I have never had one but there were plenty about in Belgium and they were always pruned in winter when the structure could be seen. Training in of new shoots was done in summer when the wood was flexible..
I assume they pruned back outward facing shoots that couldn't or wouldn't be trained in to the structure. As with wall trained shrubs, cutting back to just two buds would encourage lateral growths to thicken the top and you'd need to make sure the trunks were clear of shoots so growth is concentrated up top.
I take a hedge cutter to mine once the main flush of growth is completed to cut the face to a "hedge" surface, and create a "box" shape. But its quite a while since I planted it and the grow is strong now. I initially created a layered structure tying in young branches along the supports (I've just got horizontals end-to-end of the Pleach, rather than grid-canes that pre-formed plants tend to come with)
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I have never had one but there were plenty about in Belgium and they were always pruned in winter when the structure could be seen. Training in of new shoots was done in summer when the wood was flexible..
I assume they pruned back outward facing shoots that couldn't or wouldn't be trained in to the structure. As with wall trained shrubs, cutting back to just two buds would encourage lateral growths to thicken the top and you'd need to make sure the trunks were clear of shoots so growth is concentrated up top.
The RHS offers this advice - https://www.rhs.org.uk/advice/profile?pid=155
I take a hedge cutter to mine once the main flush of growth is completed to cut the face to a "hedge" surface, and create a "box" shape. But its quite a while since I planted it and the grow is strong now. I initially created a layered structure tying in young branches along the supports (I've just got horizontals end-to-end of the Pleach, rather than grid-canes that pre-formed plants tend to come with)