How to Make Seaweed Fertilizer, Benefits

Introduction: Hello farmers today we will be discussing about how to make seaweed fertilizer. Seaweed has been used for centuries to develop soil and feedstock. Seaweed contains many nutrients that benefit plants. For years, farmers and gardeners who live near the coast have used seaweed to develop plant growth. Liquid seaweed is great nourishment for plants but it is different from most NPK fertilizer treatments. Seaweed contains a little K – potassium.  But it has several minerals, vitamins, and enzymes that are natural growth stimulants.

A step by step guide to how to make seaweed fertilizer

Seaweed extends the shelf life of fruits and vegetable plants if applied 10 days before harvesting.   Seaweed lengthens the life of cut flowers if they are sprayed with liquid seaweed a day or two before cutting. Liquid seaweed shouldn’t be used as only fertilizer. Nitrogen (N), phosphorus (P), and potassium (K) come from another source.

Seaweed fertilizers could be used as a soil treatment. And since most plants absorb their nutrients through the plant leaves, applying it with a foliar method will benefit the plant even more. As the plant absorbs sunlight, it will absorb the nutrients in the fertilizer. Alginates (sponge-like starches found in seaweed), hold water droplets near the plant roots, making moisture obtainable to them without drowning them.  They help enrich the soil by feeding a myriad of beneficial microorganisms.

Soaking seeds with liquid seaweed before planting will develop seed germination, root growth, and early seedling vigor.  Liquid seaweed can be used as a rooting solution. Place cuttings in a solution of liquid seaweed fertilizer and water until roots develop, then plant.  It reduces transplant shock and speeds root growth.

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A Guide to Making Seaweed Fertilizer.
A Guide to Making Seaweed Fertilizer.

Seaweed fertilizer is generally a kelp-derived soil-additive that is rich in micronutrients (it also has NPK content). It has been used for a long time, especially by farmers that live near the coast, and can be prepared in several ways. You can also add kelp directly to the soil (but it might take a while for it to break down).

Main ways you can buy seaweed fertilizer

There are four main ways you can buy seaweed fertilizer. They are;

Liquid seaweed – Liquid seaweed is probably one of the best options for container growers as applying liquid feed will mean that plants can access nutrients quickly. It is formed by soaking and straining kelp in water.

Seaweed/kelp meal – Seaweed meal is prepared by drying the seaweed and, in the case of powder, crushing it.

Seaweed extract powder – Powder is usually made by heating seaweed to obtain rid of all the water content. What is left is a solid and highly potent form of feed.

Calcified seaweed – Calcified seaweed is not made from kelp. It consists of several types of calcified coral and certain types of algae that are harvested from the sea. It consists of around 50% calcium along with the usual minerals so useful to plant growth.

How is liquid seaweed fertilizer made?

Liquid seaweed fertilizers are made from several species of seaweed that are washed, dried, milled and processed to enable the natural benefits to go into effect immediately upon contact with either the plants’ foliage or the soil itself. This speeds up the natural processes by converting raw seaweed into an easily applied and digested weed.

The harvesting process ensures the sustainability of the natural crop. Choosing healthy weeds growing under optimum conditions guarantees the best growth-promoting substance yield. Liquid seaweed extract is formed with no acid and no caustic or organic solvents. It is an organic product that has been extensively used in organic grower trials.

Composting seaweed fertilizer

Seaweed fertilizers that are bladderwrack, kelp or laminaria, can be either useful to the soil as a mulch (although it will tend to break down very quickly) or can be added to the compost heap, where it is a good activator. A perhaps less serious potential difficulty with seaweed is its salt content. While it is unlikely to add sufficient seaweed to seriously upset the balances of salt in the soil, it is not liked by worms, which will not live in it. It can be hosed down before adding to the soil to decrease the salt content or left to be desalinated by rainwater. Rinsing seaweed is risky as helpful alginates are potentially lost to runoff.

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Cost of liquid seaweed fertilizer

The cost of Liquid Seaweed Fertilizer is approximately Rs 50/Litre.

Seaweed fertilizers in modern agriculture

Seaweed is a multicellular marine algae, it is very important for the marine living renewable source, seaweeds wildly used for gelling and stabilizing agents for many food and pharmaceutical industries.  Soil fertility depends upon the fertilizer requirement of the plant or crop, now a day’s lot of chemical fertilizers commercially obtainable but the growth, yield, and fertility of the soil are very much reduced or damaged. Recent studies proved that seaweed fertilizer better than other fertilizer. The seaweed fertilizers contained a lot of nutrients, for example, nitrogen, phosphorus, potash and plant growth hormones, and trace elements. This seaweed fertilizer is used to enhance seed germination and plant growth or crop yield.

Effect of seaweed liquid fertilizer on plant growth

Seaweed consists of all the trace elements and growth hormones required by plants. There is a growing concern over the use of seaweed fertilizer. Today, there is a very high demand for environment-friendly agriculture for the production of quality and healthy food to nourish the increasing population.

Using seaweed as fertilizer for plants

There are many advantages to using seaweed in the garden, and many different ways to use it. Like most organic material, seaweed develops soil structure, increasing soil porosity while also improving moisture retention. Nutrients in the seaweed stimulate beneficial soil bacteria, creating rich, healthy soil for flowerbeds or edible gardens. For this reason, dried seaweed is tilled or turned directly into the garden’s soil. Dried seaweed can be put into compost piles, adding a power punch of nutrients.

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

Harvesting seaweed

It is easier to harvest seaweed from above the low water line and it will be less wet. Limit your impact by picking lightly from some areas. Each patch of seaweed provides food and shelter for various small marine species. Choose no more than a third of the seaweed from any patch, and move on to another spot.

Higher water temperatures tend to slow down the development of seaweeds. Most seaweed species produce the fastest from January to May and are at their most productive during the spring.  Their development rate slows down as the water temperatures rise from June to September, the slowest growth rate being in August. Once the sea temperature starts to cool in the autumn, the growth rate starts to pick up again, mainly after November. If you are cutting seaweed do not take the entire plant but leave a good anchor of at least 20cms to facilitate new development.

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Many benefits and uses of seaweed fertilizer

Some of the benefits of seaweed fertilizers can be given below;

  • Liquid seaweed solution promotes additional budding if useful as the plants are beginning to bud.
  • Seaweed has 60 trace minerals and ready-to-use nutrients containing nitrogen, potassium, phosphate, and magnesium. It contains hormones to encourage plant growth.
  • Like all mulches, seaweed helps to maintain soil moist thus reducing your need to water the garden. An application of seaweed will decrease how often you need to weed. It contains no seeds that can turn into weeds as bark mulch sometimes does.
  • Seaweed fertilizer extends the shelf life of fruits and vegetables if applied 10 days before harvesting.
  • Seaweed extract also boosts crop yields, and improves the resistance of plants to frost and disease, increases the uptake of inorganic constituents from the soil, bolsters resistance to stress conditions and reduces storage losses of fruit. Slugs particularly hate seaweed because of its sharp edges and salt. Birds and other pests dislike it for the same reasons.
  • Seaweed fertilizer promotes vigorous growth and helps deter pests and diseases on fruit, flowers, vegetables, lawns, etc.
  • Seaweed fertilizers are mainly useful in organic gardening. They have almost every micro-nutrient in a fully chelated (immediately available) form. The algae are also full of carbohydrates, which plants use as a building block. Numerous beneficial microorganisms use carbohydrates as a food source.
  • Seaweed fertilizer helps aerate the soil just like peat moss does, but it has the added benefit of delivering nutrients and minerals.
  • Seaweed fertilizers (particularly the alginates in the seaweed) act as soil conditioners. The alginates react with metals in the soil and form long and cross-linked polymers in the soil. These polymers develop the crumbling in the soil and swell up when they get wet. They retain moisture for a long time.
  • Seaweed fertilizer helps you to grow strong, healthy plants, and healthy plants resist fungus and disease.

Seaweed as mulch

You can use seaweed as mulch around the base of plants. Mulches help the soil retain moisture, and then plants do not dry out as quickly during hot and dry weather. Mulches help the soil maintain a more consistent temperature, which works well in both hot and cold climates. Seaweed mulch will break down and help plant growth by adding nutrients to the soil.

How to use seaweed in the garden

Fresh Seaweed can be harvested and added directly to the garden, turning it in with a fork and letting the soil do the rest then this is best done after the seaweed has been thoroughly dried. Seaweed can also be composted and it is important to incorporate other matter with it to bring air into the heap. On its own the seaweed bogs down quickly into a thick slime, impermeable to gas exchange, leading to anaerobic digestion and slow, smelly compost.

Fresh seaweed also makes a very good mulch. Use a good thick layer as it shrinks quite quickly after a few dry days.  It is useful for covering Green Manures if you do not want to dig them in. Dried Seaweed can be used in the same manner. In its dried form, it is easier to handle and can simply be incorporated into the soil or put into the planting hole before planting. In its dried state as a meal, Seaweed can be given to animals as a natural conditioner.

Leafy growth

Among other nutrients, seaweed consists of nitrogen. Seaweed is composed of up to 1.2 percent nitrogen, and then it delivers to plant roots when used as a fertilizer. Nitrogen is necessary for the leafy growth of plants. Plants often become larger when given seaweed fertilizer. Seaweed also contains potassium, which helps plants produce more vigorously.

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Improved fruit and flower production

Seaweed fertilizer increases corn crop yields. Seaweed fertilizers increase the production of a variety of crops, such as potatoes, peppers, cucumbers, strawberries, apples, okra, and oranges. It helps make grapes sweeter and gladiolus flowers larger. These improvements are likely because seaweed consisting of phosphorous, which is known for helping with healthy fruit growth.

Main hormones in seaweed

The main hormones in seaweed contain auxins, cytokinins, betaines, and gibbelerins. These hormones are necessary to plant health. Most of these are required in very small proportions but are important nonetheless.


There are several different auxins, and they all have their specific roles. One of their major functions is balancing the speed of growth. They have growth-stimulating and growth-delaying functions. They stimulate root growth and prevent bud forming or bud opening at the wrong times. This can play an important role in the production of the plant’s auxins because the enzymes formed with the help of trace elements from the liquid seaweed fertilizer play an important role in the formation of auxins.


Cytokinins are a group of important plant hormones. They initiate and activate growth processes. The cytokinins available in liquid seaweed extract stimulate growth with greater vigor because they mobilize nutrients in the plant leaves. They protect from marginal frost (up to -3 Celsius). Cytokinins retard the senescence (aging processes) in the plant.


Betaines play an important role in the osmotic processes in plants. They mainly help to increase the water uptake in plants and are extremely helpful in dry conditions. Betaines are particularly helpful to plants under stress.

Why use seaweed in your garden

Seaweed contains all the elements but most only in trace amounts and it does however typically contain useful amounts of iodine, copper, manganese, potassium, phosphorus, iron and zinc. It’s normally used straight up, as a compost addition, or as a brewed seaweed tea.

Seaweed is used as a great soil conditioner which helps build a healthy soil food web in your garden. Its liquid form is used as a foliar spray for ornamental and edible gardens alike.

Seaweed tea is known for starting strong seedlings and producing resilient vegetable plants (it’s a huge help against marginal frosts) as well as improving veggies transport and shelf life.

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  1. I am very glad to read seawood fertiliser. Recently i used it in my mustered cultivation which flowering very much and my knowledge of seawood fertiliser very much after reading in the sight. Surely I would like to use seawood fertiliser in my every cultivation. Many many thanks JAGDISH JI


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