Yes of course it would work. Keep in mind, the smaller the greenhouse the harder it is to keep it cool during the warm months. Citrus trees grow WELL between 70 and 90-F. With a greenhouse only 12 to 14 feet in height, you will need to plant a citrus tree that is grafted onto Flying Dragon root stock.

The lowest 3 feet of the GH does not have to be glass but could be made of block, wood, concrete, or etcetera. The ground level can be sunken a few feet. The north wall gets no sun and can be an insulated wood frame wall. The north side of your wall could be a very nice tool shed. Width from east to west is much more important than depth from north to south. In the dead of winter you will get nearly nothing on either you east or west walls. Almost everything will come from the south. A 24 foot east to west tool shed 6 feet deep with a 8 foot deep green house on the south side will give you better results than a free standing 12 by 16. If you are building your own Design I would like to suggest triple glass Argon sealed window. Make sure they are not Low-E. You need to have the suns heat pass through.

I I think I’ll probably do polycarbonate like my current greenhouse just because of costs. Does the ground need to be insulated for roots? It obviously freezes where I live, but the greenhouse will be heated. Will that affect underground? I’ve never checked with my current greenhouse because it had a gravel floor.

I agree with Silica and do the same with mine

How deep down would I have to go? The area around where I’m going to build this spring/summer is pretty level and I really don’t want to dig it up (again). I did it once to install the chicken and rabbit yards. Also, our soil is high in clay. I think this is going to be a problem. Suggestions? There’s a French drain next to the current greenhouse where it’s going to be build, so it is fantastic drainage. It used flood where my greenhouse is now, but now it has the best drainage in the yard. Is this a solution? I don’t think so, but it would be great if so.

Rootstocks for clay soil

You don't need to dig down at all. If you have trees on Flying dragon the will stay on the smaller side. If you have a choice the best rootstock for heavy clay wet high ph salty soil use Seville sour orange rootstock.

Steve

Thank you. I’d prefer to let them grow taller, I’d like to have tall trees inside.

Question, if I dig a pit down four feet, insulate the walls of the pit and build a foundation and do not fill it in again, does that do the same as filling it in for insulation? This way, I’d get extra height, but I also don’t want to pay a fortune for heat.

Anything that is sunk into the ground will use less energy than ground level. To save the most money on heating, the north wall should be well insulated and painted bright gloss white to reflect the sun back on the trees.

Thank you, Steve. You have been incredibly helpful throughout this entire process. Right now, the current plan is to dig down four feet (ugh) in what I’m currently thinking is a 24x24 square for a 20x20 greenhouse. Then, I’ll make a cinderblock foundation and insulate the inside of the blocks. Should I also do the outside? Or ignore the inside? I’m open on that. This foundation will go all the way down. Then, I’m thinking I might raise it two feet or so above ground for an added six feet. On top of this foundation, I’ll build my greenhouse. My greenhouse will be build of pressure treated wood since I’m not a metal worker. I know I’ll have to deal with the upkeep. The north wall shall be solid and well-insulated, as well as probably having my heater and other utilities. My trees will be on dwarfing rootstocks, especially Flying Dragon. Any other suggestions?

Construction will start hopefully around Late April/Early May (REALLY hoping for late April) or whenever it gets warm enough to move everything outside. My new greenhouse is going where the current one is.

It might be a bit less expensive to buy a 20 foot square kit and assemble than to buy the individual pieces and cut the wood. Treated timber twists and may break panels mid winter.

Steve

chickentimmy: Look up Walipini greenhouse on google and you will find a wealth of info on greenhouse construction that is partially underground. The word 'walipini' originates from Bolivia in S. America where it is very popular. I think this is what you are looking for.

Google "Orangeries"... how rich people in colder climates grew citrus 100 years or more ago.

Yes heating cables are what will help. I'll be adding some this fall to my GH. 20- 30 feet. It should keep the banana and citrus roots near growing temps. I recently planted some sort of mandarin orange and plan to put the meyer lemon in ground too.

How tall is your greenhouse, Matt?

Only 7 feet.. but that's better then it was LOL

I do have the option to dig down say a foot or two.

here it was during that extreme cold in Jan

How do your trees do with the cold? I know you shut it down for a while last winter, but your greenhouse is colder than mine. I had to bring the plants on the floor in over that cold stretch because it got to 32 until I bought high-quality heat mats.

Everything is alive. although the citrus that was out there lost a few lower leaves.

Jan is the coldest month with daytime highs in the 50's nights in the high 30's-low 40's. I have since better insulated and that boosted the temps 3 degrees.