Any experience-based tips on pruning and when to do it? The vine is now heading into its third year and has developed two separate branches, each about fifteen feet long that I have trained along the upper framework of the tunnel. I forget the name of the variety but last year it produced dozens of bunches of small black grapes, each with one rather large pip. I think "Capetown" featured in its name.
It's essential to prune whilst it's fully dormant or it will ' bleed'.
Year 1 after late autumn /winter planting prune back main stem hard,cut back by upton2/3rds. If there are any sideshoots cut these to 1 bud immediately above the bud- this is the same process for any pruning
Year 2, allow main stem to grow to reach the top wire. Also you can allow a couple I'd bunches of grapes to grow if growth is vigorous - 2 laterals 1 bunch each. Pinch out the tips at 2leaves pass the flower truss. Non fruiting laterals should be cut back to 5 leaves before they get too long. Tie in as necessary. In early winter after the leaves have fallen, prune the new growth on the main stem is cut back by half! The laterals are cut back to leave 2 buds again.
Year 3 & hereafter - in midwinter untie the main stem & allow it to hang down horizontally almost to the ground, support with a string to the roof, this encourages even bud break along the length of the stem. When buds start into growth retie to normal position.
Each lateral Shoot can now be allowed to carry a bunch of grapes, prune backto 2 leaves past the flower truss asbefore. Leave the strongest Shoot & rub out the othersat an early stage. Tie each lateral to a horizontal wire, but do it gradually over time.
In summer pinch back the sublaterals to 1 leaf before they become too long. Any laterals without fruits should be cut back to 5 leaves.
After harvesting the fruit reduce the laterals by half their length.
In winter after leaf fall slightly cut the top of the main stem or rod & cut back all laterals to leave 1 growth bud.
This is all taken from the Collins Aura Garden handbook, Grapes by Alan Toogood. Not sure if it's still in print, shame I cleared out my late dad's copy a few months ago, never thought to put it with my copy.
Hope that helps