Unfortunately, I haven't updated this as frequently as I intended to. I'll try to catch up and retroactively add some pictures, lessons learned, successes and shortcomings.
How much protection did the greenhouse provide during the winter?
I recorded the daily min/max temperatures from last December through June. The greenhouse seemed to provide approximately 2-6F degrees higher minimum temperature, as compared to the minimum temperature as recorded at a weather station a quarter mile away. A thermometer that records temperatures every few minutes, and a similar one outside the greenhouse, would give a lot more useful than the simple min/max thermometer that I have, and wouldn't have been much more expensive. Last winter was exceptionally mild, with only 4 days with temperatures below 30F at the nearby weather station I used for my exterior temperature data. On the coldest night, it was 27.2F outside and the inside of the greenhouse saw 30.7F.
Outcome of overwintering efforts
Many chili plants succumbed to cold damage after the night when the greenhouse got down to 30.7F. Several appeared to be limping along, before dying back fully weeks later. Three Chiltepins survived just fine, as did a couple of capsicum annuums. My largest "habanada" (heatless habanero variety) died, which I suspect was due to my leaving fruits on it to ripen throughout the winter.
Several from-seed citrus trees between 1 and 2 years old, and a 2-year-old avocado survived these temperatures.
Seed Starting
This was the first year that I had the greenhouse space for seedling starting. For some plants, this worked very well, for others not so much.
I pre-germinated tomatoes and peppers on a heat mat in early February, and by mid-February, I had potted them in small pots and set out on their own in the unheated greenhouse. In retrospect, this was probably too early to put them out in an environment where it was getting down close to freezing most nights, because they just sat there and didn't grow at all for a month or two. But they survived and did very well once the days got a little bit longer. Peppers got off to an even slower start, probably because the soil mix I was using for them (approximately 3 worm castings : 3 coir : 1 perlite) was too heavy and moisture retentive for such cool temperatures and low light levels, and never was able to dry out to the levels that they wanted. When I repotted them in a sandier mix, they did much better.
Ironically, some of the best tomatoes and peppers were unintentional
volunteer plants that sprouted from worm castings from my worm bin. Peppers and tomatoes were the most prolific "weed" coming up from everything that I used the worm castings in. I saved some of the most vigorous pepper volunteers, and they eventually became my first ever successful bell peppers. One of them went on to live its life in a large "rootmaker air pruning pot" in the greenhouse throughout the summer, and is now 3 feet tall, very bushy, and has produced at least 6 grocery-store-sized red bell peppers and is in the process of ripening two more as of today, November 12th.
Starting cool-season crops mostly did not work very well. I started brassica, lettuce, and similar around March, planting them out in the ground through April and early May. For the most part this resulted in two outcomes: 1) plant gets immediately devoured by slugs (or it doesn't start growing quickly enough, and gets slowly devoured by slugs), or 2) plant immediately bolts (I think this may have had to do with the seedlings being exposed to too high of temperatures in the greenhouse, and then being planted out into cooler weather, thus triggering the "this is the second year, better make seeds right now" response). Regarding the second problem, the greenhouse was overheating drastically, hitting 90F+ degrees any sunny days from February on, even with the door open. In April, I had enough of 105F+ days, and got a 40% shade cloth that I attached over the outside, and which I left on through approximately October. I think that putting the shade cloth on earlier (and even rigging it up to be able to retract it on cloudy days, maybe) could help with the poor-quality cool-season starts, as would figuring out the right timing for starting them and putting them in the ground.
Early harvests
I had a lot of large grow bags and containers in which I planted warm-season crops very early. Many of these had good success, at least initially, and fruited vastly earlier than conventional in-ground outdoor growing. For instance, I germinated zucchini at the beginning of March, transplanted it Mid-March into a 7-ish gallon nursery pot filled with rotted wood chips, worm castings, weeds, and potting material from last year, manually pollinated the first flowers in early-mid-May, and harvested the first (10-inch) zucchini on May 20th. This is an earlier harvest than I would otherwise have even been planting a zucchini. These early zucchini plantings produced a few early fruits, before being rapidly obliterated by powdery mildew. A similar progression happened with cucumbers, with a smallish early harvest (which I had to hand-pollinate), and then obliteration by disease.
Attack of the spider mites
I made a mistake and plated scarlet runner beans in the greenhouse. This resulted in a massive wall and
canopy of dense foliage, and a total of two bean pods, due to the pollinator requirements and pollinators not finding their way in through the door and the vents. The canopy was nice once the sun got more intense, and really kept the temperatures down during the hotter months. Before long, though, these were also obliterated, this time by spider mites that had completely defoliated the entirety of the beans, cucumbers, tomatoes, and the second round of zucchinis I had planted to replace the ones that died from powdery mildew. I had exacerbated the spider mite problem by trying to water things
less, thinking that I was preventing fungal diseases. After an unsuccessful few attempts at using neem oil to halt the spider mites, I solved the problem by watering everything heavily each day to reduce drought-stress, and by blasting every plant daily with a hose sprayer nozzle.
Cucumbers that you don't have to hand-pollinate
In the late summer, I shelled out for the parthenocarpic gynoecious greenhouse cucumber seeds (variety called Socrates, costing an exorbitant nearly $1 per seed). I believe these were also supposed to be resistant to the diseases that destroyed my previous two rounds of cucumbers I had tried. These were truly a morale-booster on the cucumber front. They delivered massive yields without any hand-pollination, and continued production until last week when temperatures in the greenhouse dipped to 31F. The downside is that since these set fruit without pollination, they really make no seeds, so I am stuck paying $1 per seed if I want to keep growing them.
Greenhouse is a lot of work
I guess I expected this, but since it's a mostly closed environment, diseases and pests can make quick work of destroying things. Monitoring the temperatures and watering things all the time are a pain, too. Doing a greenhouse this way is not really a good way for a lazy person to garden. There are probably ways one could do some of this smarter to not have to work as hard at it, and set up better systems that require less intervention all the time. But maybe that's also just inherent to growing in a greenhouse.
I will try to write soon about what I have going through the winter, and my plans for how I'm going to more successfully keep tropical stuff limping along through the cold weather.