|Geneva 16. Photo from HERE.|
All of the rootstock, B9 and above in the listing NEED support.
All rootstock G.202 and below BENEFIT from support. Supporting the trees reduces the risk of the graft union snapping on windy sites. It also induces precocious fruit bearing as carbohydrates are not "suck" into growing a beefier trunk.
All of the Geneva rootstock are cold hardy, fireblight resistant and collar rot resistant.