Difference Between Fish Fertiliser and Seaweed Extract


Walking down the aisle of tonics, brews and potions of any nursery can be overwhelming. We get it! Trying to figure out whether to use the Eye of Newt or the Toe of Frog for a flourishing garden is confusing. Save that boiling cauldron for a pot of tea, we are here to help demystify two common allies in the garden.

The words fish fertiliser (emulsion) and seaweed extract are thrown around a lot by gardeners, so much so people often think they are one and the same. Although they are both your friend in the patch, fish fertiliser and seaweed extract have slightly different applications and work best being used together, rather than instead of the other in your veggie patch.

Fish fertiliser, or fish emulsion, is a fast-acting, concentrated liquid fertiliser. The beauty of it is that it is made from by-products of the fishing industry and is a particularly useful application for getting rid of non-native invasive species… Looking at you, Carp. It’s an excellent source of nitrogen and helps promote good microbial growth within the soil. That strong smell that stings the nostrils if you take too close a whiff? That can also sting the nostrils of your plant. When applying it in your patch make sure you dilute it with water - typically at a ration of 1:100 - that way there is little risk to burning plants. It is also advisable to water liberally post application.

Seaweed extract on the other hand may smell like it is cut from the same cloth as fish emulsion, but it isn’t. Seaweed has complex carbohydrates that stimulate microbes in the soil and assist plants with eating all their nutrients… here comes the aeroplane. Usually made from kelp, and so plant-based, it is full of plant hormones like auxins, cytokinins, betaines, and gibberellins. This makes it great for helping prevent transplant shock. Seaweed also helps to improve the thickness of plant cell walls. This aids your plants in protecting them against attacks from pests and disease. Available as a powder or a liquid concentrate, seaweed extract is easily applied to your garden when diluted with water. Again don’t drink the cordial straight, make sure you dilute it for everyone’s health.

The key differences are that fish fertiliser/emulsion is high in nitrogen, which is key for plants as it is a major ingredient of chlorophyll, the compound that plants use  to photosynthesise (use the suns energy to produce sugars from water and carbon dioxide). Seaweed on the other hand is all about the growth hormones. It helps with transplant shock, promotes root development and strengthens the cell walls of your plants, making it more resistant to colder weather and pests. Used together this dynamic duo are unbeatable in the veggie patch! No pair can compare, not even Mulder and Scully or Bert and Ernie. So carpe diem, or should that be carpe carp? Seize the power of fish emulsion and seaweed extract in your garden.