It depends on what you're growing. If you want to grow organically, you will add quality compost and a little bit of nitrogen fertilizer. You don't need to add other things. If you're looking for a fertilizer that does everything, you want a balanced fertilizer. If you look at the front of the bag of fertilizer, there are three letters, NPK, representing nitrogen, phosphorus, and potassium, along with their quantities, for example, 10-10-10 or 20-20-20. This is much more potent and a lot easier to over-apply. You have to be very careful. An organic fertilizer might look like 3-3-3 or 3-5-2. It's generally weaker and you have to generally apply more of it. What you apply is based on the requirements of your plants. Some plants want more fertilizer than others.