Hoogenboom Alstroemeria in Nieuwe Wetering in the Netherlands expanded its grow light system last year. In one section of the greenhouse they have installed LED lights in between the rows of controllable SON-T lights, ramping up the light output there by 50% to 150 μmol/m2/s. “You don’t always need the radiated heat that SON-T lights produce. We can light our crops more intensively and more flexibly with this hybrid system,” partner Dick Hoogenboom explains. “It produces visible results.”
Brothers André and Dick Hoogenboom have been growing alstroemeria in their 2.9 hectare greenhouse in Nieuwe Wetering since 1985. Their aim is to produce the most beautiful, strongest and healthiest cut flowers. “It takes a long time to establish a good reputation, but once you have it, you can lose it again very quickly,” grower Dick says. “We have to work hard to stay ahead of the field because the competition never stands still.”
Grow light plays a key role in the battle for quality. The brothers installed their first lighting system in the late 1990s, with 600 W SON-T lights producing 4000 lux or 50 μmol/m2/s of PAR light.
“We increased the output every time we replaced or renovated something,” the grower explains. “We have had around 100 μmol for eight years now. Five years ago we upgraded our entire power system and we replaced the 600 W bulbs with 1000 W ones, which we can either have running on full or half power.”
SON-T or LED
The growers wanted to up their lighting capacity yet again last year. First they had to decide whether to go for extra SON-T lights or install a second, LED-based system.
Hoogenboom: “The easiest and cheapest option would have been to put in extra SON-T lights. But we didn’t need even more radiated heat so we opted for the more expensive LED system. We deliberately went for Phillips lights; they weren’t the cheapest but we have the most confidence in the quality, reliability and after-sales service you get from this supplier.”
LED lights don’t radiate heat onto the crop and can be used whenever additional grow light is needed. Hoogenboom aims for a day length of 16 hours. Between 1 August and 1 April the daylight is always extended with artificial light (and radiated heat) from the SON-T system. At the beginning and end of this period the days are usually long and light enough for them to manage with a light intensity of 50 μmol.
“We switch the lights on full power on around 1 October,” the grower adds. “Now that we also have LEDs in the greenhouse, I can decide which system to switch on first. If the temperature is still warm enough, we will use the LED system. I have often used the LED lights at times when the lighting in the section that only has SON-T was left switched off because it would otherwise have got too hot there. You can get rid of excess heat by opening the vents, of course, but that costs you CO2 as well, which impacts on growth.”
During the winter and on chilly spring days, the grower switches the SON-T system on first because the radiated heat is very useful. At that time of year the LEDs are added in to ramp up the light level to 150 μmol when necessary.
Noticeably higher yields
The grower is convinced that there is scope to get even more out of his hybrid lighting system by working with crop adviser Marco de Groot and tweaking the climate. Although the new LED system has only been in use since November last year and at the time of writing he has yet to experience using it between 1 August and 1 November, he is happy with the results so far.
“Under the higher light level we used from 1 November onwards, the crop has been producing noticeably thicker, firmer and stronger stems,” Hoogenboom says. “What’s more, yields are quite a lot higher. Depending on the variety, by 1 April we were cutting between 30 and 50 stems more per square metre than usual.”
Hoogenboom also noticed less bud dehydration and deformation in the greenhouse with the higher light levels. On the other hand, he has noticed that more light means more watering. “The crop is more active so it transpires more. I didn’t really take that on board to begin with. But there was a leaking tap in one bay so it was wetter there than in the other irrigation sections for some time, and in the spring we noticed that that crop was fuller and was producing more flower spikes. So I’m convinced there is even more room for improvement. That makes us even more confident of a positive return on our investment.”
Alstroemeria can get off to a good start with higher light levels than are generally used at present. SON-T lights also emit radiated heat and meet the plant’s basic needs. If you don’t need extra heat at the top of the plant, LED lighting can boost light levels in the winter months, which translates into more and stronger flower spikes and less bud dehydration and deformation.
“You still need to do the maths”
Crop adviser Marco de Groot is keeping a close eye on the developments with grow light in alstroemeria. He helped the Hoogenboom brothers do the maths to underpin their investment decisions.
“Lighting levels in many ornamental crops continue to rise,” he says. “Alstroemeria is no exception. And that has to happen if our growers are to compete with Africa, where alstroemeria cultivation is expanding rapidly. More light is good for the quality of the crop, yields and more regular workforce deployment between October and June. But you do need to take a critical look at where you’re coming from, where you want to go and the best way to get there.”
The adviser continues: “For growers currently working with low light levels, a heavier-duty SON-T system would be the best choice. If you are already using slightly more light and don’t need extra heat, you should rather opt for LED. Don’t forget that unlike rose and gerbera, photosynthesis in alstroemeria has a response time of around 30 minutes. LED light doesn’t increase the leaf temperature, unlike SON-T light. If the leaf temperature is too low, that can delay the response time even more. Extra LED light is only effective when the basic level is covered by SON-T light.”
In addition, the light response varies from variety to variety because of the strong genetic variations. Virginia can use extra light efficiently whereas other varieties often respond more slowly. “It’s important to take these aspects into account,” De Groot concludes.
More growers gaining experience
According to plant specialist Stefan Hendriks of Philips, a good number of ornamental growers are gaining experience with hybrid lighting or 100% LED. “We are seeing a growing trend towards LED in the market as growers become more and more aware of the advantages. But it is important to bear in mind that it’s not simply a question of installing LEDs and carrying on as usual. You also have to control the climate differently. LED lighting provides you with an extra tool because you can control heat and light separately, which you can’t do with SON-T.” In addition to research in vegetable crops, Phillips is also working with ornamental crops such as rose, gerbera, alstroemeria, chrysanthemum and phalaenopsis.
More and more growers are realising that LEDs deliver benefits for the crop, quite apart from the fact that you can’t always increase light levels with SON-T in some crops because of the excess heat they produce, Hendriks says. In practice, you can get more lighting hours out of LED than with the same crop under SON-T. “This boosts yields and quality. The use of LED is growing, and with increasing success. This trend looks set to continue and we expect that LED systems will most likely take over from SON-T completely in the longer term.”
Text and images: Jan van Staalduinen.