How To Make Your Own Seaweed Fertilizer For Growing Potatoes

If you love tasty new potatoes as much as I do you’d probably do nearly anything to improve their taste and yield. That’s why you owe it to yourself to try using seaweed fertilizer to grow bigger and tastier potatoes this year.

Is seaweed fertilizer good for growing potatoes?

Yes, seaweed fertilizer provides potatoes with an excellent source of nutrients and growth stimulators.  According to Epic Gardening, seaweed contains over 60 micronutrients many of which are beneficial for potato growth. The additional presence of the growth hormones gibberellin, cytokinin and auxin is even better news for your potatoes. These hormones are bio-stimulants that boost plant growth and increase fruit yield.

How to make your own seaweed fertilizer for growing potatoes at home.


There are several ways to make seaweed fertilizer, depending on how much you need, and how you intend to use it. The three most common ways to use seaweed as a fertilizer in the garden are:

Composted Seaweed:

To make composted seaweed you will need a compost bin or compost pile. Here’s what you need to do.

  1. Harvest fresh seaweed.
  2. Rinse the seaweed to remove excess salt, if desired.
  3. Chop the seaweed into manageable pieces.
  4. Add the seaweed to your compost bin or compost pile. Fresh seaweed counts as green material in the compost pile and must be layered with brown or dry material, such as dried leaves or other browns from the yard.
  5. Compost the seaweed as part of your regular garden compost following your regular procedure.
  6. Apply the composted seaweed around plants as a mulch or work it into the soil as a soil amendment.

Dried Seaweed Powder:

Making a powder from dried seaweed will give you a convenient source of seaweed fertilizer for your potatoes, but it can be a bit of a challenge to make. Here’s how:

  1. Harvest fresh seaweed.
  2. Rinse it to remove salt and other residues.
  3. Hang the seaweed in the sun or spread it over a screen to allow it to dry.
  4. Crush or pulverize the dried seaweed when it is dry and brittle. If you are processing a small batch of dried seaweed fertilizer, you can use your food processor or blender to pulverize it. Other alternatives include using a heavy rolling pin to roll the dried seaweed, manually breaking up the seaweed by hand or using a mortar and pestle to grind the seaweed.
  5. Use the powder by working it into the soil as you would any powdered fertilizer.

Liquid Seaweed Fertilizer:

Many prefer to make liquid fertilizer from seaweed. Also referred to as seaweed tea, liquid fertilizer is quick and easy to make, but beware. Making liquid fertilizer from fresh seaweed can be smelly. Here’s what you need to do:

  1. Harvest fresh seaweed.
  2. Rinse the seaweed in a large colander to remove excess salt and any debris.
  3. Fill a large bucket or barrel with water.
  4. Add the fresh seaweed to the water and stir well. The seaweed should be covered with water.
  5. Cover the container and allow the seaweed to steep for 24 to 48 hours. While some prefer a longer steeping time, this mixture will get smellier the longer it sits.
  6. Dilute the liquid fertilizer with water at a 3 to 1 ratio with three parts water to one part liquid seaweed fertilizer.
  7. Apply to the soil around the base of your potatoes.


Fresh Seaweed:

Seaweed does not need to be processed before using it in your garden. It can be used fresh as it will break down naturally adding the nutrients to the soil. Here are some ways to use fresh seaweed to enhance the growth of your potatoes.

seaweed washed up on the beach
Seaweed washed up on the beach makes great fertilizer


Add fresh seaweed before planting.

This method gives your potatoes a good start and provides a boost of nutrients as they grow, too. Here’s how:

  1. Dig a trench to a depth of 6 to 8 inches for planting your potatoes.
  2. Line the bottom of the trench with several inches of fresh seaweed.
  3. Cover the fresh seaweed with 2 to 4 inches of compost or fresh soil.
  4. Plant your potatoes on top of the seaweed and compost.
  5. Cover the potatoes with fresh soil and firm it down with your hands to settle the potatoes and remove air pockets.
  6. Water your potatoes.

Use Fresh Seaweed as Mulch.

Fresh seaweed can also be used at any time as a mulch around your potatoes by covering the soil at the base of your potatoes with a layer of fresh seaweed. The seaweed will work to maintain moisture and suppress weeds while releasing nutrients to the soil below giving your potatoes a boost of nutrients.


Where do I get the seaweed from?

Seaweed should be harvested after it has washed ashore and can often be found after the high tide. Living seaweed should not be harvested as removing it may endanger the ecosystem. Although seaweed is free for the taking in many areas, check with local ordinances to make sure it is legal in your area.

How much seaweed fertilizer should I apply?

Because there is little danger of over-fertilizing your potatoes with seaweed fertilizer, how much you use depends on the growth and health of your plants. While an initial application of 3 to 4 inches of fresh seaweed to the planting trench will get your potatoes off to a good start, they may benefit from a dose of liquid fertilizer every 2 to 3 weeks. Fresh Seaweed mulch can be applied as thick as you want, but a 2-to-3-inch layer is typically sufficient.

How often should I apply it?

Apply liquid seaweed fertilizer whenever your potatoes show signs of slowed growth, generally once every 2 to 3 weeks.

Do you need to rinse the salt off seaweed before using it in the garden?

Opinions vary about the need to rinse away excess salt on fresh seaweed. Some sources claim that the amount of salt seaweed introduces to the garden is minimal and causes no problems. Others express concerns over adding salt to the garden soil.

Whether you rinse your fresh seaweed to remove excess salt before using it is up to you. I personally would rather err on the side of caution and rinse away the salt than risk future issues from salt buildup in my soil. How about you?