Some organic fertilizers that are great for broccoli plants are as follows;

Compost: This provides a balanced source of nutrients and helps to improve the structure of the soil.

Fish emulsion :This is a good source of nitrogen, which is essential for broccoli plants.

Seaweed fertilizer: This contains potassium and other minerals that are important for plant growth.

Worm castings are a great source of beneficial microorganisms that help to improve soil health and the uptake of nutrients by plants.

In addition to the fertilizer application, also ensure to choose a fertilizer that is formulated for vegetables.

Ensure to follow the instructions on the label, as over-fertilizing can damage the plants.

Also ensure to apply fertilizer when the soil is moist, as this will help the plants to absorb the nutrients more effectively.