1) the tiny growing season due our latitude! Reponse, we put in a polytunnel, with a heat sink, to try and extend it a bit. We start our tomato and similar, indoors, in January to give them a bit of an advantage.
2) the shifting Gulf stream - never noticed it down south (it either rained or it didn't) - has an enormous effect up here. The last couple of summers have disappeared behind gail force winds (I'm talking 60mph+ on a nearly daily basis) and horizontal rains that nearly slice you in two. Some days we literally didn't leave the house. Response, we have several cold frames and cloches to protect outdoor crops .
3) Livestock - not of the sheep or cow variety but snails! Huge, hungry snails that strip a garden overnight. When we moved up here we scoffed at the regular use of slug pellets (we're organic dontcha know) but I confess that this year, in desperation, we've resorted to the same.
And to Tomorite! We've carefully gathered seaweed and comfrey and nettles, in previous years, and made wonderful teas that just don't seem up to the task of giving our crops the advantage they need over all the other growing conditions.
We really need a decent crop this year. Not just to boost our flagging confidence but also to get back something from the huge investment (financial and personal) we've made in this polytunnel etc. I'm hoping that once we've got to know it better we'll be able to revert to (for us) a more comfortable gardening style. But in the meantime any advice that may help us get there would be welcome.
Ah, confession is a wonderful thing

Edit: I forgot to mention that we've started the windbreaks by building fences and growing willow but it'll take a few years for it to get to a reasonable height and thickness.