Algae As fertilizer What You Need To Know

Why Is Algae A Good Fertilizer

algae growing in the water
Algae producing in the water Andrea Pokrzywinski

While most of us are used to seeing algae as nasty scum that grow on our ponds and lakes. When it gets correctly prepared, it can make for a nutrient-dense fertilizer.

Unlike many synthetic bottled nutrients, algae is a much more reusable and environmentally friendly option.

Since I have been looking for more ways to use organic biofertilizers into my garden. I decided to find out how algae could possibly fill that role.

Why Is Algae A Good Fertilizer?

Role of Algae as a Biofertilizer

Algae is made up of living organisms. When added to the soil, they quickly break down. When breaking down, they release nutrients they contain into the ground.

While Algae are breaking down, they release beneficial nutrients into the soil.

They are known to contain macronutrients and micronutrients. They also usually have high levels of nitrogen and potassium that get released. [1]

The release of these chemicals into the soil is why Algae works so well as a biofertilizer.

Plants can use the nutrients from the algae to help fuel their plant growth.

Is Algae Good For Plants

Using Algae For Fertilizer

It is vital to make sure that the algae are already dead before using it with our plants.

Adding a lot of living algae to your soil will allow it to begin growing to the top of our medium.

We also want to make sure the top of our soil is dry between waterings. This will prevent any algae still alive from taking hold and growing all over the top of our medium.

If we let the algae get out of hand. It can attract bugs like gnats witch are a real pain to have around our crop. These little buggers will feed on the algae and our plant roots. This will increase the chance of having the plants getting a disease.

If you are growing your plants in a greenhouse, you need to pay extra attention. The continual moisture in these environments makes the perfect breeding ground for algae to take hold.

If you want to use algae fertilizer in your greenhouse. I suggest using the seaweed steeping method further below in the article.

This will allow you to extract the nutrients from the algae without bringing the organisms into your greenhouse.

When the algae grow on top of the soil, it reduces gas exchange, which can also slow root growth.

But using properly prepared Algae fertilizers will provide many of the nutrients needed to fuel plant growth. Adding them also helps to increase the amount of organic matter, improving our soil structure.

Algae in the soil will excrete carbohydrates whose molecules consist of several sugar molecules bonded together, increasing soil aggregation.

Algae Fertilizer For Soil

Algae is an eco-friendly and cost-effective way we can enhance our soil without degrading the ecosystem.

Another benefit is the rate algae can reproduce at. Some species can double their numbers within a single day.

With such a high rate of growth, we can continually use it without depleting our supply.

It can also help with the soil's water retention and create a more airy environment, which is excellent in promoting root growth.

Soil that used algae fertilizers had significantly lower levels of heavy metals. The plants that received it as fertilizer also had plants with more leaves, higher rooting, thicker stems, and higher yields than conventional fertilizer.[7]

How Is Algae Turned Into Fertilizer?

Homemade Pond Algae Biofertilizer

Algae You could collect from under a bridge
Algae You could collect from under a bridge Glynn
Step 1

Collect the algae from a lake our pond once it has started to grow into clumps. It will start off thin, but over time, these clumps will form, and that is when you want to harvest the algae.

A pool skimmer works really well as a way to extract the algae from your pond.

Try to collect them before they reach the blooming stage. Algae nutrient levels begin to drop when they are allowed to reach this stage.[2]

Step 2

Important if your algae are collected from saltwater, you must follow this step. If you gathered it from a freshwater source, you could skip this step.

Use clean water and thoroughly rinse the algae clumps. Algae growing in saltwater are known to be very rich in salt content. We want to remove as much of the salt as possible.

Step 3

Place down a tarp or cardboard etc. Break up the algae clumps into more refined pieces to help speed up the drying process. Sit them in a location that gets lots of sunlight. When the algae are dry enough to easily crumble, use your hands, and crush all the algae until the consistency is similar to soil.

Step 4

While it is best to mix the algae crumble into compost, potting soil should work just as well. Make sure you thoroughly mix the crushed algae into your medium. It is easier if you slowly add your crushed algae while stirring the soil.


Make sure the algae is very well dried out. This will help prevent it from growing on the top of your soil.

If live algae grow on top of the ground, it can cause problems for the plants. This is especially true for young plants or ones that are just beginning to sprout.

Homemade Seaweed biofertilizer

seaweed collected on the seashore
seaweed collected on the seashore

If you want to use seaweed, yes, this is a group of algae, check out the video below.

Before you just go collecting seaweed, it is essential to check your local laws before harvesting it.

According to Rak Seaweed Harvesting there are various statutes and regulations regarding seaweed harvesting depending on where you live.

Step 1

Collect your seaweed. Do not take living seaweed out of the water but collect it from the shores when it washes up.

Step 2

If collected from saltwater, you will need to thoroughly wash your seaweed to remove as much salt as possible.

You will also want to go through the seaweed removing any debris, fishing line, bottle caps, etc. that could have gotten mixed in with it.

Step 3

To make your life easier, use 2 buckets. Drill holes in the bottom of one and sit it inside of the other. This will allow you to easily collect the water fertilizer later.

Now fill the bucket with the seaweed you collected earlier. Use fresh water and fill the bucket to the top. Once filled, you need to place a lid over the bucket. Make sure the lid seals tightly around the bucket.

Step 4

Now let the bucket sit for 2 to 4 weeks. The longer it sits, the stronger your fertilizer will become. You can even allow your bucket to steeping for months to make it an extra potent fertilizer.

Steeping(letting it sit in the water) will allow the nutrients to get extracted from the seaweed into the water. Do not store in your house. The odor from the bucket can get a remarkably stinky smell.

Step 5

You will want to wear gloves and take care not to get the liquid on your skin. It is not dangerous to your skin, but the smell will linger on your skin if you let the liquid get on it.

Pull the interior bucket up, allowing the water to collect in the second bucket. And there you go, the collected water will be a natural biofertilizer you can use in your garden.

This form of liquid fertilizer will only store for around a month to month and a half.

Step 6

The watering ratio of seaweed fertilizer to the water.

Every week that you waited, you will add to the ratio of fertilizer-to-water. So if you waited 3 weeks to collect your fertilizer, use 1 cup fertilizer to 3 cups water. If you went four weeks, you would use 1 cup to 4 cups.

When you have a new batch of this biofertilizer, it is best to test on one plant before using it on your whole crop. This will allow you to find the ratio best for your plants with the risk of nutrient burn to only one plant.

After using the seaweed to make your organic fertilizer, you can add the remaining seaweed to a compost pile. While the nutrient value may be low, it will help with water retention and reduce soil compaction.

Blue-Green Algae Promise To Help Boost Food Crop Yields


While algae can make a great biofertilizer. I am still unsure if I am comfortable adding it directly to my growing medium.

Using the seaweed method, where you steep the nutrients out of the plant material into water, makes me feel more comfortable.

But I grow indoors where my medium can sometimes stay damp longer than it would be compared to outdoor crops.

To prevent algae from growing, we can reduce the amount of light to reach our soil by covering the ground. Or make sure you allow the top of the earth to completely dry.

Sunlight feeds algae, so if we can prevent the amount of light on the soil, it will help ensure that it will not be replicating.

Dampness is also necessary for these guys to grow. Allowing the top of your soil to properly dry will help make sure they do not actively take hold.

If you have a pond on your property that algae like to grow in. Converting it into fertilizer is a great way to help the environment while disposing of it in a reusable and eco-friendly way.

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