Cement if you can afford it. 4X4 pressure treated lumber if not. You can also sink some cinder blocks 1/2 way into the soil and pour cement into them. You can use liquid nails to attach a 2 X 6 to your foundation, then screw the frame of the HFGH to the 2 X 6......

Do you live in a hurricane area? A foundation is different between Southern Calif and New Orleans....

jack

And what foundation would you recomend for Southern California, I am in the Southern California Desert. Wood here Dries out very quickly here. (It makes building with nails impossible because the wood will dry out and pull away from nails, Must use screws instead) I Have noticed that a lot of the wooden structures that I have built in the past few years hear have dried out and started warping.

Now Gardenerwantabe built his on top of a 4x4 wood frame, I was wondering about building a 4x4 wood frame, either inside or outside of the "Steel Foundation" or what I think of as the skirt?, and then burying that, like they show in the 10x12 instructions, I agree that the "Steel foundation", does not really seem durable enough to just be buried by itself. But with the Height of this thing, the last thing I would want to do is make this thing any taller. I know that sinking this thing into the ground any more than the Height of the "Steel foundation", is not feasable because of the door, but I do not want to elevate this thing any either.

ALso in looking at the instructions, it appears that the "Floor plates", (Parts 1-6), should be at or just above ground level?

What you do with the foundation depends on what you plan on doing for a floor. I will be using a few inches of sand then lay patio blocks for a floor. If I had buried the timber then the blocks would have been up on the side wall.
I guess you can build a foundation many ways but gluing it together with liquid nails is one method I would not consider. When the wind blows hard I don't want to depend on glue to hold my GH in place. It may work but it's not for me I used 1/4X 3" lag bolts every two feet plus two in each conner and used flat washer to assure that the bolt heads don't pull through the metal. I secured my timber by driving fence posts into the ground in all four Conner's.
I used stainless steel bolts it will last longer than I will.

Hi Darrel and the rest of the group. I too have just ordered the 10x12. I'm looking to put a base underneath it. Thinking about building it like you would a deck with posts and a rail(2x6) and cap (2x6) on the posts so it sits right at ground level. Any input?

You can make a quite robust base material using cement and subsoil. It won't be as strong as concrete, but a lot cheaper to buy, cheaper to transport (as the subsoil is already on site :). I used 10% cement in our sandy subsoil for a garden path which lasted 5 years (until we moved). When you add the cement the soil stops being affected by water.

With the right ingredients it is porous, making drainage easier. (Some people mix organic matter such as mulch into the mix, which rots out fairly quickly leaving an interesting texture and making the whole thing porous.

The hypertufa forum is full of recipes for cement stabilised earth.

You probably want a bag of concrete under each corner.

So lemme get this straight... for the "floor" inside your greenhouse, you mix in bags of Cement (The powdered stuff), with the existing soil? rather than mixing with sand, gravel and water in a Mixer?
Do you just till the powdered cement into the Soil?
Is that 10 perent by volume, IE for a 10x12 area at 3-4 inches deep (about 3 cu yards), I would use about a 1/3 of a cubic yard of cement?
How deeps should I plan on going 3", 6", 12'?
Sounds nifty, does it surpress weeds I may want to try that in my xeriscaped areas where I have weeds growing up through 12 inches of wood chips with zero water...

jimmydo: that's basically it. Depending on the cement rate plants will grow in the material. I've grown daisies in the side of a polystyrene wall rendered with CSE. It will certainly grow moss (which may or may not be a good thing in your eyes). Like anything involving cement, you will have an end of life issue in getting rid of the stuff, but if you use only a little cement (say 5%) for the bottom half, and more for the surface you might be able to use less cement overall and be able to recrush the lower stuff into soil or clean fill.

By embedding organic matter you can get nice 'ancient' looks to anything you make this way. You can use less cement if you add reinforcing material such as nylon fibre or rope.

I suggest you try it - perhaps make a garden ornament using some cheap plastic container.

Sounds like a very good way to go. I am going to be doing my foundation as a hybrid of the method sugested in the instructions.
I will be excavating an the area for the greenhouse so the foundation can be sunk in the ground.
Since the area I will be putting it in is slightly sloped, the door will probably be close to flush with the ground (or at least the pavers that will be going between the greenhouse and the patio. The back of the foundation may only be sunk about 3 inches (externaly, because I will be leaveling the ground inside the greenhouse). Electrical, water, and the drier venting will be routed underground, under the base frame.
After setting up Gardenerwantabe's corner reinforcements, I will be sandwiching the foundation frame between two 2x4's and then buring the frame/foundation. I think that if I use this suggestion of mixing the cement with the soil, it should help to anchor the foundation. If the cement/soil mixture is not going to be water porous, then I might run a drainage pipe under the wall as well so that I will have a gravel covered drainage pipe running down the middle of the greenhouse.
Now I just have to wait for the soil to dry out so I can till the ground to excavate. (It has been drizzling all day now, but at least it will make digging up the sprinkler head I have to cap, easier). I feel like I am building a celler for the greenhouse. Perhaps I should rent a Bobcat ;) it would take about an hour to dig out a 10x12 area to 5 inches

the porosity depends on the soil more than anything. There is a burgeoning market for 'porous concrete' to reduce storm run off, and the basic magic is using suitable bulk materials. Make some CSE now, and see what it's like so you can plan your foundations.

We are going to start building our 10x12 greenhouse next weekend. I have many questions after reading so many posts about the Harbor Freight Greenhouse. We have a cement foundation put put the greenhouse up on so I'm hoping that's a good start? Since my husband and I have never built anything before we are looking for whatever advise we can get. How do we secure the foundation to the cement? What size nuts and bolts should we use? Can we make the building more secure?