I wonder what you mean about training them to go up the side of trees. Do you mean live trees or do you mean saplings cut down and used to make tripods? I would not advise training beans on lrees. They will not grow well in shade or among roots of a tree.

I make a free-standing trellis about seven feet tall, which is about as high as I can reach for harvesting. The bean stalks will grow taller that that and just flop over the top and hang down, which is fine.

See the link below for trellis ideas.

Jim

Here is a link that might be useful: Bean Trellises

We use 10' long concrete reinforcing mesh leftover from a construction project. It's very rigid. First my husband pounds steel stakes in ground. Then, while I hold the panel is place, he attached the panel to the steel stakes in two places with heavy duty zip ties.

We can leave these up all winter. The yard long beans seem to do fine.I think the panels are 5' high.

I use 8-9 foot bamboo poles with the side branches left on, and insert them in a double row t form an "A" shape (well, an inverted "V" because there is nothing to link them together in the center).

Works great, because the side branches on the bamboo gives plenty of place for the vines to twist around.

Thanks for your advice! I will try and find some tall bamboo stakes.