I have a vine growing up my porch, mainly ornamental/for shade in summer and a windbreak in autumn. I did get some grapes last year (a little sharp and pippy, but tasty) but my climate is marginal for them to ripen especially given that it gets quite a lot of shade. Any edible grapes are a bonus, and I've been known to stuff a few leaves as well. The vine has been in the ground about 3 years, and this summer's growth was quite prolific; I need to do something to keep it manageable. Last year I just trimmed it a bit, without too much thought. All the guidance I've seen online has been about pruning for cropping.
Should I cut it back hard? Will this keep plenty of leaves low down? Will it grow back nicely if I cut back to old wood, or must I leave some green? What time of year is best to prune?