Last year I built a small greenhouse using 2×2 lumber and plastic sheeting. I wanted a controlled environment to move seedlings out before planting, but sadly I failed to monitor the temperature and all my seedlings were killed one warm and sunny day.

I learned two valuable lessons about greenhouses. A small volume of space is prone to wild temperature fluctuations and without venting it is impossible to manage temperature on warm days. This year I applied those learnings and ordered a medium-sized GrowSpan greenhouse. 9’9″ in length, 9’1″ in width and with a peak height of over 7′, it is a good size for our urban farm. It also features 4 panels on the roof structure that will open for ventilation, and GrowSpan offers a solar-powered vent opener to provide even more security against overheating.

It arrived in many bundles of parts in two large cardboard boxes on a pallet and over the course of a week, I worked on it when I had time. This is not a project you will race through, so plan on spending at least 15 hours to build it. The tools that are required are basic, a nut driver and socket, flat and star screwdriver and a caulking gun for silicone to be applied on select panels.

The retention system for the polycarbonate panels is pretty ingenious, and the fastener system utilizes channels in the framing. I was really impressed by how well thought out the system is.

What did not impress me is the documentation and part numbering. Simply put, the documentation is awful insofar as pictures of assemblies that offered little detail for orientation and fitment. It was a miracle that I managed to put it together properly. Another detail I did not like was the doors, which slide nicely but required modification to assemble. The Teflon sliders are attached with screws into the frame channel and my first attempt stripped the screw; it was only after drilling out the holes that I was able to properly assemble the doors.

I have since outfitted the greenhouse with shelving and a workbench. Over the course of two weeks featuring warm and sunny and cold and rainy weather, the internal temperature of the greenhouse has stayed constant. I think it will work out well and the initial trays of seedlings I have been monitoring are doing really well in this environment.