The Neglected Input
September 1, 2009 How many times have you stared through your greenhouse roof, remarked on how remarkably cloudy it is and done nothing to alter the light your crop is receiving? Hopefully, your answer is no more than a few times, but odds are lighting is an overlooked input at your operation unless you’re using supplemental lights and you have a good understanding of how you can use light most effectively.
Let’s face it, you’re busy. Your head grower has his or her hands full, too, and you’re probably thinking you don’t have enough time, money or resources to devote toward having the most efficient lighting possible. There are, however, simple measures growers can take to enhance lighting, and a little understanding of lighting can save you time, money and resources in other areas.
“Sometimes, light is ignored and it really shouldn’t be,” says Johann Buck, a horticulture specialist for Spectrum Technologies. “It drives photosynthesis, which is driving some of the other physiological processes within the plant. Some of the best advice I ever received was: To be a successful grower, you’ve got to think like a plant. That’s the bottom line.”
A lighting discussion may seem like a return to basics, but we have much more knowledge about lighting today thanks to plant physiologists who understand the value of daily light integral (DLI) and other measurements that make a difference in the greenhouse. Plant pathology studies have subsequently resulted in the development of effective light measuring tools. And the growers progressively using those tools are the ones who are able to make decisions on the crops they should be growing and the structures in which they should be growing.
Those progressive growers are also the ones who understand how supplemental lighting can best be employed.
“We’re really trying to get growers to realize light is a significant factor, something that shouldn’t be taken for granted,” says Mike Thurow, founder of Spectrum Technologies. “Now, we have tools to measure light. We can see how different light is when we pull shade cloths, and we can see what kind of different greenhouse structure coverings affect transmission of light most.”
Consider Daylength
Bruce Gibson, general manager at Northwest Horticulture, knows all too well about poor natural lighting. Gibson jokes that Northwest Horticulture, located in Mt. Vernon, Wash., is famous for its cloudy days, and the operation doesn’t have the luxury of much light.
Fortunately for Gibson, Northwest Horticulture is primarily a perennials grower. An annuals or poinsettia grower in the Northwest, however, faces serious lighting challenges and subsequent pressures to produce early spring crops.
“One thing you can do is buy some larger light inputs to create a high-light area,” Gibson says. “You have to look at what kind of environment you’ve got. If you’re looking for early geraniums, it might be best to instead buy something that’s been propagated in the sun for six to eight weeks.
An unpredictable buying cycle doesn’t make lighting preparations easy, though.
“You just have to look at your operation and ask, ‘Should I buy a smaller [light] input and have a longer crop time or buy larger inputs and have a shorter crop time,” Gibson says.
Either way, you’re bound to need more lighting the farther north your greenhouse operation is. And don’t think you’re immune from needing lights because your operation sits in a warm-weather state like California, Florida or Texas. You may get more intense daylight than growers in Michigan, Ohio or Pennsylvania, but your daylight length is the same as growers in those states during those short winter days.
“In the South, growers always say they have plenty of light,” says Peter Berkhout, managing director of Kavita Canada. “They probably have better daylight than those in the North, but the best reason to use lights is for daytime extension.
“In the summer, everything grows fine because we have 16 or 17 hours of daylight. But in the wintertime, you are lucky if you get eight hours. Then, you have those cloudy days on top of that.”
Another factor to consider, Spectrum’s Buck says, is greenhouse lighting varies tremendously from place to place within each facility.
“Light can be vastly different from spot to spot, and it all depends on the type of shade and the position of the sun throughout the day throughout the year,” Buck says. “When you look in, you have structural shading. And that’s a component of greenhouse design. Light is also a factor if you’re growing hanging baskets.”
But the growers who know what they’re doing with hanging baskets use them to their advantage, Buck adds.
“If growers have a low-light crop but a high-light condition, and they’re growing a hanging basket that requires high light, they can use that as their shade,” he says.
There are, in fact, all sorts of tricks growers can use to enhance lighting. And the first step toward improved lighting is the realization that the knowledge and tools exist to create the optimal growing environment for your crops.
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