Last year I had some wooden structures taken down of various ages and composition:
-- I had one built of redwood (untreated) about 13 years old that had rotted where it made direct contact with the ground, though the upper part was in good shape so it was removed.
-- A large trellis lattice fence/structure made with pressure treated wood with 4x4 posts in concrete that was 14 years old had no sign of rot at the base, but some of the upper structure had some damage due to weather and climbing roses growing through it. Part was removed only because I didn't want it there and the rest needed light repairs (nails, a few replacement boards, generally good condition)
-- Another structure also of redwood about 8 years old was in good condition and the wood reusable when we took it down.
-- A cedar cold frame at least 10 years was taken apart and the wood reused for a bird house.
-- 14 year old powder coated metal obelisk was rusted and the coating flaking away removed and metal recycled.

So I think that pressure treated wood lifespan is almost equal to powder coated metal. I like the way it looks as it ages naturally MUCH better than the rust that develops on metal. Natural redwood or cedar lasts less than the pressure treated but is better for the environment and still lasts a pretty long time. I think that would be my first choice for any new structures.

Oddly, we've had major losses in pressure treated wood that isn't in touch with the ground (or with plants), and often at the center of the wood, where the harder wood should be.

I wonder if copper tubing over rebar might be a solution.

Ann, I've thought about copper over rebar, too. I have some tall trellis work in my plans and would like the additional strength of something like rebar under (fancier) copper pipes but hesitate to combine the two. I worry that the metals coming into contact with each other might cause the steel rebar to corrode more rapidly like steel pipes corrode when connected to copper ones. Are there any chemists out there who can speak to this question?

Beaniebeagle, if it's any help, my father built a redwood fence in 1957. Portions of it served as a trellis for several plants. The fence is still standing, although most sections are propped with stakes now. Dad lives in Dallas, TX. My pressure treated trellises have held up for 10 years and are still in great shape except where our border collie attacked one. (Don't ask.) Like Lori Elf, I'd probably opt for cedar or some other nontreated wood now.

Carol in Portland, OR

How big do your structures need to be? Tom has made me lovely obelisks and trellises of copper pipe. The ones he made a dozen years ago are as sturdy as the newer ones, and only now beginning to turn that lovely verdigris color which I love so much. I expect them to last for decades. Of course copper would not be strong enough to hold up a heavy rose (or worse, a wisteria) on a monumental arbor or pergola.

Not a fan of HOAs chiefly for reasons like this. I don't ever want my neighbors telling me what to do with my garden.

Folly

Rosefolly- ooooh... I want a copper trellis... sadly, the threat of theft aside, here in 9b/14 a metal trellis would just fry anything on it or near it. I'm thinking of putting one together from my beautiful pruned crepe myrtle bits. I know it won't last as long as cedar or redwood or pressure-treated, but it's too nice to toss and I can't think of much else to do with it that I actually have the skill for!

New Girl, I don't know where you live in northern California, but depending on local conditions, you might be fine. I am in 9b/16, the South Bay area, and my roses don't seem to suffer any effects of the sun on copper structures. The big climbers in the back are trained up the chain link fence that keeps the deer out, though I must admit that fence is coated black, and the coating probably keeps the temperature down. My clematis are all on rusty iron or painted metal supports, and they are fine as well. I think where temperatures go into the 100's daily it probably would be a problem, but here where summers are mostly in the 80's and 90's with only a few days in the 100's, they work fine for me.

Folly

Wondering why you're thinking of reinforcing copper with rebar? Plain copper pipe seems cheaper than the copper tubing & is inherently strong. The tubing can be used for decorative elements or circling a pipe structure to tie it togeher - not really structural support.

With the corrosion copper causes to baser metals like rebar, believe you're talking galvanic action & are right not to combine the two. If you slip plastic tubing over the rebar to isolate the surface from contacting the copper, you may be able to avoid the situation. Might be worth researching if you prefer that construction technique. Have seen hoses & plastic tubing threaded over rebar arches before installing to give a less rustic appearance & protect from rust. They can be sealed at the bottom & slipped into anchor holes. But the rebar & the tubing must be bone dry & done on a low humidity day to guard against sealing moisture in. If you're thinking of using the rebar just to help shape the copper & not for any structural reason, don't see why its eventual flaking to nothing inside the copper would matter.

Farmers here use locust posts for fencing & char the bases that go below ground to preserve them. Enlarging a garden bed here, found a charred 10" diameter tree trunk buried a foot below ground. Took most of a day to dig & pull it out. Heard some of the trees here that were cleared off when this house was built were burned on site. It's against code to bury such partially burned wood, since it doesn't decompose. At any rate, that trunk looked as if it was petrified. Couldn't even get a chainsaw through it! So there's tradition behind this method.

Only a couple wooden garden structures over the years, since I worried about upkeep & rot. Did erect a plain untreated tall 6x6 post for a condo birdhouse 20+ years ago. Triple-coated it on all surfaces with Thompson's stain & then mounted it on a metal fence post anchor. The birdhouse fell apart many years ago, but the post still stands.

We had cedar outdoor furniture for years that we oiled annually to maintain. Without that protection, it would become rough & crack - not great for comfort. Still use the Thompson's tinted stain on the few wooden elements outside - the mailbox post, the finial for the copper ogee trellis, the handle of an iron hose reel - giving them another coat after washing down maybe every 7-10 years. It's certainly preserved them. Like the dark gray called Colonial Blue - can't see the "blue" in it, but it gives depth to the gray - because it fits in well with natural garden colors. Figure a copper cap on an upright post treated with the Thompson's tinted stain would last many years if installed with a fence anchor. (Use copper nails or screws to prevent that galvanic action.) We've used the tapered as well as the corkscrew types & they've remained sturdy. Last time we put up a bird feeder post mounted with an anchor, my husband put one of those vinyl sleeves over it & that's lasted nicely 15 years. Bears come by & shimmy the post to remove the feeder & it stays straight. I hose it down once a year & it still looks new.

Two hefty wrought-iron arches put in 16 years ago lost their original powdercoat just last year. I preferred to just oil them (oil rubbed with a rag), but my DH decided to spray them with heavy-duty Rustoleum. We'll see how that stands up. Wrought iron garden furniture needs a wire brush & repaint every 4-5 years. I may just strip & oil them next time that job comes up. Two heavy 3-fold (that store flat & pull out to form 3 sides) 5' iron trellises that came oiled still look great 10 years later with no further treatment.

My favorite for install & forget is the copper pipe. The verdigris that forms protects the metal. An identical circumference steel pipe marked for the depth desired, pounded in to create the holes with a level & pulled straight out allows the copper pipes to be slipped in firm footing. They're pricey to buy, but not difficult to make. Junk yards can be sources of used copper & other materials. Bought a bunch of those cheaply made painted metal tube arches that come in pieces for assembly with screws when found on clearance for $5 a pop. Wanted to play with arches set in a circle & figured that was a cheap way to get a 3-D model before laying out for a copper one. Left two up a couple years now & surprised they still look good apart from the screws starting to rust. Maybe I'll put them all back up, plant them & then replace them one at a time with copper while the climbing roses grow their roots. Really liked the fairy ring look.

Hope this longwinded response helps you with the construction phase of your new garden!

Here is a link that might be useful: Fence Anchors

This post was edited by vasue on Tue, Mar 18, 14 at 15:09