Courtesy of Adithya Ramachandran, Kaleidoscope Vegetable Gardens, Dundurn SK
High tunnels require farmers to become their own weather forecasters. In the Saskatoon area, tonight’s forecast low is -13 C (8.6 F). That’s a little too cold for most cool-season crops, so we spent part of last week laying down row cover – 8000 sq ft of it. The cover also accelerates germination.
I’ve kept temperature records in past seasons to determine the effectiveness of row covers. Based on variables such as afternoon soil temperature at a standardized depth, number of layers of row covers, soil moisture status, and height of row covers above
plants, I came up with a few formulas for determining what the overnight low will be.
For example, today’s soil temp. at the 4′ depth is 10 C inside tunnels. I expect it to rise to 14 C by late afternoon. 14 – (-13) is 27. For a single layer, I use a factor of 0.35. 0.35*27 is 9.5. 9.5 + (-13) is -3.5 C (26 F). That is my forecast low underneath the row cover.
For double layered row cover, I use a factor of 0.45. That gives me a forecast low of -1 C (30 F). Sunflower greens are the only crop to get double cover – all other cool-season crops should be fine with one layer.
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