Night hours present a persistent and costly challenge for commercial greenhouse operators. When the thermal screens are closed and the ventilations are closed, the greenhouse is closed, trapping the moisture produced by the crop. This creates a high-stakes battle against condensation, disease and unnecessary energy loss. Amir Kandlik, B.Sc. Plant Science and Genetics in Agriculture and agronomist with Drygair explores the critical problem of nighttime humidity and explains the strategic shift from traditional ventilation-based control to a system built around active indoor dehumidification. “This ‘closed greenhouse’ approach improves energy efficiency and supports stronger crop health.”

© Drygair

Night challenge: Thermodynamic and pathological risk
“At night, plants continue to transpire even though photosynthesis has stopped. Without the drying effect of daytime conditions, the air mass in the greenhouse quickly approaches saturation,” says Amir. “Traditional methods rely on ventilation, but ventilation replaces warm, CO₂-rich air with cold outside air. This increases heating demand, destabilizes temperatures and can introduce more moisture, especially in humid weather.”

A variation of this, heating the air before it is vented, wastes energy because the air conditioner is blown out immediately. “In cold, rainy, or snowy conditions, ventilation becomes impossible and humidity increases unchecked. As relative humidity rises above 85 percent and temperatures drop, surface temperatures can drop below the dew point. Condensation then forms on leaves, fruit, and structural elements, creating conditions that promote Botrytis, powdery mildew, and powdery mildew.”

Solution: “Closed” paradigm with active dehumidification.
A more advanced strategy replaces night ventilation with active internal dehumidification, keeping the greenhouse closed. Amir explains that it starts when the unit pulls in moist air, cools it below its dew point and condenses the water vapor into liquid form. “The latent heat released by condensation is captured and recycled, heating the dry air before redistributing it throughout the cottage. Instead of losing heat to dryness, this method converts moisture into heat and creates a net positive energy cycle.”

© Drygair

Basic advantages of the closed night strategy
This approach improves disease prevention by maintaining a stable vapor pressure deficit and preventing dew formation. Keeping surfaces above the dew point significantly reduces disease pressure. Flower tests recorded a 98% reduction in Botrytis when relative humidity remained below 85%. Energy efficiency is also increased because the airfields remain closed and latent heat is recovered during dehumidification. Vegetable producers have reported energy savings of 50%.

“Climate uniformity is improved as constant air circulation removes microclimates, and sealed conditions store CO₂ for uptake at dawn,” says Amir. Crop quality and yield benefit from consistent transpiration and improved movement of nutrients and calcium. Basil had a 15 percent yield increase without downy mildew, and unheated tomato houses had a 25 percent higher yield per stem.

Practical settings for leaders
Adopting this strategy requires changing the operational logic, which is usually handled by a climate computer. “During the day, the vents are open and the natural ventilation manages the humidity, so the dehumidifiers are turned off. At night, when the outside temperature drops below the indoor set point, the vents and screens close, and the dehumidifier operates at an RH of about 75 to 80 percent. The priority is to maintain a dew point range of at least 2 degrees. While heating is used only for temperature stability, nighttime temperatures stay below 10 degrees Celsius. in regions with , an additional defrost coil is required for continuous operation.

Looking at the field results
Field studies show that flowers grown according to this strategy maintained lower relative humidity, achieved significant energy savings and did not require night ventilation. Basil trials showed a 15 percent increase in yield and zero downy mildew. Tomatoes and peppers have seen a 5 to 25 percent increase in yield and a 98 percent reduction in disease. Cannabis growers recorded 30 to 40 percent higher yields with about 50 percent energy savings.

Specific questions about geography and climate
In very cold climates, this view is especially good. Ventilating at minus 10 degrees Celsius creates an extreme heating load, and sealing the greenhouse and dehumidifying the interior retains heat, recovers latent heat and reduces boiler use. In hot and humid climates, night ventilation is unreliable during warm or rainy weather. Active dehumidification removes moisture in a controlled manner, and with additional Air-Water Heat Exchange, the system can heat or cool the air through an external water loop.

Supporting scientific and technical references
Research includes Elad and Shtienberg’s work on Botrytis cinerea, University of Massachusetts Extension greenhouse moisture reduction guidance, Stanghellini’s transpiration studies, and Ho and Adams’ work on water and nutrient uptake in tomatoes.

Without ventilation
“Nighttime humidity is not a problem to be banished, but an imbalance to be managed,” says Amir. “The closed greenhouse strategy treats moisture as an energy resource instead of a waste product. By keeping greenhouses closed at night and using active internal dehumidification, growers can reduce disease, improve energy efficiency, retain CO₂, stabilize the nighttime climate, and increase yield and crop quality. This is one of the most impactful changes in modern greenhouse climate management.”

A bipartisan majority of Americans support federally regulating marijuana, according to a new poll. And most believe it should be perfectly legal for adults to use cannabis.

The YouGov poll was released just days after President Donald Trump addressed the attorney general quickly complete the process of moving marijuana from Schedule I to III of the Controlled Substances Act (CSA).

The reform would not legalize cannabis, but would symbolically recognize the plant’s medical value, while allowing marijuana companies to take federal tax breaks and remove some barriers to research related to Schedule I drugs.

According to the poll, Americans agree with the policy change. Here’s how the question was posed:

“Do you support the government’s reclassification of marijuana from the most restrictive drug category to a less restrictive category that allows for research into its potential medicinal uses?”

Overall, 70 percent of respondents said they “strongly” (42%) or “somewhat” (28%) approve of rescheduling. Only 16 percent said they were against the reform, and 14 percent were not sure.

Notably, support crossed party lines, with 78% of Democrats, 69% of independents, and 66% of Republicans supporting cannabis reclassification. Majority support is consistent with previous polls, among others a survey released earlier this year by a company with ties to the president.

YouGov also asked about the possible legalization of adult marijuana possession, and a small majority (54 percent) said it should be allowed, including 68 percent of Democrats and 55 percent of independents. Republicans were evenly split on the question, with 41% in favor and 41% opposed.

Additionally, a majority of respondents (76%) also said that marijuana “definitely” (43%) or “probably” (33%) has “legitimate medical uses.” There was also a bilateral agreement on that question. Most Democrats said cannabis has medical value (84%), followed by independents (74%) and Republicans (73%).

The survey 31,080 US adults were interviewed between December 19 and 22, with a margin of error of +/- 0.8 points.

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It’s Marijuana Time tracking hundreds of cannabis, psychedelic and drug policy bills in state legislatures and Congress this year. Patreon supporters by pledging at least $25/month, you’ll get access to our interactive maps, charts, and audio calendars so you never miss a development.

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The reorganization process started by the Biden administration, which Trump has now called for an end, is still pending. But as previous surveys have indicated – and this latest survey has reinforced – it is a political reform of the whole corridor.

The president said last week that cannabis can “make people feel a lot better.” It serves as a “substitute for addictive and potentially deadly opioid painkillers.” He clarified, however, that he personally has no interest in using marijuana himself.

So does Trump He dismissed the concerns of GOP lawmakers who oppose the reconsiderationstating that an overwhelming majority of Americans support reform and that cannabis can help people with serious health problems—including his personal friends.

user photo Brian Shamblen.