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Greenhouse From Spring to Summer Greenhouse From Spring to Summer

Climate (meteo)

Transitioning Your greenhouse from spring to summer

As spring turns into summer, greenhouse growers across the country are starting to prepare for longer, warmer, and more humid days. They are starting to adjust their climates and reboot systems that have been sitting idle for months. This transition into the more extreme weather of summer can be both a real challenge and a great opportunity for many growers.
w Shade curtains
Shade cloths, which can help reduce incoming light, come in various levels of light intensity control and photoperiod control.

In this article, we will discuss three of the major changes that summer brings to greenhouses (more light, higher temperatures, and higher humidity) and what growers can do to abate any negative impacts and maintain a stable greenhouse climate. We will also share some tips on how to maximize productivity of your greenhouse in the summer months.

Light Intensity/Photoperiod (DLI)

The onset of summer generates a lighting change for greenhouse growers, specifically longer photoperiods (a.k.a. daylengths) and increased light intensity, both of which add to daily light integral (DLI). Faster crop growth rates occur under high DLI; however, increased plant stress is of concern. For example, head lettuce grows optimally under a DLI of 17 mol·m-2·s-1, but when the optimal DLI is exceeded, the plants can grow too fast, resulting in tipburn (a physiological disorder that causes calcium deficiency and marginal necrosis/distortion of young leaves).

Additionally, every plant has a threshold of light intensity that correlates to optimal photosynthetic gain, and beyond this threshold, increasing light has either no effect or negative effects on photosynthesis. Thus, in the summer months it is crucial to both have accurate measurements of light in the greenhouse at all times and to understand the tools at your disposal to control the amount of light reaching your crop, so as to avoid the potential negative effects of too much light.

As a greenhouse grower, you have a handful of tools in your kit to reduce incoming light. Shade cloths are among the most common throughout the industry. They come in various levels of transmissivity (intensity control), as well as opaqueness (photoperiod control). If your shade cloth is motorized, make sure your motors are working before the summer starts.

In addition to shade cloths, latex shade paint is another common mitigation tool to reduce incoming light. It can be sprayed on at the beginning of summer and washed off at the end. If manually applied, be sure to check your forecast outlook, as timing will save you money. Applying too early or too thickly will reduce the amount of available light, thus slowing down crop growth. Accurate light measurements and an understanding of your crop’s biology will tell you when to employ shade. An effective shade strategy in the summer months is crucial to keeping your crop healthy, strong, and stress-free.

w Tipburn on head lettuce
Excess light levels in lettuce can lead to tipburn, a physiological disorder that causes calcium deficiency and marginal necrosis/distortion of young leaves

Also, as light increases, so does the plant’s water consumption. Be prepared to adjust your irrigation cycles. You may also need to adjust your fertilizer recipe. The ratio of water to nutrients that the plant takes up increases as light increases, so you may need to decrease your nutrient solution EC (electrical conductivity) to maintain a stable root-zone EC.


Increases in light intensity and photoperiod have a direct connection to the temperature in your greenhouse. Similar to increased light, increased temperature can have positive effects on plant growth (speeding up development rate), but also a few negatives as well. High temperatures correlate with reduced seed germination for many crops, premature bolting in lettuce, reduced flower development in strawberries, and reduced fruit set in strawberries, peppers, and tomatoes. Furthermore, many insect pests have a quicker reproduction time in warmer temperatures, requiring more frequent integrated pest management (IPM) applications.

If not properly managed, summer heat will cost your greenhouse money. Before the summer comes, be certain that your cooling systems are in place and operational. Passive and active venting that has been insulated for winter should be free of obstructions. Exhaust fans will be run for longer hours and should be inspected for proper alignment, functionality, and lubricated if necessary.

Evaporative coolers and positive pressure (swamp) coolers should be inspected for leaks. If not drained properly in the fall, pipes may have frozen and cracked. If you use a fog cooling system, nozzles need to be inspected and cleaned of obstructions to assure that when the heat comes, you’re ready. Keeping your greenhouse to an appropriate range of temperatures in the summer months is absolutely necessary for healthy crop growth and for the health and safety of your greenhouse employees.

Relative Humidity

The increased light in the summer months brings not only warmer temperatures but also increased humidity. While most growers already monitor relative humidity, this only accounts for the water vapor that is currently in the air and not how much it can hold. Since the saturation target of water in air varies as a function of temperature, relative humidity is not the best predictor of plant transpiration and water loss. Vapor pressure deficit (VPD), on the other hand, is the difference between the amount of moisture in the air and how much it can hold at saturation.

This makes VPD a more useful predictor in the greenhouse. Hot summer temperatures may feel humid, but warmer air has a greater capacity to hold water before condensing onto leaf surfaces stalling transpiration. Substrate moisture levels, therefore, need to be closely monitored to avoid water stress. If your irrigation schedule is on a timer, it may need to be readjusted for the changing season.

To help mitigate high relative humidity (low VPD), look to reduce any extraneous water introduced to the greenhouse. Evaporation of water from greenhouse floors, holding tanks, root substrates, and other surfaces, as well as transpiration, all add to the humidity in the greenhouse. At high relative humidity (low VPD), pathogens such as botrytis (gray mold) and powdery mildew are favored. Moreover, various physiological abnormalities like tipburn in lettuce and blossom end rot in tomatoes are at risk in humid environments.

Use of horizontal or vertical airflow fans improves microclimate humidity/VPD and decreases sensitivity to physiological disorders or disease. Additionally, continuous or frequent air exchanges in the greenhouse may be required to relieve high relative humidity through passive or active venting. Also, if misting systems are employed for cooling, be sure they are running only when plants have ample time to dry out before nightfall when outdoor ambient humidity increases.

While these summer weather changes bring forth many challenges to overcome, they also can create many opportunities for increased production and revenue. Warmer temperatures in the greenhouse can allow you to grow heat-loving crops like basil that you may not be able to grow at other times. Longer days and more light can greatly reduce growth cycles for many crops, which will allow you to harvest and sell more product faster. The warmer weather also drives people outside, which leads to an increased demand for bedding and landscaping plants. Additionally, restaurants, produce shelves at grocery stores, and farmers markets all see increased activity in the summer, which creates a higher demand for fresh produce.

It is imperative that growers prepare their greenhouse for the upcoming summer months, not only to abate the negative effects of extreme weather conditions, but also to prepare for the changes in production and sales, so as not to miss out on any revenue.


Climate (meteo)

Casey Houweling have a hard time with extreme heat Canada

The extreme heat wave in the Canadian province of British Columbia continues. Although plants can survive temperatures above 30 degrees Celsius, it is not easy for growers and their plants. “The high temperature for 24 hours makes it so difficult,” says Casey Houweling of Houweling Tomatoes.

It’s been nearly 10 years since the company was named Houweling’s Group instead of Houweling’s Hot House, but right now Casey Houweling’s Delta, British Columbia greenhouse is definitely feeling very “hot” again. The province is suffering from an extreme heat wave: daytime peaks can reach 33-43 degrees, temperature records are being broken. “We’ve seen the temperature in the greenhouse rise above 34 degrees. If that’s one or two days we can handle that, but it’s the 24-hour temperature that really makes it difficult for us,” Casey says. At night the temperature drops to 18 – 21 degrees Celsius, which is very high for the region. 


“The effect of the weather depends on the crop phase,” Casey continues. “The tomatoes will make it, but we have also transplanted some cucumbers. They have just come out of propagation and are now really having a hard time.”

Whitewashed roofs
With companies in Camarillo (California), Mona (Utah) and Delta (British Columbia), Houwelings’ team is used to growing in different climate conditions. With a timely warning about the extremely hot weather, Casey is confident that growers have provided whitewashed roofs to reduce the temperature. “In this area we are used to a high light intensity: we are more south than in the Netherlands, for example, and easily reach 1000W. Growers of sensitive crops such as sweet peppers lime their greenhouses to limit the amount of sunlight and radiant heat. Tomato growers usually do that. not, but with this weather you definitely want it.”

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Casey Houweling have a hard time with extreme heat Canada 104

Temperatures are likely to drop again later this week. “If the wind turns and comes back from the ocean, we’ll go back to 23-24 degrees or less,” Casey says. “Usually it is cool 2 to 3 days earlier here than in the Upper Fraser Valley, where there are more greenhouses. We’ll see, in 2 or 3 days.”

Incidentally, a record temperature of 49.5 degrees Celsius was recorded yesterday . So sweat a lot. 


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Technique system

Getting your deck cleaner through the winter without any damage

Getting through the winter without any damage

With more than 30 years of experience and almost 1000 installations worldwide, they know how and what to do at Besseling Techniek. The machines are used year-round, to clean for more light output or to coat for additional protection. Machines always need their maintenance, but with a cold winter on the way, the deck cleaner builder wants to pay a little extra attention to winter preparations.

 Circled The most important part of the Roofmaster deck cleaner that needs to be drained.  

Getting through the winter without any damage
The forecasts for next week in the Netherlands are unanimous: there is a cold front approaching and that means that the roof washers need to get through the winter without any damage. The law of nature is clear: water freezes at temperatures below zero. And ignoring this law is asking for trouble.

With several tips and short actions, you can avoid damage to the machine, and therefore extra costs. These are included in the Roofmaster user manual, but also below, to remind you.

First of all, safety first. The ladder can be slippery, so take sufficient precautions (good shoes, personal protective equipment) before you go on the platform.

Action: Drain!
That means removing water from metal and plastic parts.

  • Open the 4 taps at the bottom of the machine’s main brushes. This will prevent the brush frame from freezing and breaking. Opening the taps is not always enough because they can be clogged. Therefore, check if any water comes out and puncture if necessary.
  • Some older models have a water filter on top of the platform that is fitted with a drain trap. Don’t forget this.
  • With most Roofmaster models, the pump is frost-free inside the greenhouse. When the pump is mounted on the platform’s lower beam, it can be easily reached and drained. Just to be safe, these can be disconnected and kept indoors. When the pump is on the platform, this is a little more difficult, which is why people choose to only drain it.
  • If there is also a shading kit mounted, for spraying coatings and cleaning agents, you can easily disassemble this set and store it indoors.
  • If there is a Dosatron on the machine, we recommend that you also disassemble it and store it indoors.
  • Furthermore, it is not an unnecessary luxury to check the pressure regulators.

When the frost comes and the machine is well prepared for winter, the grower can put his skates on and not worry about anything. Time for “koek-en-zopie”! (a Dutch term for the food and drinks sold during ice skating).

For questions, growers can always call the Besseling experts, who can be reached at: + 31 (0) 72 5719712

For more information:besseling
Besseling Techniek  


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