I have used many different sized bags up to 400 gallon. The bigger the pot the bigger plant but it doesn’t need to be that deep, especially if you are planting clones. Now we use fence panels cut in half lengthwise and put together end, or close to that and lined with road fabric.(1st photo) That can be like a 10’ circle x 2-1/2” deep.
This year I made a couple of 3’ x 2’ pots with fence wire and road fabric.(photo 2)
That was after I filled raised beds bordered with scrap BCI floor joist. My soil is 15”-18” deep.(photo 3)
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