What type of fertilizer /product/substance will help my flowering plants to actually flower abundantly?

Hi, I live in WI. and try to plant flowering plants that are for my planting zone.Generally the majority of these plants will do good EX:roses, hollyhocks,hydrangea etc... but many fail to flower or only get a few flowers on them. I do try to enrich my soil with my own compost and learned from an old wise gardener how to make my own liquid compost. Now this same gardener told me that if I select a product from the store that has the numbers on the side ex:10 10 10 -JUST AN EXAMPLE-that the middle number should be the highest for good flowering. Ex: 10-20-10 Feedback please. I also do try to enrich my soil, water according to that plants needs, consider sun needed, and use mulch. Funny part about this is that often I will throw trimming in my field and the next yr. I find them growing. Ya no care, no water, no weeding, fertilizer etc...KInd of funny. Thanks so Much FYI-I really do prefer a natural enhancer like compost. My neighbor man told me each day he would pour his old coffee from his mug that he kept in the car on plants that nevered flowered and they did really well. Ya a single guy who also would pour his unfinished beer on the plants and they were just beautiful. Tons of flowers. Of course he said he had no clue they were even flowering plants. Said his mom felt bad he had no plants so she kindly put them in