In a climate that features cold winters, one technique you can use to keep your vineyard in production is training multiple trunks. Instead of a single trunk and head, you train up two trunks. This applies to short trunks on VSP-trained vinifera as well as long trunks on trailing varietals like Norton trained on a high single wire or GDC trellis. Our vines take a beating by our cold winters and by tractor damage, and an entire trunk might be killed down to a low spot on the vine. Having two trunks means that a damaged trunk can be eliminated and a new trunk trained up in its place, while the second trunk helps keep the vineyard in production with minimal losses. Of course, if both trunks are obliterated by a deep freeze, your double-trunking is for naught, but that's the risk of continental climate viticulture.
Here are a couple items to consider when training up trunks: first, have the trunks start from as low down on the the vine as possible. Photo A shows a VSP, spur-pruned Traminette vine with two trunks coming right out of the ground. On a grafted vine, you'd want to be above the graft union, but still low as possible. Photo B shows the same varietal, but the two trunks split off half way up the vine. The problem here is that if the area below the split is damaged, you'll lose both branches of the trunk and have to start from lower on the vine.
Practicing what I heard Kevin Ker (of the Cool Climate Viticulture and Oenology Institute at Brock University in Ontario) recently refer to as "spare parts viticulture" is essential. It might even be wise to keep a young sucker cane every year as a possible third trunk. In Photo C you'll see a GDC trained Norton vine with two healthy trunks, numbered 1 and 2. I've left a cane from last year (#3) as an insurance policy. It might make a great replacement trunk due to its youth and the fact that it is ruler straight while the other two trunks are a little more twisty than one would like. Straighter trunks are easier to work under without catching equipment and damaging the vine. Plus trunk #3 it starts lower down on the vine. I may just keep this one to replace one of the other trunks even if all three survive and are healthy. I'll talk more about the age of your double-trunk system in a future post.