Due to an unfortunate accident last fall, I'm going to be restarting my two favorite Japanese Wisteria cultivars this summer in a new spot.

We have a very sturdy second story wooden deck that I'd like to train the vines along the railing of. The two cultivars, W. floribunda "Alba longissima" and "Multijuga" (aka. Macrobotrys), have white and white with lavender/purple accents, respectively. They should overlap blooming, with Multijuga starting slightly earlier, and hopefully complement each other nicely. My first thought was to plant each at a corner of the 30' railing span and have them meet in the middle and both overlap the entire span over time, but one corner would be within 3 feet of the railroad tie steps under that side of the deck (if they last another 10-20 years, I could perhaps see the vine heaving the steps eventually).

My new plan is to train them both up the same full-sun corner next to a patio over a french drain about 10 feet from the house foundation corner (about 9' vertically to the bottom railing), then train the vines in a sort of criss-crossing pattern in front of the railing (not through the railings) from the corner across the 30' front railing and around the side railing span of about 15'.

My question is...although I have seen older wisteria with several vines twining together to form the main trunk, I've not seen this done with two plants together. My thought is that the two would likely be just fine for my lifetime, but eventually (after I am not there to keep it in check) one would eventually strangle the other (in the root space and/or girdle it above ground)...before or after they pull the railing off the deck, LOL. If that happens, I'm prepared to coppice them and replace the railing along with the thick and sound, although somewhat warped decking. However, this is W. floribunda, not Chinese wisteria, which is comparatively a monster...I have pruning expertise and will be able to keep it in bounds and away from the house.

I'm picturing them planted about 3' apart, trained straight up and then cordoned to two vines on each plant roughly at the top and bottom of the railing (one each direction, so 4 total), perhaps making a pseudo archway by starting the bottom cordons lower on the plant. I wanted to meander and cross these up and down the height of the railing to distribute the two bloom varieties somewhat evenly across the front of the railing. Having this on the deck railing lets me keep a close eye on it and tie and prune without a ladder (yay!).

As long as I don't let the two main stems cross until 6-8' up, I think this should work. Anyone with experience or thoughts?

Extra credit :) Just how messy is Japanese wisteria is during/after bloom (petal fall and seed pods)...We do park with our cars' noses under this railing occasionally. And will I have problems with the wisteria water-seeking and plugging my french drain it will be next to (the perforated 4" pipe is about 3' away under a gravel base paver patio)? I can prune up top, but I'm considering sinking a barrier between the wisteria and the patio or root pruning that side on a biannual basis.

Thanks in advance for any input!