Follow along with what I did, or adapt it to suit you own situation and materials. As you can see in the third photo, I had on hand a pile of lath left over from our neighbors' remodeling project. My purpose in making this trellis was half getting ready for the spring garden and half spring-cleaning by using up that pile of lath! The full lengths were four feet long, which determined my final design. If your materials or the plants that will be climbing on it push you to interesting modifications, post pictures or comments!
My trellis turned out to be 4 feet tall and about 8 feet long when fully extended, and probably took about an hour and a half to make.
The Two Main Ingredients
This trellis is composed of the following components: a lattice and two legs.
Step 1: The legs
The rest of each leg is made from a 2 foot base and an 18 inch diagonal support.
Screw the three layers of the vertical together, then the base and the diagonal. Trim the corner of the diagonal that sticks out beyond the face of the vertical so that the lattice won't catch on it.
Pre-drill for the screw that will be the upper lattice attachment. This should be at 3 feet 6 inches up from the bottom.
Step 2: The Lattice
The laths need to be joined where they will overlap but still be able to pivot. I had a box of machine screws from some unknown prior project which I used. I pre-drilled half of the lath wide enough so the screw would turn freely in the hole and pre-drilled the other half smaller so the screw would bite. You could also use nuts and bolts, but if you don't have them laying around that might make for an expensive pea trellis. You could also pre-drill the lath, push a nail through and bend it over. This is, after all, a garden prop we're making, not a fine cabinet!
After all your laths are cut to length and pre-drilled, lay them out with half as a bottom layer angled to the right, half as the top layer angled to the left. With a bit of fiddling you can line them up as in Fig. 1. Then join 'em with your hardware of choice. Come to think of it, baling twine or wire would probably work for that as well. Heck, whittle some pegs from branches to join the laths. And if you do, please post a picture!
Step 3: Join the Legs and Lattice
Make sure to attach the lattice on the face of the leg where it won't run into the diagonal brace!
I bolted the lower attachment point on loosely so it would slide. (Don't you like the wooden 'nut' I used since I didn't have a proper one to fit that bolt?) However, I find that the bolt skews easily and locks up when I try to expand the trellis. Next time I'll try putting a nut between the lattice and the leg so the bolt won't wobble and the nut and washer on the other side of the leg won't drag and lock. Or maybe the wooden nut and washer aren't needed at all. Hmmmm, things to try.