Hi, Ive long been interested in a pit greenhouse idea on my smallholding.
The design Im working on is a very simple pit 60' long by 25' wide and about 6' down from ground level, but making a large bund maybe 10' high on the north side with all the earth that comes out. So trees can be about 16' tall on the north side.
A cold sink trench on the south side, and a plastic bottle roof about 45 degree angel to the top of the bund.
So simple, nothing complicated. Just dig the hole and put the plastic bottle roof over it. Keep the topsoil separate and put that back in after.
My hope is that if I go deep enough that the cold sink trench will hold some or a lot of water for much of the year, I can use this to water the plants and maybe do a bit of aquaponics. Maybe tilapia and fresh water crayfish.
The main plant I want to grow is moringa, they grow very fast and can be very hardy even in poor conditions. They have a long tap root that can go down as far as needed to find water even in dry times like now. But they need warmth and they wont survive the winter here in the UK unless in a pitgreenhouse like the one im building.
My inspiration came from Mikes book, but Im not going to bother whit any frame at all, just dig the hole and put the plastic bottle roof over it. With a door and ladder going down.
Are you going to dig the hole in the side of a hill? If your plastic covering is flat ( horizontal), you won't get much sunlight in during the winter (when you need it most) and will get too much in during the summer.
The "roof" ideally should be at a right angle to the noontime sun during the coldest part of winter.
My opinions are barely worth the paper they are written on here, but hopefully they can spark some new ideas, or at least a different train of thought