A Guide to Using Seaweed in the Garden

Using seaweed in the garden is an effective way of boosting the health of your plants by harnessing the power of this versatile resource from the sea

seaweed mulch

Seaweed is a nutrient-rich and versatile plant which has a number of wonderful benefits when used around the garden. It has long been used to promote healthier crops thanks to its high levels of nutrients and trace elements, and its gelatinous texture means it breaks down quickly, delivering its benefits quickly where they are needed. Seaweed can be used in a number of different ways around the garden, depending on your needs.

 Gathering seaweed

 Seaweed is a wonderful, natural and free resource. Start by gathering it from your local beach, ensuring it is fresh and healthy looking. Also make sure it is legal to gather seaweed and that you don’t over-harvest the area. Instead, pick no more than around a third of the seaweed in each patch. Using scissors or a knife to cut away the seaweed you need helps to keep the plant’s roots in tact, helping it to regrow more quickly. Pick seaweed from the middle of the beach where it will be clean, moist and free of insects, but not dripping wet. Gather in a sturdy woven sack or jute bag and use promptly, before it dries out.

 Making fertilizer

 One of the most effective ways of harnessing the power of seaweed in your garden is with a home made seaweed fertilizer.

  • Rinse any sand, salt and other debris from your freshly gathered seaweed.

  • Fill up a bucket with water, around ¾ of the way full. Add your seaweed up to the waterline and stir well before covering with a lid or tray.

  • Leave the seaweed for at least 8 weeks, stirring every 3-4 days. You may wish to keep the bucket outside, or in a garage or shed to stop the smell disrupting your everyday life.

  • If you wish, you can strengthen the fertilizer by adding a little fish emulsion. This makes the fertilizer more well-rounded by providing phosphate and nitrogen, alongside the seaweed’s potassium.

  • Strain the liquid into a bottle or jar, giving the seaweed pulp a good squeeze to capture all the fertilizer. The seaweed can be topped up with more water to make another batch of fertilizer. After a second use, the nutrients will be exhausted, so simply dispose of the old seaweed by adding it to your compost heap.

  • Dilute with 6 parts water to every 1 part fertilizer and use around the base of your plants to boost their health and growth rate.

 Mixing seaweed with compost

 Alginic acid in seaweed helps compost to break down more quickly, as well as allowing it to take up the many nutrients that seaweed contains. But it’s still important to be careful when mixing it into your compost heap. Seaweed poses a risk of choking your compost, causing the process to take place anaerobically, which generates bad smells and impacts on the compost’s quality. Mixing in materials like leaves and straw, which are high in carbon, helps to improve airflow around the compost, preventing this from taking place. Shredding up your seaweed into smaller pieces can also help it to mix more evenly into the compost, again preventing it from choking parts of the compost. Once well mixed, allow to break down as normal before using around the garden.

 Using seaweed as mulch

 The cool, moist, gelatinous properties of seaweed such as kelp lend themselves well to use as mulch during hot, dry conditions. Gathered seaweed should be applied within around 36 hours to prevent it from breaking down and turning slimy. The seaweed should be applied generously- around 4 to 6 inches in depth, avoiding the plant stems, as it will soon start to shrink as it dries. After a week of initial application, add a further layer of seaweed to keep the soil covered. This should now act as an effective mulch for a number of weeks and work to maintain soil moisture, improve texture, suppress weeds and repel insects. Seaweed can also be mixed with other varieties of mulch such as leaves, newspapers, bark or grass cuttings to make it go further.

 Why is using seaweed in the garden so effective?

 Seaweed’s high nutrient content, coupled with its inclusion of trace elements makes it an effective, broad spectrum fertilizer. These trace elements, coupled with hormones and carbohydrates, stimulate more rapid plant growth. Seaweed also has the added benefit of being free of diseases which can harm land-growing plants, so there is less risk involved in using it in compost or as mulch than with bark or grass cuttings.

Image sourced: Rob n Rae Cornelius

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