January is about the latest you want to be pruning grape vines under cover, especially those that are growing in a frost-free greenhouse. The reason is because once we get into February and get a few sunny days, the sap starts rising and cuts will bleed. The aim of winter pruning is to cut back all last year’s growth to the older permanent branches, known as rods. Prune to just a couple of buds to create short growths or spurs. New growth will appear from these spurs in spring. It’s also a good idea to scrape off some of the flaky bark with a knife from the older stems as this is a perfect hiding place for many pests, including scale insects.