Thanks for the birthday wishes yesterday!

I have a question today on fertilizer. I think I should be fertilizing my flowers, but not sure how to go about it and what to use. I used some Osmocote when planting a few shrubs this spring and it says 'will feed up to 3 months' and with living in ND, 3 months is about as long as our summer is, meaning I only have to fertilize once? I don't think so. I have watched commercials on that Spray-N-Grow - does it work? I have seen tags on plants I have purchased saying to fertilize every 1 to 2 weeks.

Okay - what's a happy medium? I feel like I need to put something on everything.