I just planted two grape vines. I want them to go straight up into the air about 7 feet before they reach an overhead trellis that'll hopefully become a grape canopy.
A) How can I train the grape vines to go straight up? Should I drop a wire down and attach it to the ground, or put a piece of wood vertically? Or maybe a piece of rebar?
B) Should I tie the vine loosely to whatever, or will it grip on it's own?
Here's an avant-garde MS Paint artwork masterpiece to illustrate what I'm doing, to help visualize what I mean.
The grapes are somewhere between 12-24" from the fence behind them, which I don't particularly want them to crawl on.
The fence behind them is hog panel, but covered in chicken wire, and only goes halfway up. I figure the chicken wire would, long term, girdle the vine if it tried to crawl between them.
The "trellis" above the grapevines I haven't built yet, but will just be hogpanel supported by 2x4" or 2x6" joists, held up by 4x4 posts.
Grape vines are tough, if they grow into a wire fence they should be fine.
That being said, you will probably want to be able to prune them hard every year, so a wire support might not be a good idea.
I would probably use jute line and half hitches to secure it.
We just use bailing twine, tied somewhere convenient near the top of the young vine, and then tied up to the cordon wire. Admittedly the cordon wire on our trellis is only at 110cm, not 7 foot. Consider bringing up at least two canes as trunks from near the ground, in case there's a problem with one.
Until it grows to where you want it, when everything is totally bare in winter, prune off everything except the few best top canes. Be brutal, if the vine is healthy it will be fine. And think about how you're going to prune your vine up on the trellis. Remember you only get grapes on that season's growth, so you keep last season's growth only to determine where you want this season's growth to be. Then, once the new shoots start to grow, you again remove every shoot that isn't where you want it, it's much easier when they're young and green, and you can just pop them off by hand.
For context, we're on a vineyard, with about 10,000 vines. For cane pruned vines, we leave just 2 canes per plant, about a 3 foot long.