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Lessons from the Winter High Tunnel

Winter Crops in High Tunnel

This is the first year I have tried growing crops in the winter. Since this is the first year with the new high tunnel, I’m on a rather steep learning curve at this point. I consider this entire season an experiment, so I’m collecting loads of data: how often to water, when to plant, how fast things grow in the cold, lots of good info. Hopefully the end result is a more productive winter season next year.

Here’s the top ten things I’ve discovered so far:

  • Cut-and-come again type plants seem to be the most successful. Lettuces, Spinach, and Swiss Chard are all growing at a good pace, and can be harvested about once a week or so.
  • Collards and turnips can be planted fairly late, even in November (zone 7b) and will grow like crazy. Broccoli and Kale will not. I think to have a decent winter crop of Kale and Broccoli, they need to be in the ground by mid-September.
  • High tunnels are a great place to overwinter root vegetables like carrots, onions, and leeks. These can be planted quite densely, at 2-3 inches apart and do very well. Harvest some in early winter, then leave the rest to get a jump on Spring.
  • Even in our zone, the “edge effect” is something that has to be addressed. After a week of below-freezing nights, the outside rows of the tunnel froze, even on the south side, which surprised me. Future crops in those rows will need frost covers to remain harvestable.
  • The ventilation fans need to be running most of the time. Otherwise there is enough condensation that the plants get wet. Wet, cold plants are not happy plants. I turn the fans off in the afternoon if the tunnel is dry, but then turn them back on again at sunset.
  • Because plants respire more slowly, watering is essentially a once a week thing. I also have to make sure to not over-water, because it takes quite some time to dry out. And then the spinach turns yellow (ask me how I know).
  • It is possible to replant a crop with direct sowing, but it takes forever to grow. So start plants in a warm house or germination chamber first, then move them to the high tunnel.
Frozen Bok Choi

  • Frozen hoses are a drag. So each time I irrigate, I drain the hoses when I’m done. This is a time-consuming and somewhat irksome task, but I think I have a solution: heated water hoses. These are made for RV’s and are simply a water hose with a built-in heat tape. Fortunately, our outside outlets are close enough to the water spigot that this will work. I just need to order them (they are a bit pricey). But yay for small victories.
  • Bury the irrigation lines. I was hesitant to do this because I was worried the emitters would get clogged up. Having now nipped an irrigation line at least once every time I harvest, I now understand the logic behind this recommendation. Buried it is.
  • Put an on/off valve on each irrigation line. Plants have widely varying water needs. What will keep one plant happy will drown another. Not all the beds need to be watered every time. This could probably be automated with timers, and that is something I may look at in the Spring or Summer when watering demands are higher. For now the valves work great, and they are a cheap solution.

So there you have it. Lessons from my winter high tunnel. I hope you found a few tidbits that were helpful!