I need to construct a pair of wire trellis for my dwarf apples and for my bramble berries.
First, what is the benefit of putting the wires under tension? I’ve seen some kits and some trellis that use a tension device (on a hook that sinks in the ground, usually) at each end, but what is the overall benefit vs just attaching the wire to a fastener?
Second, I’m thinking of running crosspieces on top of the bramble berry trellis and training a grape vine across them, either 3, 4, or 5 lines. I’m unsure if this is going to cause a shade problem for the brambles, though. The berry bed also has gooseberries and currants in it, but they pretty desperately need some shade here in 7a so I’m not real worried about them.