Some of mine are 5 feet apart . The distance only only limits how they can spread. I tried ( we’ll see how it works out) alternating scaffold height for those next to each other. One tree got the first and third wire and the other got the second an fourth. This allows the scaffolds to spread and if I like one variety more than the other I have a ready made base for grafting.
Raintree has a nice selection of pre-made multi-graft espaliers for both apples and pears. Check them out for guidance as to varieties.
Stark has non-espalier multi grafts you can use for variety check.
Well, I’m not from zone 5/6 but I have two apple espalier trees planted very close, probably only 4ft.
I did the same thing as Mike described, one got first and third wire and the other got the 2nd and 4th wire. They are trained on a wooden fence and my neighbor on the other side of the fence has another apple tree just another 6-7 ft away from one of my espalier tree.
My trees are on M111 rootstocks and vigor seems normal so far (9 years).
I believe adding a third one should be fine too. Isn’t this similar in concept as Belgium Fence?
Sorry, I’m not knowledgeable to comment on types for your region. I am not happy with what I picked for my espalier and in fact I have tried to top work part of one of them 2 years ago with different varieties, making stupid decisions along the way.
Seeing Mike’s Zestar espalier yesterday made me so envious.
In our climate, other than selecting varieties that that we like to eat, and that they are spur bearing, we also have lower chill requirement as a constraint.
I have 2 espalier apple trees, Hudson’s Golden Gem and Fuji, still in the work for the past 4 years with plenty of mistakes. Spacing is 6’ apart and 1’ away from the fence. According to Alan (Harvestman), the Hudson’s GM is a sparingly fruit bearer for him so you probably should steer clear.