Grow Guides · January 12, 2025
Greenhouse Build Week 2: Covering and Ventilation
From frame to functional growing space
The Critical Hours
Week two arrived with a 20-knot wind forecast. We had to get the plastic on before Friday or risk an expensive tarp-less weekend. It became a race against weather and sunset.
Plastic Selection and Installation
We chose 6-mil greenhouse plastic--thick enough to insulate but still flexible enough to work with. The key was starting at the peak and working down, anchoring with wooden battens as we went.
By Tuesday afternoon, we had walls. By Wednesday, a roof. The interior temperature was already 15 degrees warmer than outside, and we hadn't even installed ventilation yet.
Cooling System: Fans and Louvers
Utah summers are hot. A sealed greenhouse becomes an oven. We installed two large exhaust fans and solar-powered roof louvers. On a 95-degree day outside, we can keep the greenhouse at 85 degrees inside.
Proper ventilation is as important as the greenhouse itself. Temperature swings and high humidity invite disease. Plan your cooling before you close up the structure.
Utah State University Extension Climate Control Guide — Dr. Heidi Kratsch (2024)
Benches, Watering, and First Plantings
Benching Strategy
We built three raised benches down the center, leaving walkways on both sides. Metal benches heat up; wood benches rot. We settled on treated lumber with a gravel base for drainage.
Water Supply
Hand-watering a greenhouse is romantic and exhausting. We ran drip lines off the main garden system, installing a timer. Now we set it and forget it (mostly).
By Friday evening, the greenhouse was functional. We planted our first tomato seedlings Saturday morning. By July, we'd harvested three times more tomatoes than our outdoor beds.
A greenhouse isn't just a building. It's a climate you control. And control is everything in farming.
Want to learn how to modify an existing greenhouse? We've been there too.