Seaweed Fertilizer: When To Use Seaweed Extract In Your Garden

Seaweed fertilizer is essentially plant food just like bonemeal fertilizer

Fertilizers made from seaweed are a great source of nutrients and trace elements (absorbed from the sea) for plants grown in containers or even those grown on the ground. 

Seaweed Fertilizer Extract

They’re eco-friendly and sustainable and contain micronutrients to enrich your soil. 

You may find it by different names such as bladderwrack or kelp.

Although most seaweed fertilizer is marine kelp, freshwater seaweed is also rich in nitrogen and phosphorus and may be used to supply nutrients to your plants.

What Is Seaweed Fertilizer?

Seaweed may be used whole, as a liquid or it may be composted and crushed before it is added to the soil as fertilizer. 

There are different types of seaweed fertilizers generally made of kelp extract and found in varying forms such as:

  • Liquid Seaweed Fertilizer– best for plants grown in containers since it soaks through easily and plants get nutrients faster.
  • Seaweed Extract Powder– this is a very potent fertilizer and is obtained by drying out all the water from seaweed. 
  • It is extracted from brown seaweed such as Ascophyllum Nodosum, Laminaria, etc.  
  • Seaweed/ Kelp Meal– this is essentially dried and crushed seaweed.
  • Calcified Seaweed– this one isn’t kelp fertilizer. 
  • It is a mix of calcified coral and algae (with around a 50% calcium content).

There are many different brands of seaweed fertilizer with Neptune’s Harvest (Amazon) being one of the more popular options. 

Their liquid fertilizer has an indefinite shelf life since they are only activated once the water is added to them.

How Do You Use Seaweed Fertilizer in The Garden?

Seaweed fertilizers help improve your plants’ health. 

They may be applied to the soil as mulch or mixed in with the compost pile. 

Avoid rinsing the seaweed beforehand to remove the salt as this will take away many of its positive micronutrients and alginates. 

The salt may get washed out by rainwater or hose down the soil after applying the fertilizer.  

Alternatively, seaweed fertilizer can be applied through a foliar method – applying it directly onto the leaves. 

Before you begin, check for and remove any dead or decaying leaves. 

Use a diluted form of liquid fertilizer (liquid kelp) and spray it in the form of a light mist over the leaves. 

You may either use a foliar spray for this or attach the liquid with your hose and fertilize while watering the plants.

Some gardeners may use a combination of seaweed and fish fertilizer to fertilize their house plants -this seaweed and fish emulsion (liquid fish) is sprayed in the foliar method.

How Much Alfalfa Meal Should I Use?

Organic fertilizers are best for plants. 

Many gardeners use a combination of Alfalfa meal and kelp (or seaweed fertilizer) to complete the NPK (Nitrogen- Phosphorus- Potassium) content of the soil. 

Alfalfa meal is derived from alfalfa grass and is rich in nitrogen and calcium.

Use the following list as a guide for how much Alfalfa meal you need to use:

  • 12 lbs/ 1000 square feet for a light coat (¼ cup per plant)
  • 25 lbs/ 1000 square feet for a regular coat (1/3 cup per plant)
  • 50 lbs/ 1000 square feet for a heavy application (1/2 cup per plant)

What Are the Benefits of Using Seaweed Fertilizer in Your Garden?

Seaweed products are beneficial to your garden in a number of ways:

  • It contains nutrients such as NPK and magnesium as well as growth hormones encouraging healthy plant growth.
  • It is a form of mulch keeping the soil damp and reduces the amount of water needed.
  • It reduces the frequency with which you need to weed your garden since it doesn’t contain any seeds (possible weeds).
  • It keeps your vegetable garden free of pests such as slugs, worms and even birds since all these creatures despise the texture and saltiness of fresh seaweed.
  • It helps plants build immunity against fungi and diseases.
  • Unlike dry fertilizers such as compost and other mulches, seaweed doesn’t blow away in the wind.
  • Seaweed fertilizer keeps the soil aerated and healthy.
  • It enriches plants grown by hydroponic by providing them with the nutrients plants generally extract from the soil.

Are There Any Downsides to Using Seaweed Fertilizer?

Since it is an organic fertilizer, seaweed fertilizer doesn’t really have any significant problems. 

One of the main issues is its high salt content and this isn’t particularly detrimental for plant health. 

As mentioned previously, the salt may wash out with the rain or when you water your garden.

Another minor issue is when it is applied as a mulch, it may break down faster than it can enrich the plant. 

Again, this is avoidable by applying it using the foliar method or mixing it in with the compost heap.

Other than this, there aren’t any significant downsides to using seaweed fertilizer.