My first concern in zone 3 would be winter hardiness. So if you do decide to fertigate don't apply any after June. You don't want to stimulate late growth that might get frozen. That doesn't leave much time to use your system. So why not apply any needed fertilizer in May or June by broadcasting around the trees?

If you have decent soil your trees shouldn't need much fertilizer in that climate.

Thanks for your comment. I live on the shore of Lake Superior so its a bit warmer here. The soil is 4 feet of rock and sand then bedrock so irrigation is needed daily. The main reasons for building an orchard system is to protect the house from a forest fire, and i love honeycrisp apples. I fertilized in mid july last year and had green leaves on some of the trees until january. The buds are starting to open now so i think they survived the winter.
I just got my soil results back today, p 100+ and k 274 ph at 6.9. Hmmm, seems easier to just run from the forest fires.