Building a small production greenhouse

When we rebuilt the house one thing we decided to add was a small greenhouse. We picked a spot with great sun exposure and a convenient pre-existing wall and built a small glass and granite building. The same architect that designed the house remodel gave it some nice touches too.

We added a metal table with automatic watering above it on the taller side, which is where we do most of our reproduction work and left the smaller side for mostly potted plants. In the middle we built a wood walkway between the two doors.

The last change we've done is to add some benches to the smaller side and extend the watering system to that side as well.

We've been extremely successful at doing all sorts of reproductions using this greenhouse. For example we start all our tomatoes from seed we collect from the previous year's production (that's only possible because we use heirloom varieties from the The Real Seed Catalogue and not the usual hybrids).

Last season we had a tomato plant grow out of the ground by chance. We let it ride and it fruited well past the normal season (we ate the last tomatoes in January). After that much success we decided to start planting some tomato plants on the greenhouse ground to get a small but out-of-season crop. We used the low side of the greenhouse and added a watering line on the ground as tomato plants supposedly don't like to be watered from above. That also went well but it was always a small crop. That eventually made us want a much bigger greenhouse to have much more actual production instead of nursery...

After shopping around quite a bit we found a local supplier that would build a 14 by 4 meter poly tunnel for a very reasonable price. We decided to set it on the edge of our forest garden in a spot with good sun exposure and that also helped with bringing some immediate wind cover to a somewhat exposed part of the field. The construction was all done in a single day last summer. The builders brought most of the structure pre-built with them and the day's work was mostly assembly. It started early in the morning with the setting of the posts. This was done extremely quickly with a gasoline powered drill. They were pre-prepared metal posts with a cylindrical concrete base that was buried for stability.

After all the posts were level and straight the pre-bent arches where slid into place and bolted on.

Once that was done they dug two trenches on either side of the structure. This was done by hand and was by far the most grueling part of the job, especially since the sun was high and hot by then.

Once that was done they unwrapped the main length of plastic and stretched it on top of the structure.

After the plastic was over the structure they stretched it firmly and held it in place by placing it in the two ditches simultaneously and filling them back up with the soil that had been taken out and pressing it in stepping on it. Once it was stretched they bolted it to the end arches. The next step was to assemble the frames for the doors on both sides. We opted for a single door on one side and a double one on the other so we could fit the electric buggy in if we wanted to.

Both the single and double doors have a window above it that can be closed or held in place in one of two positions. Here the winter position is shown, giving some ventilation but not facilitating the egress of hot air. The summer position is swung the other way round so the hot air rising is naturally driven out. All the doors and windows have rounded corners but are set into square frames. This leaves enough of a gap that even if everything is closed (for the coldest part of winter) there is a decent amount of ventilation.

After the build was complete we drove the electric buggy through the double doors bringing a very large amount of compost from our large piles. After spreading it evenly we planted the first crop, using cardboard to create walking paths in the middle and sides.

The cardboard worked well at controlling weeds but started to waste away relatively quickly so we used some weed barrier fabric to cover the paths instead.

To water the greenhouse we started out with a simple square lawn sprinkler driven by a water timer. This worked fine in the beginning but once the plants started growing the sprinkler would often get covered by plants and not water everything evenly. We've now installed a new overhead system. We'll do a separate post detailing that.

We've been having great success with all sorts of vegetables so far. The first tomato plants have just been added and we'll see how that goes. This is not just for annual crops though. There is a selection of tropical plants in pots about to be put in. The selection includes banana, annona, papaya, mango and a few other smaller stuff. The banana may be pretty marginal but we think we have a shot at getting a crop from most of these even if it's not every year. And that's even before exploring some of the passive heating options out there (long but very interesting video).