>>1683345>>1683418Each layer of plastic/glazing puts it into one Hardiness Zone warmer. I use two layers, so that gives me Zone 7 instead of Zone 5. You can figure out frost dates from that to calculate season extension. I can usually extend the season by about a month on each end or so with only 1 layer. I do that for things like peppers and garlics at the end of the season and with all my starts at the beginning of the season(pic). The tunnel in
>>1683042 has all the cold weather crops (chard, mustard, cole crops, & carrots). I keep 1 layer over the garlic to give them a bit of transition and extra growth time.
Some people use a high tunnel to walk into then cover the crops inside with low tunnels. They can use 3 layers so I could get Zone 8 if I wanted to. The down side is that there's diminishing returns from sunlight with extra layers. The best course of action would be to use a high tunnel with low tunnel inside then cover the low tunnel with an insulating blanket every night.
In Zone 4, you'd get Zone 6-7 depending on your non-heated setup and latitude/solar index. Adding extra thermal mass (55gal drum half full of water in the back of the
>>1683042 tunnel) also helps protect against quick temperature changes. If you add extra heat then you can grow just about anything anytime.
