Gardentalk – Keeping the heat down and the air moving in your greenhouse

Hot greenhouse
Air inside this North Douglas greenhouse made from upcycled double-paned windows already has exceeded 120 degrees and 70 percent humidity before noon in late May 2020. (Photo by Matt Miller/KTOO)

It is certainly possible for your greenhouse to start overheating, even in Southeast Alaska’s usually cool and damp climate. Not only will some plants and vegetables be unable to tolerate such extremely hot conditions, it would also be uncomfortable for a gardener to work inside.

Master Gardener Ed Buyarski recommends keeping greenhouse air from exceeding 100 degrees. That can be done by using fans and opening doors, windows, and vents to pull in cool air and push out hot air.

“They actually talk about moving a greenhouse full of air every minute or every two minutes,” Buyarski said.

He suggests checking out free publications on greenhouse design and operation produced by the University of Alaska Fairbanks’ Cooperative Extension Service.

High humidity, along with poor air circulation, can kick off rapid fungus growth.

Instead of spraying water on plants in the greenhouse, Buyarski advises using a drip watering system or soaker hoses in planters.

Don’t space your plants too close together. Otherwise, air cannot flow through them.

And, covering planter soil with plastic mulch will keep most of the moisture in the soil and prevent it from quickly evaporating into the greenhouse air.

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