Look at the ingredients listed on a bottle of tomato fertiliser; seaweed is there. Using whole seaweed, instead of a liquid extract from a bottle, doesn’t offer standardised dosage of nitrogen, potassium and magnesium, but it brings the added bonus of improving soil condition by adding organic material to its structure as well as nutrients. There is also some evidence that mulching with seaweed reduces the spread of blight on potatoes and tomatoes.
Spring storms often leave a generous supply of fresh seaweed along the tideline or free floating in the sea. Collecting seaweed from rocks exposed at low tide, use a pair of scissors to cut sections off while leaving most of each individual still attached by its holdfast. If duck-diving down to kelp beds underwater, cut lengths from the ends of kelp blades, leaving stipe and holdfast intact to continue growing. Underwater a diver’s knife is easier to use than scissors.
Grab some free fertiliser!