The first few years I was gardening, I fed my plants with mixes I bought. I was diligent about buying the right mix for the right plant. African violet food, rose food, food for annuals and food specifically for perennials. Some were liquid you mixed and watered with, some were granular for mixing into water and some were granular for mixing into the soil. Slow release. I spent a small fortune in the two years it took me to realize that the same three nutrients are required by all plants and the balance of them in the plant food really didn't matter that much.
Plant nutrition can be really complicated. There are micro vs. macro nutrients, essential vs. beneficial elements, and soil pH. This can be further complicated by soil pH, in that if the pH is less
than 4, the phosphorus will be chemically locked in the soil which makes
it unavailable to the plant. Thankfully, I have found it can be simplified. What we need to remember as gardeners is that the plant uses nitrogen for stem and leaf growth, phosphorus for flower and fruit growth and potassium for roots. So if you are feeding flowers, you want a higher phosphorus number and if you are feeding root crops, you want a higher potassium number.
Over the long haul, I have discovered that making my own compost solves every problem I have had in the garden. If you use a good balance of different things in your compost, you end up with a good balance of nutrients in your soil. The trick is to keep the compost material diverse. When I first started composting, I had trouble keeping it free flowing and easy to stir. Everything I added, it seemed, was wet and heavy. That too, is easily solved. Keep your compost a good balance of wet and dry material and you will find success. I use a layer of green (wet) and a layer of brown (dry) material and just continue to build and stir, always leaving a dry top layer.
A few other tips: keep the top layer a dry layer to eliminate smells coming from the compost, grass clippings can be green or brown depending on the level of moisture in them, do not compost meat or bones if you do not want insects or smells but all waste vegetable material are excellent additions. If you have never composted, do not let the complications scare you. Just try it. A good compost pile does not smell and produces black gold for your garden that has no chemical substitute that will perform as well. If you are just getting started,
Organic Gardening has
a good, brief video to help you select your compost ingredients. I encourage you to jump right in and try it. I know I was sorry I waited so long once I spread the first results in my garden soil and witnessed the difference good compost can make. Much better than buying something in a bottle and environmentally friendly too - no chemicals and less landfill. Happy composting!