Pruning too much can take off most or all of last years wood. That knocks out grape production for one year but puts you in good shape for next year. Save four or more shoots that grew this year and you'll be buried in grapes next summer.

They fruit on 2nd year wood. So if you cut a vine completely back you will have to wait this summer and next for the fruit.

Grapes fruit on last years wood. You only lose one year by over pruning. Unless you over prune again.

OK - I'll just thin a little this fall. Thanks for the information.

Bejay

Bejay:

If you want best fruit and manageable plants don't over compensate with too little pruning. A balanced approach each year is best. Usually I leave about 40-80 nodes of last years wood. That's four canes with 10-20 nodes per cane. If the main purpose is to cover the arbor, you could leave more. But when more is left the management can become increasingly difficult. The grape bunches will be more numerous and smaller. Fruit quality can suffer.

I'm thinking about going out and giving mine the haircut of their lives in the next week or so. They are covered with many clusters, but I don't have time to take care of them, and I won't have time to harvest and process them anyway. Life is in the way. But, they'd be in good shape for 2012.

There are multiple ways to prune grapevines. Some recommend pruning down to leave only two buds per vine shoot, which will be where next year's growth will be. This method is great for wine grapes and encourage grapes for next year. Plenty of Youtube videos on it.

However, Thompson Seedless do not respond well to this method. They will grow fantastic folliage, as you've seen, but will not produce much in the way of grapes. There is another method for pruning these. I believe it is called caning. Basically, from the trunk you count out the lateral runner (assuming you have it on a wire) and prune everything beyond the 3rd or 4th rising cane. You decide where based on the vigor of the rising cane. If the 3rd is vigorous, then it, if the 4th more so then it. If you end up messing up, you still have the 1st and 2nd to use. Once you have cut off the lateral, you then bend the rising cane down to the wire and tie it down to make a new lateral. Be gentle, and you may hear the wood crack a bit, but that should be ok. This is where the need for riser #1 and #2 may be necessary. Once you have it tied down, then prune the risers closer to the trunk as you would have the other method, leaving 2 buds.

I couldn't find any videos on this, but if you search for grapevine pruning methods for Thompson grapes, you should find it. Apparently Thompson likes to put grapes on the vines from the upper buds only.

Good luck!

Dan