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How to: use seaweed

Photo - AlisonDale

Seaweed is a versatile natural resource that does great work in the garden.  

We use it on a fortnightly basis to keep plants healthy. 


Click-on hose applicators make it easy to foliar-feed plants with seaweed and douse the soil at the same time, though we do try to avoid watering the paths as the seaweed can encourage unwanted as well as wanted growth. Here’s are eight reasons we use seaweed in the garden:


1. Seaweed strengthens the cell walls of plants and so reduces frost damage and insect attack.

2. Seaweed contains plant growth hormones, such as gibberellins, which help seeds to germinate.

3. These same plant hormones help to reduce transplant shock, so it is useful to immerse a plant in seaweed solution before planting or replanting.

4. Plant hormones in seaweed help to increase the strike rate in cuttings.

5. Seaweed contains betains, which help with growth and increase yields in vegetable production.

6. Cytokinins are natural plant hormones found in seaweed that increase the sugar levels in plants, resulting in sweeter fruit.

7. Seaweed contains mannitol and alginic acid, which help to increase the acidity in soils, enabling plants, especially camellias and azaleas, to absorb the nutrients they need.

8. Seaweed improves the nutrient quality in vegetable crops, especially iodine and selenium.


Liquid Seaweed

Nurseries stock an ever-increasing range of seaweed solutions. Dilute according to the instructions on the pack, taking particular care with seedlings, ferns and palms. Liquid seaweed is often referred to as seaweed fertiliser but technically it is a plant conditioner as it contains virtually no nitrogen or phosphorus. It can, therefore, be used year-round, on all plants, and will not interfere with other nutritional input programmes.

Try: Seasol or Maxicrop. Combine Seasol and PowerFeed together for a good liquid feed; just make sure you use the mixture within 24 hours.


Dry Seaweed

Dried seaweed products may include seaweed meal, which is crushed and dried fresh seaweed; powdered seaweed extract, which is produced by boiling the seaweed and evaporating off its liquid content, leaving a concentrated solid extract that is then powdered; or liquid seaweed extract, which is produced from fresh seaweed by water extraction. Dry seaweed is great for adding to compost heaps or mixing into your own solution.

Try: Eco-cweed, a powdered seaweed concentrate. It is harvested sustainably from the oceans off Nova Scotia.


Enriched Seaweed

Fortified seaweed extracts (usually liquid) contain added elements, such as nitrogen, phosphorus and potassium and quote an NPK ratio on the product label. By adding blended fish they provide even more nutrients and a growth boost for your plants, negating the need for other fertilisers.

Try: Amgrow’s Harvest or Yates Uplift Plant Starter & Root Booster. Both have seaweed and fulvic acid that result in stronger, healthier roots leading to bigger, more productive plants. Use on seedlings, transplanted plants, new plantings and new lawns, until established.



You can collect your own seaweed from  beaches, as long as you check with local councils first. If you do have access to fresh seaweed, wash off the seawater then spread it over the soil as a mulch, add it to the compost heap, or use it to make your own seaweed tea by soaking seaweed in buckets of water.


For best results in your garden use seaweed fortnightly. It can be applied all year round – in the dead of winter and the height of summer!

Text: Linda Ross


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Author: Linda Ross