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.”

“Congress, you have orders from the president. Extend the implementation period of the hemp ban.”

By Adam Terry, Cantrip

As it was widely reported, last week the entire cannabis universe watched as President Donald Trump signed an executive order to change marijuana from schedule I to III. What wasn’t as widely reported was what Trump also did: He addressed lawmakers again on the law As Congress passed the new definition of hemp last month.

The exact text of the executive order reads:

“The Assistant to the President and Deputy Chief of Staff for Legislative, Policy, and Public Affairs will work with Congress to update the final statutory definition of hemp-derived cannabinoid products to ensure that Americans have access to appropriate full-spectrum CBD products, in line with Congress’ intent to reduce the sale of products that pose serious health risks…”

This provision is careful and detailed. He directs a deputy chief of staff to work with Congress to update the new definition of hemp, directly acknowledging what the hemp industry has been saying for weeks: full-spectrum CBD products are not eligible under this new language.

He specifically acknowledges that if CBD products are to be subsidized or covered by Medicare, as is part of Trump’s plan, those products will be hemp-derived.

Full-spectrum CBD is a staple for many Americans. It is a lifesaver for veterans and senior citizens who rely on these products for various therapeutic purposes. It is a crucial element for some people with epilepsy, including pediatric patients. I’ve had moms and dads message me that Epidiolex, a federally approved CBD prescription drug, wasn’t working for their kids, and instead they were relying on other CBD products to find relief for their kids.

This is not just politics for them, but a stark reality.

You can’t have full-spectrum CBD with only 0.4 mg of THC per container, as required by the newly enacted change to the federal definition of hemp, and the president acknowledged that in his executive order, I’m sure with counsel to groups like the Commonwealth Project who were at the signing. Therefore, it is very likely that the definition of hemp will be reopened and legalized.

So here’s the bottom line: this conversation will take time, and probably longer than hemp has left before the ban comes into force late next year. While I have been working with the New Jersey legislature for nearly three years to craft a bill to regulate hemp cannabinoids in a way that does not diminish the CBD market, it has yet to make full impact in the state due to this complexity.

This means that the best first step for Congress to take is to extend the deadline for implementing a revised definition of hemp to ensure access to full-spectrum CBD for the tens of millions of Americans who will lose access next November if this language is enacted.

With 2026 being a close election year, most legislation will slow down after April, so it is unlikely that a final bill updating this language and regulating hemp cannabinoids will reach the finish line until the next Congress, which begins in January 2027. And the extension must pass soon, because farmers can’t plant in the spring if their harvest is in time.

I look forward to the next interview. Hemp needs to be regulated in this country, that much is clear. The White House has just sent a signal that prohibitionist redefinition cannot stand if the people who rely most on cannabis are to do well, especially in red states that voted for this president and those who have no access to cannabis outside of hemp products.

Congress, you have orders from the president. Extend the implementation period of the hemp ban, and let’s do the real hard work to craft legislation that includes safe access to cannabis for Americans in this great nation.

Adam Terry is the co-founder and CEO of THC-infused beverage company Cantrip.