Depends if your spaying for micro nutrients or general nutrition. All commercial growers use low biuret Urea, which they apply 3 times a year. 2-months prior to bloom, after early drop, and again in July. The first application increases the bloom, second increases the amount of fruit held by the tree, and the third spray increases the size of the fruit. There are various micro nutrient sprays available. I use one called STEM, but I'm not 100% sure it is on the market,