2 answers

  1. Definitely the 2x6x12. A 1x6 might be sufficient if you're building a trellis 5 foot long or less, but just isn't enough support for a 12 foot span. You should also set your supporting posts (4 x 4 or larger) at least 2 feet deep. And setting the posts in concrete will provide more stability and help protect wood from rotting.

  2. Welcome, PatrickGambone! That sounds like quite the project! Our neighbors have a trellis in their yard-it is really beautiful in the summer. I will check with our outdoor expert for an answer on the best size beams for you. Check back soon for a reply.