DIY Seaweed Fertilizer: Making Fertilizer Out Of Seaweed

DIY Seaweed Fertilizer: Making Fertilizer Out Of Seaweed

By: Darcy Larum, Landscape Designer

Throughout history gardeners in coastal regions have recognized the benefits of the slimy green “gold” that washes up along the shore. The algae and kelp which can litter sandy beaches after a high tide can be a nuisance to beach-goers or workers as the common name “seaweed” implies. However, after using seaweed in the garden, you may see it more as a miraculous gift from Poseidon than a nuisance. To learn how to make seaweed fertilizer, read more.

Using Seaweed as Fertilizer for Plants

There are many benefits to using seaweed in the garden, and many different ways to use it. Like most organic material, seaweed improves soil structure, increasing soil porosity while also improving moisture retention.

Nutrients in the seaweed also stimulate beneficial soil bacteria, creating rich, healthy soil for flowerbeds or edible gardens. For this purpose, dried seaweed is tilled or turned directly into the garden’s soil. Dried seaweed can also be put into compost piles, adding a power punch of nutrients.

In some regions, shorelines are protected areas, including the seaweed. Collecting from some beaches is often prohibited. Do your homework before collecting seaweed from beaches to avoid penalty. In areas where seaweed is free for the taking, experts suggest collecting only fresh plants and using a burlap or mesh bag to carry them. Only collect what you need, as extra seaweed can quickly become a slimy, smelly mess as it decomposes.

How to Make Seaweed Fertilizer

There is disagreement amongst gardeners about soaking or rinsing fresh seaweed to remove sea salt. Some experts suggest soaking the seaweed for about an hour and/or rinsing it. Other experts argue that the salt is minimal and rinsing removes valuable nutrients. Either way, fresh seaweed is generally dried before being tilled into garden, mixed into compost bins, laid as mulch, or made into DIY seaweed fertilizer tea or powder.

Once dried, seaweed can be used immediately in the garden or chopped up, mulched, or ground. DIY seaweed fertilizers can be made by simply grinding or pulverizing dried seaweed and sprinkling it around plants.

DIY seaweed fertilizer teas are made by soaking dried seaweed in a pail or barrel of water with a partially closed lid. Infuse the seaweed for several weeks then strain. Seaweed fertilizer tea can be watered in at the root zone or used as a foliar spray. The strained remains of the seaweed can be mixed into compost bins or gardens.

This article was last updated on

Read more about Soil, Fixes & Fertilizers

Is seaweed good for tomato plants?

A Seaweed Tonic However, a tonic that can be given to small tomato plants is organic liquid seaweed extract. This can be applied as a foliar spray, it is organic and helps give a boost to encourage lush green leaves. It also boosts the immune system of plants helping them to fight off disease.

Similarly, which plants like seaweed Fertiliser? Another benefit of using seaweed fertiliser over time is it acidifies and adds iron to the soil, which is great news if you are growing acid and iron hungry plants like gardenias, camellias, azaleas and rhododendrons. It's great on native plants as well.

Just so, is seaweed good for your vegetable garden?

Seaweed is a broad spectrum fertilizer that is rich in beneficial trace minerals and hormones that stimulate plant growth. Seaweed is high in carbohydrates which are essential building blocks in growing plants, and low in cellulose so it breaks down readily. Seaweed shares no diseases with land plants.

What is the best fertilizer to use on tomatoes?

If your soil is correctly balanced or high in nitrogen, you should use a fertilizer that is slightly lower in nitrogen and higher in phosphorus, such as a 5-10-5 or a 5-10-10 mixed fertilizer. If you are slightly lacking in nitrogen, use a balanced fertilizer like 8-8-8 or 10-10-10.

Seaweed as a Natural Fertilizer

Seaweed as an organic fertilizer has a lot going for it. It’s an abundant resource that washes up on beaches throughout the world. It can be dried for easier transport, or incorporated wet into compost. It’s also a good source of plant nutrients, such as nitrogen, phosphorus, potassium, calcium and magnesium.

Seaweed has a rough, fibrous texture, making it an effective soil conditioner. It improves soil drainage and aeration when added to compost or tilled directly into the soil. Seaweed has a neutral to slightly alkaline pH and can help neutralize acidic soil — a good thing for seaside gardens, which are often acidic.

Preparing Seaweed Fertilizer

Most beachcombers look for sea shells, but collecting seaweed instead not only provides a free source of fertilizer, but also cleans up beaches, making them more appealing for recreation. Take a few big buckets when you visit the beach to store the seaweed. Both brown and green types of seaweed are suitable for fertilizer. Ask the local parks and recreation office, though, before harvesting seaweed from a protected beach.

Spread the seaweed in a thin layer and wash it thoroughly with fresh water to remove salts, or spread it on a hard surface and allow summer rains to leach the salt out. Putting it in a rain barrel serves the same purpose. Do not use fresh seaweed without washing it! The salt in it will burn or kill your plants.

Using Seaweed Fertilizer

After the seaweed has been thoroughly cleaned, you can add it to a compost heap in either wet or dry form. Dry seaweed functions as a brown (carbon-rich) ingredient, similar to dead leaves or small twigs. Wet seaweed is a green (nitrogen-rich) ingredient. Mix seaweed with other organic materials to prevent it from matting together in a slimy mess in the compost bin.

Seaweed makes an effective mulch, as well. After it is clean, spread it on a hard surface and allow it to dry out in the sun. Use it to mulch flower beds, trees and shrubs, like you would wood chip mulch, or add it to vegetable gardens to suppress weeds. Use it to cover tender plants, such as strawberries, if frost threatens.

Other Seaweed Fertilizer Options

Of course, not everyone has a free, never-ending supply of seaweed right outside their door. If you’re interested in the benefits of seaweed fertilizer, but lack a nearby beach, consider dried seaweed products instead.

Kelp seaweed products come in several forms, including powders, liquids and enzymatically digested formulas. These fertilizers are used primarily for the micronutrients and growth hormones they provide. They are usually a poor source of nitrogen, phosphorus and potassium. They may be combined with dried fish fertilizers, which boost the amount of nitrogen they contain. Dried fish formulas often have an objectionable fish smell, but the odor soon dissipates.

Want to learn more about using seaweed as a natural fertilizer?

Check out these resources:
Caring for Plants: Using Seaweed from University of Florida
Organic Fertilizers [PDF] from Colorado State University

What is Seaweed Fertilizer?

Join the Community

Seaweed fertilizer is fertilizer which is derived from seaweed. Seaweed is rich in vitamins and minerals which can be beneficial to plants and it is a very balanced fertilizer product which can be safely applied to many different kinds of plants. Special formulations which have been developed for particular types of plants are also available.

People have been using seaweed as a crop fertilizer for a very long time. Historically, seaweed was spread directly onto the fields. The seaweed acted as a mulch, which was especially useful in areas where the soil was thin and of poor quality, as the seaweed prevented soil loss, and it also provided nutritional support to the plants. However, seaweed breaks down slowly, and modern seaweed fertilizer is usually made with processed seaweed, a departure from the days of applying seaweed directly to the garden.

Seaweed fertilizer is available in liquid and meal forms which can be spread on the garden. Foliar feeding sprays based on seaweed are also available. In addition, it can be included in combination fertilizer products and it is also sold in the form of concentrate. The precise balance of nutrients in seaweed fertilizer varies, depending on how it is processed and what is blended in with it, and the container should provide specific information about the contents.

One advantage to seaweed fertilizer is that it is often available in a completely natural form, a concern for some gardeners. It can also be found in certified organic fertilizer blends, for gardeners who are maintaining organic gardens. With the exception of concentrated seaweed fertilizer products, seaweed fertilizer is also unlikely to cause fertilizer burn, and gardeners do not have to worry about accidentally applying a little bit too much to their crops. This product also acts as a soil conditioner, enriching the soil and helping it retain its structure.

Most garden stores carry this product and can order it by special request if customers have specific needs. It is also possible to order it directly from companies which harvest seaweed and make seaweed fertilizer. Shipping fees can be costly when ordering this product, and people may want to ask about volume discounts or consider making a big order with a friend to make the shipping costs worth it. For special needs plants, it is advisable to purchase fertilizers specifically formulated for those plants, and gardeners should also remember to use tools like soil testing to find out how much fertilizer their soil needs.

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

How to Fertilize with Fish & Seaweed

Related Articles

If you want the biggest vegetables and prettiest flowers this season, then don't skimp on the plant food. Synthetic fertilizers get the job done, but accidentally overfeeding with them may spell disaster for some plants. Organic and natural fertilizers, such as fish and seaweed emulsion, are much gentler on plants. In general, such an emulsion contains 2 percent nitrogen, 3 percent phosphate and 1 percent soluble potash, plus other trace nutrients and minerals. Fish and seaweed emulsion works on all types of indoor and outdoor plants. Shake the emulsion's bottle well, and dilute the product with water before applying it in one or more ways.

Mix 1 teaspoon of fish and seaweed emulsion with 1 cup of lukewarm water. Soak seeds in the solution overnight before sowing the seeds in soil or potting mix.

Mix 1 tablespoon of fish and seaweed emulsion with 1 gallon of water to fertilize houseplants and seedlings. Water houseplants with the mixture every two to three weeks. Water seedlings with it every 10 days.

Combine 1/2 ounce of fish and seaweed emulsion with 1 gallon of water for use with transplants. Water the transplants with the mixture once or twice weekly.

Dilute 1 ounce of fish and seaweed emulsion in 1 gallon of water. Fill a spray bottle with the solution, and use it to mist the leaves of flowering plants, vegetables, trees and shrubs every two to three weeks. Apply the solution until it drips off the leaves. Use the solution in early morning or late evening for its best results. Plants absorb the fertilizer via their leaves.

Mix 1/4 cup of fish and seaweed emulsion with 1 gallon of water. Combine the diluted emulsion with your compost every two to three weeks.

Watch the video: Homemade Fish Emulsion as Organic Fertlizer