to capture some 2 to 3 tons of CO2 on a daily basis. This will be piped to a nearby greenhouse to boost the growth of lettuce, cucumbers and tomatoes, according to New Scientist magazine.

The system, called Direct Air Capture (DAC), captures air in closed spaces, such as submarines and space capsules. The captured ambient air is pushed through a fibrous sponge-like filter material that has been impregnated with chemicals derived from ammonia. Once the filter is saturated, the gas will be released by warming it with the heat which is in this case generated by a nearby municipal waste incineration plant. The CO2 thus released is then piped to a 4-hectare greenhouse.

High costs

According to calculations made by the American Physical Society the cost of capturing CO2 on this scale would be 600 dollars a ton, says Climeworks COO Dominique Kronenberg. The Swiss start-up also expects to equal that and eventually get costs down well below that. At that price, taking C02 out of the air is more expensive than removing it from the flue gases of industrial facilities and power plants, where the gas is up to 300 times more concentrated.

Location independent

Despite the high price, Kronenberg notes the many advantages to the DAC process. ‘The advantage of taking it out of the ambient air is that it can be done no matter where you are on the planet. We are not dependent on a source of CO2, so neither will we need to make high costs to transport the CO2 to the greenhouses.’ Climeworks will be using funding from the Swiss Federal Office of Energy to fine-tune the system. The objective of the three-year pilot period is to make the system run more cheaply and efficiently and, in doing so, enable the company to gain a solid foot on the market.

Source: Newscientist.com

700 0

Since 2014 Dutch gerbera grower Reijm Nieuwerkerk has been using a system to actively ventilate the greenhouse air as part of its Next Generation Growing strategy. The continuous refreshment of the air provides an optimal microclimate at the bottom of the crop. The company is producing the same quality gerberas with less energy input.

Reijm Nieuwerkerk cultivates 5 ha of pot plants and 3.5 ha of gerberas at three locations in Nieuwerkerk aan den Ijssel, near Rotterdam, the Netherlands. Annually the company produces 4.5 million pot plants and 16 million gerberas in many colours, from large flowering to minis.
Cultivation is in stone wool substrate in a gutter system. A double screen, comprising a black out and energy cloth, has been installed at the top of the greenhouse. A CHP cogenerator with a flue gas cleaner for CO2 production also generates electricity for the lighting (95 µmol).

Active ventilation

Last year, for the Next Generation Growing, the Active Ventilation System (AVS) by Van Dijk Heating was installed in 7,500 m2 of gerberas. This year the area has been extended by 17,500 m2. The system comprises a wall unit made of plastic which contains a fan, mixing valve, heating element and a filter. From the unit and running along the greenhouse wall is a PVC pipeline which acts as the distribution system. Air hoses that contain small holes for air injection are connected to the pipeline. The air hoses hang under the rows of plants.
The greenhouse is dehumidified thanks to active ventilation of the greenhouse air that is mixed with relatively dry outdoor air. The heating element provides low value heat (40ºC water from CHP) for warming the external air to greenhouse temperature.

Learn from practise

The reason for installing this ventilation system is to produce the same or more gerberas with less energy. “The art is to input the right amount of energy at the right moment. In the past we used to turn on the minimum pipe for this but actually we didn’t know exactly what we were doing,” says Jaré Reijm. He runs the family business together with his brother John. Over the years the grower has carried out several trials with gerberas and therefore has learned a lot about the greenhouse climate without having made too much investment in his nursery. “But then it’s not easy to further improve the greenhouse climate, although also not easy to make an investment and then to earn it back. However, installing this system has worked well. Last year we achieved a good cultivation climate. We were able to keep the climate under the plants somewhat drier and above the plants more uniform,” says the grower.

Better temperature distribution

Joek van der Zeeuw, of Van Dijk Heating, explains: “With traditional methods of growing you always need some gaps in the screen and you have a cold dump were you don’t want it. Now, by using this system to inject outside air into the greenhouse you obtain a small amount of over pressure. That is enough to ensure that no cold air enters through a hole or gap so the temperature distribution in the entire greenhouse is more uniform.”
The grower indicates that the temperature difference used to be 3ºC and now is just 1ºC. Further, he would like to better control the microclimate between the plants. The holes in the hoses where the air comes out are therefore set to point upwards. The air that is injected into the greenhouse has been mixed with air from outside and so contains less moisture. Due to a lower RH the crop is less susceptible to disease. “By continuously refreshing the air, we now have a good climate at the bottom of the crop. As a result we think that the flowers are less susceptible to fungal diseases such as Botrytis. And we can achieve this without using the minimum pipe,” says Reijm.

Drive controlled fans

The system has an air-displacement capacity of 6 m3 per m2. The fans in the wall units are equipped with energy-efficient EC motors that are controlled by a computer network. The fans can be reduced to 50% of the capacity, so they only consume 100 Watts of electrical energy for dehumidification. At full output 800 Watts is needed. Reijm tries to run it for as long as possible at low power, until the valve for the outside air is fully open. If then the humidity in the greenhouse rises, the speed of the fan is increased gradually. In this way the grower makes the most efficient use of the system.
Normally, the ventilation units are fitted in an outside wall to be able to draw in outside air. This was not possible in a partitioning wall with the pot plant greenhouse. Here separate units were made that draw in outside air from the top and have air passage through the roof. This suction hole in the roof is covered with a flat sheet so that the roof cleaner can drive over it.

Winter and summer

“Due to the active ventilation it is possible to use the energy screen more in the winter months because we can better control the climate, the humidity and the temperature distribution,” says the grower. Last summer he used the system for the first time for cooling. This worked well. Cooling was achieved by sucking in outside air and injecting it into the greenhouse.
Reijm: “Despite the tropical temperatures outside the greenhouse remained cool for longer. Even when it was 30ºC outside, it remained 25ºC under the crop. Because we measure everywhere under the crop, we see a difference with the traditionally grown crop. Because the temperature is lower for longer, we can open the vents later. This keeps the CO2 inside. Due to the cooling, the crop remains more active so that the quality of the flowers is better. The diameter and stem length remained the same during the summer. However, this was not the case with the traditional cultivation. The flower was smaller and the stem was shorter.”

Pure CO2

Reijm uses the system for dehumidifying and cooling, but not for heating. The grower doesn’t dare to use the latter for Next Generation Growing. “By heating from underneath we would push the crop too much. As a result the crop would transpire more, which would result in a higher humidify. Then we would have to get rid of the moisture in one way or another and that costs energy.”
A disadvantage of the system is that because less heat is required, the grower has a CO2 shortage. Because the CHP cogenerator produces heat, which the grower would have difficulty getting rid of, it only runs to produce electricity for the lights. However, in the summer months it doesn’t run for long enough to provide sufficient CO2. This summer the grower will have to buy and inject pure CO2.

Uniform growing conditions

The grower would like to have the same growing conditions for all the gerberas. Because they change the crop every three years, they will be able to install this system in the last hectare of gerberas next year. Installing it while a crop is present is not wise, according to Reijm. In addition, they will replace the entire cultivation system so they can do everything at the same time.


Since 2014 Dutch nursery Reijm Nieuwerkerk has been implementing the Next Generation Growing, a system that includes active ventilation. The grower can dehumidify the greenhouse air by mixing it with air from outside. He can produce the same number of gerberas with lower energy consumption. The continual refreshment of the air provides an optimal microclimate at the bottom of the crop. As a result flowers are less prone to fungal diseases such as Botrytis.

Text/photos: Harry Stijger

768 0

Light is more than just the big mechanism behind photosynthesis. Parts of the light spectrum, or simply more or less light, influence the development of plants: germination, flowering, cell division and cell elongation. Light induction also affects the formation of compounds that are useful to humans. It’s a new area with much to discover.

According to researcher Tom Dueck, of Wageningen UR Greenhouse Horticulture, the Netherlands, a plant ‘sees’ its environment via light. It’s not just the fact that light is present but the amount, direction, length (day length) and colour of the light spectrum that play an important role. Plants use light with a wavelength between 400 and 700 nm for photosynthesis. Growers can use UV, blue, red and far-red light to steer the plant. In particular, the ratio of red to far-red determines a number of physiological processes.

Red and far red

Plants absorb light of certain wavelengths via pigments, also known as photoreceptors. There are different types. UVR8 photoreceptors respond to UV-light and are involved in the stress response. Phototropins are involved in the way plants grow towards the light. Cryptochromes ‘notice’ the difference in day length. Phytochromes are sensitive to the ratio between red (circa 660 nm) and far-red (730 nm) light. They cause changes in the hormonal balance and stimulate the production of some compounds.
The researcher focuses mostly on the phytochromes. How these work exactly is complicated. According to Dueck the ratio of red to far red light affects the three dimensional shape and function of the pigments. This ratio is also called the ‘phytochrome stationary state’ (PSS). At a higher PSS there is more red light in the ratio than at a lower PSS. A higher PSS leads to, for example, cell elongation and it influences the flowering processes. A low PSS affects germination and sensitivity to day length.
The ratio red:far-red is very subtle. In the summer, sunlight with 0.7 has a low PSS (red:far-red ratio). The PSS of red LEDs, without sunlight, is 0.87. This is high, but the difference in ratio is just 0.17.

Flower bud induction of phalaenopsis

Dueck gives a few examples of steering plant processes. Normally phalaenopsis plants have to remain cool at 19ºC for six to nine weeks. The cooling breaks bud dormancy, stimulates growth of the stems and causes flower bud induction. According to Dueck a whole mechanism of plant hormones are behind this and are active during the various stages of development.
The cooling period activates phytochrome B. This phytochrome stimulates the production of cytokinin, inhibits auxin production and stimulates the formation of gibberellin. Cytokinin breaks the bud dormancy and stimulates bud development and branching. Auxin works against apical dominance and ensures that several stems develop at the same time. Gibberellin stimulates flower bud development.
The question is does lighting also work in this way on phalaenopsis. It appears likely, but if the light spectrum influences the hormone balance in the same way as cooling is not clear. During the research Dueck considered if flower bud production is also possible during this period by giving the plants on two occasions four weeks of light of a high PSS via artificial lighting with SON-T lamps that contain a relatively high amount of red. The aim is to activate the phytochrome B.
“A lot of red light, especially in the second phase of the induction, appears to do approximately the same as the cooling. Red induction light can partly replace cooling. We want to start a follow-up project to research this further,” says the researcher.

Chrysanthemum cuttings

A second example mentioned by Dueck is the research into the effects of far red light on the development of chrysanthemum cuttings. The cuttings arrive from Africa and rooting takes seven to ten days before the grower pots them on. During the trial, cuttings from the cultivars ‘Baltica’ and ‘Feeling Green Dark’ received different colours via LED-lighting: 40 µm red (660 nm); 40 µm red plus 8 µm far red (730 nm); 40 µm blue (450 nm) and 30 µm red plus10 µm blue and 8 µm far red.
“The roots increase in number and become longer with more far red light. This shows that with just a little light you can steer the plant so that it can be planted earlier. This is a gain for the grower.”

Effect on compounds

Induction light influences the formation of different secondary metabolites, which can be used for numerous applications, such as artificial colourings, medicine and cosmetics or in the food industry. Dueck gives a few examples.
Since 2010 colleague Silke Hemming has been working on the production of high quality ingredients from algae grown in Dutch greenhouses at Wageningen UR, Bleiswijk. Part of this involves stimulating the production of the red colouring astaxanthin in the algae, Haematococcus pluvialis, by using induction light. This red algae can be used as a food ingredient during salmon and shrimp production to influence their colour.

Greenhouse as pharmacy

A new projects aims to stimulate the production of the dark indigo colour by the ordinary plant, Polygonum (knotweed). Dueck: “We want to stimulate production through a combination of red induction light, more light, a longer day and more CO2.”
Research has also been carried out into the possibilites of stimulating plants to produce the protective substances anthocyanins. These could help plants to be more resistant to high radiation when they are grown in space. Light induction can stimulate the production of these protective anthocyanins.
Dueck sees good opportunities for using light induction to stimulate the production of expensive ingredients. In this respect Wageningen UR is running the project Kas als Apotheek (Greenhouse as Pharmacy). Its a new path along which there is much to discover.


It is possible to use light to steer certain plant processes or to encourage the production of substances. The ratio of red to far red light appears to influence plant physiological processes such as elongation, flowering and germination. Practical examples are the use of induction light to replace chilling of phalaenopsis to encourage bud formation and increasing the amount of far red light during the rooting of chrysanthemum cuttings for more and longer roots. By using induction light it is also possible to stimulate the production of certain substances, such as colourings, protective substances and products that can be used in medicines or cosmetics.

Text/photos: Marleen Arkesteijn