No, Chris, that's not at all necessary.
You can make it "roughly" curved by making very obtuse mitres from, say 10" boards, but have three layers where the pieces overlap brick-wise to make a 3-ply faceted blank You can then refine the curve from there.
No mould required, maybe not even a template, although a template would help to cut the individual bricks out. I made an oval cheval mirror that way and it was very successful. Lots of long grain overlap for glue, very strong result. Virtually no short grain. Easy to manage single-handed, too.
IIRC I made an MDF template for the oval frame, made the centre layer first, gluing the ends together with superglue. Of course, that is not very strong so I screwed the template to that centre blank, a screw through every piece which made it much stronger. I then flush-trimmed it on the RT. I then glued the next layer on, staggering the joints and I could see to make sure that no part of it would be left uncovered. That made a fairly strong two-ply blank. I flush-trimmed that, too. Then I unscrewed the template and laid on the last layer, covering all the screwholes. I bet a similar technique would work on your larger scale.
I know that both ways have a great deal of glue involved but seeing as this is going outside I feel that lamination would stand up to the weather better as there would be less conflicting movement in the layers of wood involved to break down the glue line.
I think a proper bent lamination would be best, but I think this is a very practical solution, also.
