Last season i growed some my citrus in the trench greenhouse that showed below:



I didn't use any extra heat.

hi looks like a great idea,do you have any details of the temps.through the winter,inside and out,as examples! artie

Last winter we had min temperature about -25 -27 C. And we had -20 -25 C at night for one week. There were about +0,5 +1 C inside greenhouse. But my big dog broken my greenhouse early spring when was -5 C at night. My citrus got hard damages. This is the pic of my citrus after cutting dead grafts.



This pic was taken after 21 day.



This pic was taken a week ago.

hi nice to see your citrus have made a recovery,have you thought about putting double plastic sheets over it for next winter,sort of double glazing! also seen the date seedlings,ive got quite a nice one, true leaves ,it has taken 5 years its about two feet tall.artie

Yes, i have! In future i'm going to rebuild my greenhouse with double plastic sheets. In winter i used the styrofoam shields to cover my greenhouse. This summer i am building my new greenhouse. It will be deeper and more large.

Wow thats a cool greenhouse!
your tree got a lot of cold damage, but it sprouted back out fast! and now you can't even tell it had damage!!!

Sounds like a great idea --nice job!

Wow that looks amazing and nice looking plants. Hope dog stays away for this coming winter

wow that is great, is it dug into the ground and how deep

so you cover with installation in the winter?

you could also cover with heavy blankets and a blue tarp.............which is what I do for my outdoor trees in my zone 5

Frank, i covered my greenhouse by styrofoam shields and tape over styrofoam.

what was the outside and the inside temperatures during the coldest day in your area ?

Nice try , and of course I am thinking too on building such thing.

It was about +1 C inside in the our coldest day with nighttime temperature -25 -27 C. This year i have built new tranch greenhouse. It is larger and deeper than old greenhouse.

Could you give some details ...dept , length , width.

thanx , it is very very good

The tranch has 3,5 m (lenght), 2,1 m (width), 1,2 m depth.

isn't it too shallow

depth 1,2 m , maybe that's why you had only 1 C in winter , digging more will benefit from soil heat.
In my area for connecting to water pipes , the frzoen depth is 1,2 m , so it definitely must below that point

I'm thinking doing something like this only the depth will be higher , at least 2 m.

Anyway it is a perfect job for your plants