When do you fertilize
I am no pro, but I think that you have to be quite careful with commercial fertilizers on tiny leaves. I "side-dressed" my asparagus bed , rhubarb and roses last week, and "top-dressed" with a 10-10-10 the bare patches on the lawn that I had seeded and put soil on. Then I watered everything...and then, of course, it rained...I am a zone 6a, if that helps.
For fruit trees, BTW, its fertizer spikes in the fall after pruning.
"Organic" as in compost? Compost you can spread any time. I usually spread some in April, right now, and some in the fall if I have a good pile.
If you're referring to "organic" fertilizers that are in, say, liquid or granule form, these are fast acting and need to put on when they're needed. I think you're in zone 3, so right now is a good time to fertilize with these products.
But _what_ are you fertilizing? Some things need more fertilizer than other things.