Toggle navigation

How to use seaweed in the garden

In their new book ‘Milkwood’, permaculture gardeners Kirsten Bradley and Nick Ritar devote a whole chapter to the glories of seaweed.

Beyond its uses in the kitchen, seaweed is great in the garden.




Try this:

Seaweed can be a fantastic resource for fertilising your garden. There are lots of easy ways to use it to increase the health of your soil, as well as your vegies and flowers. Seaweed contains useful amounts of iodine, copper, iron, potassium, manganese, phosphorus and zinc. There’s no need to wash it or dry it before use in the garden. You can use it as a mulch, add it to your compost or brew it into a seaweed tea. Whatever form you use, seaweed is a great soil conditioner that helps to build a healthy soil food web in your garden. Some of the benefits of using it as a mulch include:


  • It's an instant, broad-spectrum, slow-release organic fertiliser - lay it down and you're done!

  • As a top layer mulch it becomes dry, crinkly and spiky, and is helpful for deterring snails, slugs and some household pets.

  • As a faster-decomposing layer under another mulch, it’s also great for slug control, as the slugs dislike the small amount of salt.

  • Seaweed is weed-free - unlike many straw mulches, there are no embedded weed seeds - and it doesn’t blow away in the wind like some mulches can.

  • In some sandy soils, the alginates in the seaweed (particularly bladder wracks) can really help an as additional wetting agent.

Collecting tips

  • Only forage from somewhere that’s relatively clean and non-toxic - avoid ocean outfalls and polluted waterways.

  • Check the regulations where you're going before you head off.

  • Stick to gathering seaweed well below the high tide mark - the seaweed at or above the high-tide mark is generally colonised with all manner of critters and performs important biosphere functions. Stick to the fresh stuff.

  • Forage lightly and mindfully - if we want vibrant ecosystems, it’s up to all of us to take only our share.

For more tips on using seaweed in the garden and in the kitchen, check out Milkwood: Real skills for down-to-earth living by Kirsten Bradley and Nick Ritar, published by Murdoch Books, from which this is an edited extract. And listen to our podcast chat between Linda and Nick here.