Support for Wisteria on very large tree trunk...suggestions?
This summer, I planted two japanese wisteria on opposite sides of a very large old walnut tree trunk. The tree is about three feet in diameter and appears to have been struck by lightning before I lived on the property. The trunk has no branches except one thick (10"?) branch that reaches to the east at approximately 25 feet at the very top where the main trunk was broken off. A portion of the trunk is obviously still alive and feeding that branch and a small bunch of branches coming from the ground at the trunk's base on the north side, so it should still have a decent anchor of roots underfoot even if the west side is slowly rotting away.
The plan is for the wisteria to twine around the tree trunk, eventually reaching the top, covering the ugly bare trunk with foliage, and providing a show in the late spring. The plants were two- and three-year seedlings and have started putting out some tendrils, which I've managed to coax toward the tree trunk.
My concern is that the trunk has no branches except for the one remaining branch at the very top. I've considered mounting heavy duty bolts sticking out about 6" at intervals spiraling up the tree for the vines to grab onto, but I'm not sure if that will be adequate. Lately, I've considered screwing in heavy-duty lag bolt eye screws and setting wire around the tree, but I think it would involve a LOT of hardware to keep the wires an adequate distance from the trunk.
My fear is that if I let the wisteria grow unchecked and without support, it may grab onto the loosening bark that it will inevitably pull off, or wrap itself around the tree to a certain height and then collapse from its own weight. Should I wait for it to take off next summer and drive bolts in to support where the vines lie naturally, adding them as needed? Will the wisteria find a spot to girdle the trunk and support its own weight by itself (I'm not worried about killing the tree)?
Any ideas? I'd like to create a beautiful tangle of vines around this immense stump over the next few years...
Thanks for any advice,