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).

The tomato season is on!

Winter always seems too long and in January we have all those seeds patiently saved from the previous season, plus the packets with the new things we want to try, and little patience to wait for warmer days. In previous years we have sown our first tomatoes around January 20, but sometimes those early trays take so long to germinate that the seedlings are weak and easily surpassed by the ones sown a month later. 

This year, however, we had such a cold, rainy winter that we did not even consider starting anything in January. But as February went by with one rainy day after the other we counted the days and worried about all the work that was being postponed: soil preparation (impossible to do with soaked soil), sowing, transplanting. By February 15 we made a trial with our most robust tomato seed, and on the 22th we took the chance to prepare some trays and try to start the first sample of our favourite and also some new acquisitions. 

There are two ways we sow tomatoes: using old styrofoam trays (they are put away at the fishmongers) or the regular sowing trays. In any case we fill them with a germination substrate we buy at our vegetables nursery. If we use our regular soil it is so full of seeds we get all kinds of weeds germinated well before the tomatoes! 

So the first step is to fill the trays: the substrate comes dehydrated and compact, we have to loosen and hydrate it. After that it is easy to fill the trays and compress the soil in each cell.

Just to be sure we gave most of our favourite varieties a try, we prepared two 8x5 trays. We chose 8 of our tried-and-true varieties and also picked some seeds from the 8 new varieties we have ordered this year. For weekend gardeners, it is really insane to test for 8 new varieties in the same season, but as we go through all the wonders in the Real Seeds website, it becomes very hard to resist...

It is easy to get all the seeds mixed up, so we always prepare the labels and label the rows in the trays prior to laying the seeds. In this case, we used tongue depressors (also used for beekeeping tasks) cut in 4. The little white plastic labels are nice and easy to reuse but we buy a bag and they are soon spent. We need larger packs.

When each cell has its seed, it is time to slightly bury them (we learned the layer of soil on the seed should be approximately twice the size of the seed). Now there is a problem with seeds in the greenhouse: mice are hungry this time of the year and they like seeds. So some times we wait, nothing sprouts and we see that the seed is no longer there. Not so common with tomatoes, but almost certain with pumpkins, melons and watermelons: their favourite! So we already have some hardware cloth folded to the size of the trays. They can be left until the seedlings are 2-3cm high and there is no seed any more. By that time we have to be careful with snails, but we will talk about them later.

Now it's time to select a good spot on the greenhouse table, check the irrigation timer, and hope the next weeks will bring some sunny days. The greenhouse is not heated, but keeping the door shut and taking advantage of the longer days we have now, our average temperature in the past weeks has been 12.5º C, with 10º C minimum. Tomato seeds would appreciate some 5º extra, let´s see how they will do.

It has been a week since we made this sowing, no seedlings have sprout yet. But we expect to have some next weekend. As we have lots of seed from last year, we have put some in a pot a week prior to these. It has 2 weeks now, and a regular hair of good looking seedlings. 

So we are optimistic about our first batch of 16-variety tomato seeds.

We need these tomato plants to develop and leave rooms for all the other vegetables and flowers we will start in the greenhouse. We are just beginning the season and the table is already well stocked: besides the two tomato trays, there are two large styrofoam trays with our most common varieties: the large oxheart which are cherished in the neighbourhood and the heavy-production plum tomato we use for preserving and making sauce. Another tray is starting our first parsley. Two trays have echinaceas sown in autumn: they overwintered in the greenhouse, died back and are now sprouting. Hopefully in two or three weeks the weather will be warm and we will be able to take our seedlings outside, start new batches and get room for basil, zinnias, scarlet sage, ...