Well, it turns out that I didn't have any scrap 1" PEX, so I bit the bullet and spent the $40 to put together a 10 foot square out of 2" PVC DWV Pipe. If this fills up with plants quickly I'll make a second one and see what happens. I opted to add rubber splice connectors at each corner so that the corral could be broken down and stored more easily through the winter.