[Market-farming] High Tunnel Winter Growing

Harriet Allen hattie_allen at yahoo.com
Mon Nov 23 14:32:29 EST 2009

I'm growing in a hightunnel with only one layer of plastic.  I'm in Zone 7 and like the Wiedigers, I grow all winter easily.  Eliot Coleman is in Maine and that ain't too warm! He may be Zone 5 at the warmest.  For Zone 3-4 growing, I'd just stick with hardy things, but you will still experience very warm temperatures inside the high tunnel during sunny days.
yes, the growth slows way down, but I also found that if I allow the high tunnel to heat up pretty well....to around 80 or 85 during as much of the day as possible and cover more tender things like lettuce with row cover and hoops inside the high tunnel--just during the very worst of the winter here--that I DO experience growth because the ground stays warm enough for plenty of activity.  Not a lot of growth, but close to 1/3 of what I'd get outside of the 10 hours or less of sunlight.  Ten hours and less...you'll get little growth, but you'll get some and especially if you let it warm up.  I ALWAYS vent the house, no matter what, but I vent it much less than I used to when the days are cold, dry and sunny as I want to capture as much heat as I can.
The killer days are the overcast, wet days.  You have to vent because of the humidity and there is no sun to help warm things up and that is a drag with absolutely no heat in the house.  
In my Zone 7, I'll be growing carrots, spinach, mustard greens, turnips, parsley, dill, cilantro, scallions, starting leek plants, arugula, pak choi, hardy lettuce varieties under more cover, etc.  I'm very late getting my high tunnel planted this year and still harvesting lots from outside under rowcover.  But my high tunnel will bring me very early harvests as the day lengthens...By February the growth rate will increase a lot.
Coleman has done the work and the calculations.  If you read his books, or at least get most of them for references, one or the other will have the info that you need, including how to translate it to your particular situation.
Oh one other really important tip from the Weidigers.  DO NOT use raised beds in the high tunnel.  Keep them flat and they will stay warmer.  Cold air sinks and it will sweep right across those beds that are raised--and your soil will cool down, but if you snuggle the rows down into the ground at the surface, they will stay warmer.  It works.  They tested it and so have I.
It is my theory that the soil warmth is what makes all the difference for growing in the winter.  Warm soil and a layer of agribon on hoops over the soil will keep many things from freezing in the most frigid of weather.  The agribon will develop a film of ice from condensation and this will serve as insulation for the vegetables in the warm soil below.  And it is not necessary to use heavy row cover.  In fact, that can be counterproductive.  The heavier cover traps the cold air and those beds take longer to warm up during the day after a cold night....at least that is my experience.  I no longer use the heavy stuff at all.
Take the row cover off on nice days if you can.  Helps to ventilate and just to give everything more light.

Hattie's Garden
31341 Kendale Rd.
Lewes, DE 19958
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