Answer: I share your frustration, but I don't think there is a single source of reference for all of the plants we grow in our gardens. If you understand how plant foods work, you can choose the correct fertilizer for your plants. Here, in a nutshell, is what you should be looking for in plant food:
You'll find 3 numbers on a fertilizer package. They indicate the amount of nitrogen, phosphorous and potassium (in that order) contained in the formula. Nitrogen promotes lush green growth; phosphorous promotes stem strength and encourages flowering; potassium helps roots grow and works in conjunction with phosphorous to strengthen stems. So, if you're growing non-flowering plants such as ferns or lettuce or cabbages, you'd want a high first number, low middle number, and a high last number because you don't want to promote flowering. 10-5-10 for instance. If you're growing a flowering plant (perennials and shrubs), you'll want a lower first number and a higher second and third number. 10-20-20 is a good example. And, if you're growing root vegetables such as carrots, you'll want a higher third number 5-5-10 for instance.
Most general purpose fertilizers will make all of your perennials, shrubs, bulbs and daylilies happy but if you want to custom mix your own formula you can purchase separate packages of nitrogen, phosphorous and potassium.
Hope this helps solve your fertilizer problem!
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