The page goes into much more detail than I can here, but the jest of it is between the 1920's-1950's the Russians developed a system for growing citrus in sub-freezing climates using a number of innovations including cold-hardening, trenches (of course), and forcing the trees to grow very close to the ground. Some rather extreme, though interesting, ideas!
If you don't "know enough"... try anyway! (Cuz that's how you learn.)
Around here we'd call those 'seasonal ponds', unfortunately... unless I built a giant berm of very well drained soil and put the trench on top.... hm.
'Theoretically this level of creeping Orwellian dynamics should ramp up our awareness, but what happens instead is that each alert becomes less and less effective because we're incredibly stupid.' - Jerry Holkins
Thanks for posting that K!!! So they could grow citrus in areas where it got very cold. And the trenches were just one way they did it.
I'd wondered about digging a hole to put a lemon tree in on my property but it would've been a miserable failure the way I was thinking of doing it. This article gives me some serious hope.
They didn't say how they incorporated the small amount of glass into the trench design. I'm wondering if they just spaced the boards apart a bit and laid glass on top of it and then the mats on top of that.
Or for my situation, I wonder about a layer of twin wall poly as the roof (along with boards for support) starting when the first frosts are expected. Then it will be covered by snow for Nov-Mar and I can open it back up in the spring...
They said that roofs were sloped at 30-35 degrees but the picture made it look much flatter than that.
A government department in my region of India promoted sunken greenhouses a bit like that one year, and our school tried it out. I didn't like two things about it. One is, the south wall of it cast a long shadow in midwinter. Another thing I didn't like is that entry was by peeling back a corner of the top and climbing down inside, and then ours was too low to work in comfortably. The advantage of course is the heat of the earth.
Works at a residential alternative high school in the Himalayas SECMOL.org . "Back home" is Cape Cod, E Coast USA.
I believe the point of these trenches is to have them open for spring/summer/autumn and then cover them for the winter. Since the trees are kind of dormant in winter you shouldn't need to access them much, if at all. And the shade from the south wall also wouldn't be an issue in winter.
I assume they accessed them at the end via a series of steps or ramp that was also covered for the winter.
If the roof was really sloped at 30-35 degrees, then it would let decent sunlight in around the solstices. But the sketches sure don't seem to show them at 30 degrees.
I was looking up cold hardy citrus from Mckenzie Farms and the Owari Satsuma sounds like a candidate for this. Good down to 12F. I'd imagine that tree in a 6' deep and 5' wide trench with a blanket of snow above it would easily get through my winter above 12F. I think...