Edelweiss can fruit alone, but it still benefits from a partner. Most grapes can fruit with their own pollen, but a second nearby grape with overlapping bloom can still improve yield and gives you backup if bloom weather is uneven. It flowers in early-mid bloom, which is worth knowing if you add a second tree later. Usually grown in USDA zones 4-8.
No single variety stands out as the obvious partner, but that is not a problem here: Himrod, Reliance, Somerset Seedless, Canadice, and Concord all bloom close enough to work. There are 5 more in the list below. Pick whichever your nursery actually carries. If you add a second grape, keep it on the same arbor, trellis row, or nearby support so pollinators can move easily between blooms.
One thing to keep in mind. Most grapes are self-fertile. A second vine may improve yield a bit, but it is usually optional rather than required.
To put that into practice: at a minimum, one self-fertile grape vine is usually enough for fruit. Better still, grow two grape varieties only if you want a broader harvest window, a backup vine, or a chance at slightly better fruit set in mixed plantings. If a grape vine is cropping lightly, fix pruning, sunlight, and winter cane damage before assuming it needs a pollination partner.
