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In this article, we compare worm castings with kelp meal to determine which of the two organic fertilizers aid plants better. We identify the features of each fertilizer, explaining why we recommend one over the other as compost for your garden.

If you take plant care seriously, organic fertilizers should feature prominently in your home garden compost pile. In contrast to chemical fertilizers, they aren’t harmful to microorganisms in soil. They’re also a slow-release source of nutrients and trace minerals like potassium, phosphorus, nitrogen, and calcium. 

Worm castings and kelp meal are similar in that both organic fertilizers provide the above-mentioned benefits, albeit in different ways. However, there are also stark differences between the two. Read on to find out what they are and how they can help your garden plants bloom!

Our Pick

Our organic fertilizer of choice is worm castings. To be fair, both organic fertilizers do a fine job of aiding plant growth. However, worm castings go the extra mile by acting as a soil conditioner that promotes healthy soil, too. Worm castings aerate the soil, improving its structure and allowing it to retain water. At the same time, the bacteria present in the castings are an excellent source of nourishment for microbes in soil. They’re great fertilizers for any garden plant.

About Worm Castings

  • Rich in trace minerals and nutrients like potassium, phosphorus and calcium
  • Provides plants with easy to absorb essential nutrients 
  • Improves soil quality, drainage and moisture retention
  • Contains bacteria that are helpful to microbes in soil
  • Not harmful to seedlings despite containing 4% nitrogen

Worm castings are the waste-product of earthworms: put simply, they’re worm poop. Earthworms are industrious little critters when it comes to breaking down organic matter. They really go to town as they consume, refining the nutrients in organic matter to their simplest form. This helps the plants absorb these nutrients easier.

As organic matter passes through the worm’s digestive tract, a coating forms around the excrement. The resulting compost serves as an excellent fertilizer and soil amendment packed with nutrients and trace elements that are very beneficial to plants like potassium, phosphorus, nitrogen, and calcium, among others. And though other fertilizers with nitrogen (like fish emulsion) tend to burn plants if used in too high quantities, you don’t have to worry about that with worm castings. 

However, it isn’t just the plants that benefit from this organic fertilizer: your garden soil also stands to benefit from the application of worm droppings as fertilizer. How? Well,  they’re also great for soil because they contain good bacteria that other organisms dwelling in the soil feed on. They also improve the soil structure, aerating it and giving it a water retention enhancement. This helps nutrients move through plant roots easily. 

The red wiggler is the species of earthworm most commonly recommended for harvesting this organic fertilizer, due to the little critter’s high metabolism. And with all this talk of poop, earthworm castings don’t stink the way other organic compost like fish emulsion and cow manure do. They’re a must for gardeners who want the soil in their garden’s soil to be healthy and rich in minerals


  • Not a smelly type of compost
  • You can make your own compost at home by getting your hands on some worms
  • Readily available fertilizer for purchase from garden centers in your area
  • Contains finely broken down nutrients, which help with plant root growth
  • Nitrogen levels present in the castings are not detrimental to plants


  • Not an option for organic gardeners who don’t want to handle poop

About Kelp Meal

  • Kelp meal is a combination of kelp seaweed and fish meal
  • Base ingredient has dual applications in the garden as either a foliar feed or foliar spray
  • Packed with micronutrients and macronutrients

If the thought of handling worm poop makes you squirm, you could instead try kelp as a fertilizer for your garden. Kelp is a type of algae. They are similar to seaweed and grow abundantly in the ocean. This makes them a highly sustainable source of fertilizer. 

Kelp can be processed in solid or liquid form in a wide variety of ways. When solid, kelp can be made into either kelp meal or an extract similar to dried seaweed. It can then be applied as a foliar feed. As a liquid fertilizer, it is cold processed and can be applied as a foliar spray on plants. It is highly concentrated in this form. As such, if you go the liquid kelp route ensure you follow the product package directions to the letter. 

Kelp meal is a mix of kelp seaweed and fish products, which, when combined, make a great growth stimulant for plants. The kelp seaweed and fish meal combo is packed with micronutrients and macronutrients like phosphorus, potassium, and nitrogen. It also contains trace elements like magnesium and iron. These elements benefit the crops in your garden by boosting their yields. They’re also good for the overall well-being of the plant.


  • Highly sustainable source of plant fertilizer
  • Rich in minerals, including those found in the ocean
  • A great alternative to worm castings for squeamish organic gardeners


  • Minimal benefits to soil in comparison to plants 
  • Unlike worm castings, you can’t make your own at home

Similarities Between Worm Castings and Kelp Meal

Earthworm castings and kelp are organic fertilizers that have a lot of things in common. 

First of all, both of these organic fertilizers are good sources of trace minerals like potassium, phosphorus, and nitrogen. As has been mentioned before, these minerals are beneficial to plants when absorbed at the roots.

Secondly, both are a 100% organic fertilizer and don’t contain chemicals that are harmful to microbes in the soil.

Finally, they’re both great as a compost pile for gardens large and small.

Differences Between Worm Castings and Kelp Meal

The main difference between the two organic fertilizers is that worm castings provide benefits to both the plants and soil in your garden. This means that trace minerals in kelp meal don’t flow through soil as well as the ones found in earthworm castings. 

Another difference is that you can make your own worm castings whereas you can only obtain kelp meal at your local garden center. 

Finally, foliar sprays can be derived from kelp, which is the base ingredient of kelp meal. Whereas worm castings are primarily a solid fertilizer.


If you’re looking for a fertilizer that will make your garden flourish, you can’t go wrong with earthworm castings. Though kelp meal provides plants with the same beneficial minerals, earthworm castings go further by helping improve your garden soil as well.

Grow Bigger Plants with Simple Grow

Do you wish your plants would grow bigger? Was your garden less than it should've been last year?

If you're tired of growing puny vegetables and fruits, it's time for an upgrade...Simple Grow Worm Castings!

What are worm castings? Another term for worm manure. Why would you want to use it in your garden, raised beds, and house plants? Because it makes them grow bigger, faster and healthier...with no chemicals!

How do worm castings do this? It's like giving your plants a powerful multivitamin with everything they need to grow. Trace minerals, nutrients, and most importantly...worm castings are chock full of beneficial microbes. Why does that make a difference?

In recent years, we've learned the importance of gut bacteria for humans and know that it impacts so many different parts of our health. The same thing applies with worms. Gut bacteria from the worm's digestive tract gets into the soil from the worm castings and promotes plant health. Plants have a symbiotic relationship with the microbes from the worm's digestive tract. Plants respond to it and grow really big...really fast!

If you've never tried worm castings before, you owe it to yourself to give them a try. Instead of using traditional chemical fertilizers from the big box store, why not try fresh, certified organic worm castings this year? You'll be able to grow bigger, healthier plants that you actually can feel good about eating. 

Take advantage of our special bundle sale on 25lb bags today!


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