I saw one in New Mexico where they don't heat it and they grow all winter.

I can't advise you as to the benefits of a pit greenhouse, but excavating a 12x12 x 3feet deep pit would be 16 yards of dirt. That's a lot of dirt to move with a shovel and wheelbarrow, and unless you have acreage, getting rid of it could be a problem. Just something to consider.
Jim

You shouldn't need a greenhouse for lettuce in your zone. A greenhouse might even be too warm most years.

I grow lettuce outside all winter and cover it when the temps drop below 25o . It survived lows in the teens and the three day freeze last winter. I don't grow the other plants, but you might want to ask around before planting those too.

A greenhouse would be great for tender plants though and you might be able to grow lots of other things in there.

I think it's a great idea. Would you possibly need some shade cloth? Will some of the doors open for ventilation? Could I send you about 100 pots to overwinter???? please????

There is a guy named Michael on an Organic Gardening forum, who lives in Texas and has a pit greenhouse. He uses it to grow tropicals. You might want to check out his website, taroandti.com. I included a link to his pit greenhouse, below.

Lin

Here is a link that might be useful: Michael V's pit greenhouse

I can't even imagine digging that out over here in Blackland Prairie country. I watched a crew move a tree once and it was pretty much clay for at least 10 feet down and then it looked like it turned to caliche.

How cool! Darn you Brit N Rick, for now that I know about these, I must have one...

Lin thanks for the link, that is awesome! I wonder just what the equivalent zone change is in that pit, i.e could I plant my citrus trees right into the ground and not worry about them here in zone 7?

Granburyflowergirl, Michael is always very willing to help on the Organic Gardening email group (on Yahoo) so you might try contacting him through his web page and asking his advice.

Lin

I am in the process of building one in Somervell County. I am using the "Earth-Sheltered Solar Greenhouse Book" as my guide, though it doesn't completely fit with the Texas climate. My hole is 12' x 12' x 4.5' deep, and I expect to have a 7' wall on the north side. I think 3' deep is adequate as long as the north side wall is higher. Right now I'm leaning towards 6" concrete walls all around, though I may go with 8" concrete blocks just because they're easier. I want to grow lettuce, lemon grass, cilantro, and tomatoes year-round, and keffir lime and meyer lemon, too.

Drainage is the issue in my area since there's lots of limestone rock and I really want to use gravity for drainage.

Ventilation is a big issue, too, since the summers get so hot here. A friend had good experience with the temperature-controlled ventilation windows sold by major gardening suppliers so I'll probably go with those even though they are expensive. They open automatically when temperatures reach a certain setpoint, 78 or 80 degrees I think.

I will try to post pictures as things develop. Growing in Texas is such a challenge!

I started building a Pit Greenhouse late last year. I haven't had any problem keeping it warm. I set my heater at 55 degrees and it cycles maybe for five minutes every hour or so at night this seems to keep the temp between 57 and 62 degrees consistently. If anything I've had to watch the heat buildup with the mild winter we've had. If it's a sunny day the inside temperature is always forty to fifty degrees higher than the outside temperature. So in Texas I�m sure you�ll have worry more about ventilation then heating.
My foundation is four and a half feet deep and eight inches wide. I have R-13 in the north sidewall, R-20 in the roof and I covered it all with a reflective radiant covering that also serves as a vapor barrier and gives it another R-2 of insulating value. The overall size is 12�x24�. I�ve attached some pictures of the process.

Here is a link that might be useful: Greenhouse