Here are the ring forms. The inside 1 is 4 different quadrants so they can come apart easier. I made clips out of spare decking to hold the outer form. The first few I poured in the garage then rolled out. The first one made it fine, the other two broke. I’m more surprised with the one that made it, but I did let it cure a lot longer than the ones that broke. The broken ones broke in four equal quadrants, so I put them together and their actually fine that way. Now I just pour them in place anyway. Best to make these way ahead of time. I also used fiber reinforcement in the concrete mix. ($10 a bag from Amazon, only need a pinch for this) When ready to plant, I fill them with a mound of topsoil due to poor drainage. If you made a ring out of carboard and filled it with a topsoil mound, you could probably use that as the inner form then place an outer form around it and pour in place, then just leave the cardboard. I might try that this fall.
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