The best fertilizer for Broccoli contains high amounts of phosphorus and low amounts of nitrogen. It is crucial to have your soil tested and apply phosphorus and potassium according to the recommendations. Broccoli is a heavy feeder and requires fertilizers throughout the growing season. These options include Vermiculite, organic fertilizers, seaweed or fish meal, and compost. Avoid using fertilizers with weed killers. Additionally, watering broccoli plants properly is crucial. Finally, side-dress broccoli plants with compost at midseason and give them a nitrogen boost after three weeks of growth.