What should I add to the soil to be sure plants will have enough nutrients?

Question: I planted a new flower garden last summer (2020). I dug up and removed the old sandy soil and put about 5″ of a soil and compost mixture down. I planted all new plants in this area. The plants thrived last summer and fall season. I am wondering what I need to add to read more What should I add to the soil to be sure plants will have enough nutrients?