I built this garden trellis arch with 4 pieces of 10ft 3/4" EMT. The arch is 78 inches wide and 7 feet tall. I used the bend calculator for four segments to help measure where to bend. Then I started at the end of each 10ft length working down until they were each curving 90 degrees. I joined them at the ends of each bend with basic couplings from the hardware store.
I determined the appropriate height by holding them upright near the barrels. They were too tall at full length so I cut off 14 inches from each leg and used those pieces for the cross beams with Maker Pipe t-connectors. The full width is about 18 inches as a result. I added two extra cross beams from some spare EMT I had around so there are 6 in total. It can support my weight if I hang from the center of the two arches, so I'm quite confident it will comfortably host the two passion vines growing up it now!
The trellis material is just a single roll of green plastic garden netting which I "sewed" on with twine and then cut off the extra. The soil in the half barrels seems sufficiently deep (20") to support the arch without the need for extra attachments, hopefully!
