When is the best time to prune kiwi vines?

I have some of those frost-hardy kiwis, three years old (one male, two female). They have intertwined themselves in the back chain link fence, and I'd like to train them over a (yet-to-be-built) pergola instead.
When should I prune the vines, how aggressive should I be? I suspect that they ought to be no more than a year from starting to set buds/fruit, so I don't want to thwart my efforts at getting another "snack bush" for the kids.
Thanks, Mark
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very aggressive, but it is much better if you do it in the fall. you should not do it in the spring under any circumstances. Pruning in the summer is OK, but a waste of resources, specially before they have started fruiting. When you prune them, you can take out 2/3 of the vines, but of course leave the main branches alone. Make a big pergola, and do not count your chickens yet, my kiwis took 7 years to fruit.
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