Long life trellis

For extremely long life, metal.

I have two towers made from copper pipe (in my ornamental gardens) and several moveable trellises** in the vegetable garden framed with thin-wall galvanized conduit and one made from natural gas pipe (heavy). The garden trellises have webbing made from "tomato cage" fence wire, which has had to be replaced once. If I'd used concrete reinforcing wire it would likely not have needed replacing yet.

These have all lasted for many years, while some decorative PVC and treated-wood tellises rapidly declined.

A lot will depend on what you want it to hold, and how you want it to look. For small diameter stuff, probably non-corroding metal

-- copper, aluminum, galvanized steel. For heavier stuff (wisteria), thick pieced of rot resistant wood are good -- cedar, cyprus -- but not cheap.

For plant cages to hold annual vegetables, I use reinforcing mesh. It works very well, but isn't very pretty. After about a year it is dark rust colored. I kind of like it, though I suspect my neighbors aren't as pleased. The oldest I have are about 5 years. I can't see any reason that they won't last another 10.

Creosote is a carcinogen, so lots of people avoid it. If you don't care, it is also an irritant. I've never had a problem, but some people get rashes.

Personally, I haven't seen a source for used ties for over 15 years.

Hard to beat PVC. You glue it together, and it lasts pretty much forever. Schedule 120 will hold pretty heavy stuff. You could probably trellis pumpkins on that!

If the food the trellis grows is the most important aspect, then metal or PVC supporting a lattice of of wires, or wire fencing would probably give you the most longevity. If you wanted something more decorative, then I would suggest a wooden frame.

Making Bentwood Trellises, Arbors, Gates & Fences (Rustic Home Series) (Paperback) by Jim Long