Worm Castings Benefits and Disadvantages


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Worm castings are highly desirable for any gardener who uses compost. For years, gardeners have encouraged and attracted worms to their soil, reaping the benefits of these underground workers.

Deep underground, worms break up the earth, aerating it and allowing plant roots to grow. Near the surface, compost worms eat decomposing matter and leave nutrient-rich castings in their wake.

Harvesting and using this wonderful “black gold” is gaining popularity, but what are the real benefits of worm castings? And, more importantly, what are the downsides to using worm poop to fertilize your plants?

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This article will cover worm castings benefits and disadvantages. 

Top Benefits of Worm Castings

There are many advantages of using worm castings to fertilize your plants. In the wild, compost worms live in the top few inches of soil, eating rotting plant and animal matter, and enriching the topsoil.

However, this natural soil replenishment has been disrupted in many areas due to chemical-heavy plant treatments.

As people re-discover the importance of natural processes, composting methods like vermicomposting are becoming more popular.

Here is a list of the top worm casting benefits.

1. Worm Castings Enrich Soil Structure

Worm castings are full of nutrition and beneficial microorganisms for healthy plant growth, and they are also a dense organic material itself. All of these factors will help improve the condition of the soil.

Good soil structure means that it can facilitate moisture retention, as well as soil aeration.

These assets make worm castings the ideal amendment for all types of soil. Worm castings will help maintain levels in sandy soil and lighten heavy clay.

Vermicompost Worms

2. Worm Castings Act as an Insect Repellent

Adding worm castings to the earth around your plants will successfully control the populations of spider mites, whiteflies, and aphids. This helps reduce pesticides that use harmful chemicals to repel pests. 

Worm castings help lower the pest population on plants that have been mulched and fed with worm castings. They contain a certain enzyme that pests don’t like and will stay away from.

Pest populations on plants fertilized with worm castings are substantially lower than those that have not had access to castings.

3. Disease-Preventing Properties in Worm Castings

One of the findings of the numerous studies conducted on the benefits of worm castings is that they can suppress some soil-borne diseases to preserve soil health.

It has been found that the valuable bacteria in worm castings can prevent pathogens found in the soil from infecting seeds and seedlings.

4. Use Worm Castings as a Compost Starter

Worm castings are an excellent compost starter if you are beginning to compost outside. They can kick-start your compost pile’s ecosystem.

The microbial activity in worm castings can also improve the health of your compost heap. 

5. Worm Castings Improve Plant Growth

Plants need nutrients to thrive, and worm castings are one of the best sources of them, acting as a natural fertilizer. Healthy soil is at the top of the list for improving plant growth.

If you feed plants with worm castings regularly, they’ll be healthier and grow faster. The high nitrogen content of worm castings helps plants produce more leaves and flowers. 

6. Worm Castings Help Plants Grow Stronger Roots

Another benefit of worm castings being used as an organic fertilizer is their ability to strengthen plant roots for indoor and outdoor plants. 

When added to a potting mix or garden soil, worm castings will increase root mass. This will allow plants to absorb more water and nutrients.

7. Worm Castings Make Fertile Soils

Worm castings can be used to improve fertility in soils that are low in organic matter. How great is that? 

Worms turn organic waste like food scraps and other kitchen scraps into earthworm castings that provide beneficial bacteria and enzymes for healthier plants.

They’re rich in nutrients such as phosphorous, potassium, calcium, magnesium, iron, and manganese.

Vermicomposting Worm Castings

Top Disadvantages of Worm Castings

I can honestly say that there are not many disadvantages to worm castings. I can only think of one!

To pad out this list, I’ve included a couple disadvantages and a common mistake of vermicomposting (the process of using worms in a compost system to harvest worm castings.)

1. Limited quantity.

Unless you are prepared to dedicate a relatively large area to your worm farm, you will have limited worm castings compared to regular composting.

As worm castings take time and space to make, they can be more costly to buy than regular compost. If you have a large area to dig over, worm castings are possibly too expensive to use.

This factor is the only real disadvantage of worm castings, as in every other way, they are the perfect fertilizer and soil amendment.

2. Temperature Changes

Worm systems need to be protected from weather extremes to ensure the survival of your worms. After all, worms are still living creatures.

While regular open-air composting gives bugs the ability to come and go as they please, the worms in your worm composter have nowhere to go.

If your composter becomes too saturated with water, too hot, or too cold, your worms will either die or escape. Either way, this leaves you with a compost system that no longer functions.

If you live in an area where the temperatures can change dramatically from season to season, keep an eye on the health of your worms. You’ll also need to keep an eye on the moisture level as it can get too dry or too wet. 

3. Misuse of the Leachate

Leachate is the liquid run-off from the worm composter. A common mistake in worm farming is to use the leachate as if it was worm tea. 

Worm tea is made by “brewing” fresh worm castings or vermicompost, whereas the leachate run-off from your food bin is liquid from the decomposing materials inside.

Leachate is better thrown down the drain than used as a fertilizer, because leachate can contain harmful bacteria. If the leachate doesn’t have too much toxic bacteria, you can dilute it to use for watering your non-edible plants and pouring it on your outdoor compost heap.

The best test to check if the leachate is usable is to smell it. If it smells bad, then chuck it. Even if the leachate doesn’t smell, I would advise against using it on edible plants.

Should You Use Worm Castings vs Compost?

If you are unsure whether you need regular compost or worm castings, then I’ve created this handy guide to help you decide.

Based on the situation, this table will help you decide whether worm castings or regular compost should be used.

SituationWorm CastingsRegular Compost
Digging over a large area such as a vegetable garden.Chances are you won’t have enough worm castings to make this feasible. Buying a large amount of worm castings will be costly. You should use regular compost.If you need a large amount of organic matter, you should with regular compost. For best results, dig in the compost and then spread worm castings over the surface of the earth.
Making potting mixWorm castings are great in potting mixes for potted plants. They have more beneficial microbes than regular compost, and it is less likely that they will be contaminated with seeds or bugs.Regular compost can be used in potting mixes. However, for indoor plants, you may risk bringing bug eggs or seeds into your home through the compost.
Making liquid fertilizerWorm tea is an amazing liquid fertilizer as it provides all the benefits of worms casting in liquid form. It is perfect for houseplants, vegetables, and any other plant that needs a boost. You can put the discarded castings onto your compost heap or dig them into the soil once you’ve made the tea.Compost tea is beneficial too, just not quite as good as worm tea! If you have compost and want to make liquid fertilizer, it will do the job. But if you’re looking for something to create a liquid fertilizer specifically, worm castings are hands down the way to go.
As a soil amendmentLike digging over a patch of ground, worm casting may be too limited/costly to be effective. While they are an excellent soil amendment, they are probably best used elsewhere. This isn’t to say you can’t use worm castings as a soil amendment, but you may struggle if you have a lot of ground to improve.Compost comes into its own as a soil amendment. You can produce a lot of it, and it is cheap enough that you won’t break the bank if you need to buy it. Compost is a great soil amendment, adding many of the same benefits as worm castings. It helps moisture retention, aeration, and soil structure. The fact that the levels of nutrients and microorganisms are lower than worm castings doesn’t matter when you’re digging over a large area, and the compost will attract worms to your soil!

Final Thoughts on Worm Casting Benefits

The benefits of using worm castings are numerous, and there’s no doubt that they are worth exploring further. 

Worm castings are one of the wonders of the natural world. They demonstrate the symbiotic relationship that all animals (aside from humans!) have with nature. The more we discover the advantages of listening and learning from nature, the more hope we have that our species will survive.

So what are you waiting for? Get out there and start making some worm castings today!

Learn more about vermicomposting and worm castings: 

Worm Casting FAQs

Can you use too much worm castings?

No, you don’t need to worry about using too much worm castings. In fact, you shouldn’t be afraid to add all the worm castings that your worms produce. Just like compost, you’ll find that the more you add, the better the quality becomes. Worm castings are very rich in nutrients, so the more you add, the richer the soil.  

Are worm castings bad?

Worm castings are not bad and considered by many gardeners to be the ultimate fertilizer. Worms eat decaying organic matter and excrete their waste as quality worm castings. These castings are rich in nutrients and minerals, so they are great for plants. 

Will worm castings burn my plants?

No, worm castings will not burn or scorch plants or their leaves. That’s one of the best things about worm castings. They don’t have any harmful toxins like chemical fertilizers do. Another advantage of worm castings is that they act as a slow-release fertilizer too, so there’s even less risk of burning plants. 

How long do worm castings last in soil?

Worm castings stay active in the soil for 6 months up to about a year. However, they lose their potency as time goes on, so you should apply new batches every six months or so. Proper storage of worm castings is important. During the growing season, you can add more often as plants will absorb more nutrients to grow.

Are worm castings a complete fertilizer?

Worm castings are not a “complete” fertilizer, but they are a good source of nitrogen and phosphorus. They also contain trace amounts of other important nutrients such as potassium, magnesium, calcium, and sulfur. If you want to make sure you get all the nutrients you need, you can always supplement them with an additional application of a balanced organic fertilizer.

Can I use worm castings instead of fertilizer?

In many cases, you can use worm castings instead of chemical fertilizers. Worm castings are a great way to feed your plants without having to buy expensive commercial fertilizers. They provide similar results to synthetic fertilizers, but at a fraction of the cost and natural.

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Written by:

Denise Davis
I am an avid gardener who has spent most of her life in the garden, growing and cultivating organic veggies for friends and family. I love the earthy smell of composting and making homemade fertilizers from natural ingredients like old coffee grounds or eggshells. Gardening is a great way to get outside, learn new things about nature, exercise your body (and brain!) and eat healthy food you have grown yourself!