posted 10 years ago
I have a hoop house in similar or harsher growing conditions, and I am wondering if this might not be solvable without a whole lot of intervention.
Our hoop house now: roll up sides, sides not secured very well. (we might get to it, much more relaxed this year), already down to 8 deg
Our hoop house last year: much tighter closure, but still open during the day because we keep chickens in one end, hit -10 last year (we did throw some blankets over the veg that night).
Before I had a hoop house: 18" low tunnels made from some Home Depot visqueen and some 9 gauge wire, held together with clothespins (this super ghetto, totally not-snow-worthy system was in SLC, max low one year was 0. No venting, in fact the coldest year I ignored them from Christmas until March, when I was surprised by so much lettuce I gave it away by the sackful to neighbors.
In all of these systems, chard and kale thrive. The problem, if any, is that it gets too hot on mild days (+80 deg). The arugula started to flower in November this year! I haven't got any fabric for a second layer, though I keep meaning to get some.
What I am noticing makes the most differences: 1) variety and species selection. This year's kale isn't so robust (white and red Russian kale. I can't remember the best one just yet, will add it later to this thread when I find the notes). Black-seeded Simpson lettuce goes forever. Tatsoi is unkillable, Joi Choi a little less so but they are still looking good today. I haven't tested enough chard to know whether the Bright Lights is more tender than the Fordhook, but I think it might be. Bulls Blood beet is extremely tolerant, we use that for color in the salads. Most of the radishes got pithy, but there was some really hot days in October. The harukai turnips are still doing good but I don't expect them to go much longer.Right now they are so sweet I can eat them like an apple. The arugula is getting a little spicy but shows no damage.
Variable #2 is equally important: when you plant. Last year I planted early October, around our first frost date and that was too late. This year, I planted Labor Day weekend. I started some of the transplants around August 10. I could have started earlier, like August 1. I especially wish I'd gotten carrots in earlier, I suspect they will just linger at pencil size all winter then bolt. Eliot says the plants should be fully grown when they hit the really cold temperatures, and just go into a hiatus. They do keep growing (as observed in the low tunnels I abandoned one year). So maybe to 80% of full size is a good target for first frost. I just am not going to grow cute mesclun baby greens in the winter. I expect them to be robust, full sized and strongly textured but sweeter than the same variety grown in the spring salad mix. For us, I think it really helps that the roots have a chance to grow a little deeper.
Variable #3 is also critical: it's going to really heat up in there on sunny days in our climate. We don't have Maine's maritime cloud cover. I need to pay attention to vent every day. As soon as it goes above freezing, I'm venting if it's sunny. I don't worry about it going from 0 to 60 outside, but 0 to 85 inside is a problem. I don't care if it stays at 40 all day. If it gets hot, I water. I don't want the plant roots drying out, and they will stay cooler if wet on sunny days. Our native aridity and all that venting will counter some of the excess moisture. I still got aphids last spring, should have rolled up the sides sooner. I need to build a goose proof screen door for one end so I can vent even better. The dang geese have figured out where the salad bar is, so we are keeping that end door shut for now which makes it harder to keep it cool.
I have a neighbor with one of those fancy climate batteries (although that's a new phrase for me) and I'm sure it works fine. But we are getting plenty of productivity without it. There was a learning curve however, especially as we scaled up to the full sized walk-in system. Hope that helps.