oh. i just composed the following post before i noticed that the date of your original post was some time ago. this probably isn't too helpful and you have probably already made your decision. How did it turn out? did you decide to do north south trellises?

my original response:

it likely depends on how much total sun your garden plot gets in the summer months when these plants will be growing. then you can just put up a trellis or a pole the right height and see if the morning or afternoon shade will reduce the next door beds hours of light too much.

I am less far north than you but I am experimenting with north south rows that have trellises. the reason i decided that this would work for me is that my plot gets something like 14 hours of sunshine in the summer... and we have lots of 95 degree plus days here in northern utah. so a little shade probably won't hurt.

it also allows me to attempt to plant crops that are less heat tolerant (like potatoes) between the trellised crops with the hope that they will do better than if they were scorched through the summer.

i have 8 16' x 3.5' beds with paths between and am trellising in 3 of them: pole beans, tomatoes and squash/cukes/melons.

jon