Answer: Grapevines are pruned during winter dormancy, shortly before the last frost date in your area. You don't want to prune too soon, as pruning stimulates tender new growth that is susceptible to frost damage. Here's a publication from New Mexico State University Cooperative Extension to download that includes line drawings: publication H-303: "Pruning Grapes to the Four-Arm Kniffin System. http://www.cahe.nmsu.edu/pubs/_h/h-303.pdf. Good luck with your grapevines!
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