The uses of seaweed as a supplement

The uses of seaweed as a supplement
Luke Sumpter

Want to know how your cannabis plants can reap the benefits that seaweed has to offer? Click to find out how it helps plants and how to collect seaweed.

Seaweed contains all of the major and the minor plant nutrients and all trace elements, such as alginic acid, auxins, gibberellins and antibiotics. This is true for all forms of seaweed available; fresh seaweed, seaweed meal and liquid seaweed extract. Fresh and ground up into meal, seaweed however also contains vitamins A and C, B12 and K and E group vitamins as well.

The liquid extracts do not contain these vitamins though. The seaweed, when applied will start to decompose in about a week. The decomposition process of the seaweed breaking down will at first remove some nitrogen from your soil, but will replace and ultimately greatly increase the nitrogen levels.


Seaweed keeps the soil moist at a ground level and saves you water, and the effort of having to water your plants more often. It repels slugs, pests and does not contain foreign weed seeds, and we are not talking about cannabis, we mean the weeds, that you don’t want, such as horsetail, that can be a real pain to eradicate from your garden.

Seaweed also eliminates the need to weed out, because it covers the soil and blocks the new weeds from sprouting. Keep this in mind when applying seaweed to your germinating cannabis plants. Do not smother them with seaweed, making it impossible for them to grow out of the soil when still germinating.

Seaweed also boosts the metabolism of your plants, either when it is added to the soil or if it is applied as a foliar spray.

It enriches the soil with trace elements and lightens the soil by changing its structure to a more crumb texture. This lighter texture makes it easier for the plant to form roots and find the nutrients it needs.


When gathering seaweed, look for the middle of the beach, as the seaweed is dryer and contains fewer bugs. Bear in mind to only take a third of all the seaweed available at one spot and move on to other patches. This makes sure, that there is still enough seaweed left for the local wildlife to replenish what you’ve taken over time.

Look for fine, broken up seaweed, for this is easier to gather than the large clumps, that often are very heavy and slimy. The easiest way to transport the just gathered seaweed is in plastic onion bags, the holes will let the seaweed to drain it’s water and it is easy to hold, even with slippery hands.


Apply the gathered seaweed to the soil quickly after collecting it from the beach, because it will start to decompose, leaving a clear space between the stems of the plant. Repeat the process of applying the seaweed to the soil after a week, because most of the seaweed will have shrunk and started to decompose.

If you are worried about salts entering your grow and affecting your soil, the seaweed can be hosed down on the driveway or in the garden prior to applying it to your soil.

Luke Sumpter
Luke Sumpter

Luke has worked as a cannabis journalist and health science researcher for the past seven years. Over this time, he’s developed an advanced understanding of endocannabinoid system science, cannabis phytochemistry, and cultivation techniques.