Grape vines will cover a structure like that fairly thickly over the years, might be hard to prune and maintain. I built a simple 4 posted gazebo once, planted four seedless grape vines at each of the posts, and over the years trained the grapes over the top, which had a loose lattice cover. The grape vines covered it in around 5 years, so you could barely see the structure below. It was useless as a garden house, because the birds were thick above it, leaving a mess below. The more over grown and dark it became, the more spiders took over inside, until the children avoided it. Without pruning and thinning, the grapes were abundant, but with really small berries. Only one of the grape vines had grapes worth eating, but it was the birds favorite as well. Luckily a windstorm blew it over, and we replaced it with muscadine vines on a trellis, which is pruned, thinned, and trained regularly. Adding the other annual vines the first few years sounds like a great idea, as long as the grape vines have lots of air around them for circulation and sunlight. The link below has instructions for rooting grape cuttings, but IÂve had good luck just sticking them two nodes deep in a large pot of potting soil. Let us know how your project is progressing. Here is a link that might be useful: Growing Grapes from Cuttings

I should mention that the arbor is 45" wide, 85" high, 25 deep. I am also in the Boston area so if you have any suggestions on beter grapes (aside from the Venus and Jupiter) for my area, I am all ears. My hubby loves Concords but I hate them!!

divertate- Interesting question. The way they used to treat lumber was with a copper-arsenate product, and this has been generally discontinued due to toxicity concerns. The new compounds are considered safer, but they still aren't something you should sprinkle on your cornflakes in the morning. Below is a good link that explains this all in a little more detail. I'm also a little uncomfortable with using treated wood around things I consume, particularly when the roots can provide uptake of the chemicals. You might want to consider some alternatives: 1. Dig large post holes, Pour several inches of concrete in the holes, put the treated posts in the holes and finish the concrete pour. I would think that the migration of the chemicals through the concrete should be minimal, and that there would be relatively little chemical transfer between the surface of the posts and the grape vines. However, if you wanted to be absolutely sure, you could encase the aboveground faces of the posts in cedar boards. 2. Get those steel U-shaped brackets that can be bolted onto the bottom of the posts and set them in concrete footings. That way you don't have to use pressure treated wood at all. Here is a link that might be useful: Pressure treated wood

I am not sure if moonflowers are as aggressive as morning glories but I would say it is probably not the best mix. I'm sure there are people who have combined them successfully. but in my experience morning glories are way too prolific and would totally cover your clematis by fall. It might be OK with a really vigorous clematis.