No, I think most of us have gone to 10-12". But it depends on the ground under your bed. If you have a reasonable bottom then the roots can expand into that as needed. Those of us who have solid bottoms or really crappy soil that the roots can't penetrate, wind up raising the box higher. I have clay and ROCKS in my yard so my beds are 12" high.

Best of Luck!
Susan

OOh, I thought of an exception. If say you wanted a bed to plant only smaller sized plants. Like maybe lettuces, radishes, herbs, or something like that. THEN, you could do a 6" depth probably successfully. But for larger plants like Tomatoes, Eggplants, Okra, squash, Brussel sprouts, the list goes on... you'll need more soil for that.

Hope that helps!
Susan

Thanks Susan, Thaqt's the idea I was getting from what I was reading. I have clay and rocks too. Kathy