I have a question about OLD muscadine/scuppernong vines. We have a piece of property with very old very neglected vines. Some of the poles are rotted at the ground and need to be replaced to even have a chance of getting things back on track. The grape vine base is by these poles. When we dig new holes is there any way to keep from damaging the old vines? Is it better to try to start over from scratch?
You should be able to avoid damaging visible trunks without much trouble, but to be on the safe side maybe wrap some kind of barrier around the bases of the vines to avoid skinning them with your post hole digger or shovel. A section or two of old bicycle tires or some aluminum flashing held on with wire might work.
You will probably damage some roots in the process, but don't worry about it too much. Muscadine grape roots grow out in various directions from the base of the plant. Each plant will have several. They usually grow less than an inch or two under the soil surface. To avoid damaging roots where you dig, excavate the soil with your finger where you intend to dig to discover whether roots are there. If roots are unavoidable, go ahead and dig. The other roots will support the plants.
Here's an alternative. If the majority of posts are rotted, consider not replacing them where they were before. Install them instead between the vines. For example, if your vines are growing 20' apart, install the new posts half way between them. You have less chance of damaging the plants.