Organic fertilizer is a must for every kind of vegetable and fruit. If you wish to have a better yield of your vegetables or fruits, you must use organic fertilizer. I have been growing strawberries for almost ten years, and using organic fertilizer has always been a crucial part of growing strawberries. Strawberries always demand three types of nutrients: potassium, phosphorus, and nitrogen. Potassium helps to maximize fruit quality and taste, and phosphorus provides great help in improving plant energy management. So I will suggest some organic fertilizers that can supply those nutrients. Organic fertilizers that can provide those nutrients are blood meal, soy meal, fish meal, and compost tea. You can also use tomato feed; although tomato and strawberry are different plants, they require similar nutrients, so using tomato feed is not a bad idea at all. Now, if you ask me what you should use for container strawberries, John Innes No. 3 compost has always been my favorite for the last few years. Although you can also use other fertilizers, if you ask for my personal advice, I would say you should use John Innes No. 3 compost because it is best for containers.