If you’ve been gardening for some time you would know that earthworms are beneficial to the garden. There are many types of earthworms, all with slightly different roles in the soil. Many gardeners (myself included) use composting earthworms to turn our food and yard waste into worm castings. Over time, the benefits of worm castings are becoming more well-known. More people are using their native earthworms to reduce their waste while also improving the quality of their soils. If you are new to worm farming or don’t yet know the benefits of worm castings we go through it in detail in this post.
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What are worm castings?
If you guessed worm castings are worm poop, you would be correct. As earthworms go through the soil they consume the organic matter in the soil or on the soil’s surface. The diet of different classes of earthworms can vary, but all earthworms consume some amount of organic matter.
At the other end, what comes out is worm castings. Worm castings are rich in microbial life, perfectly broken down organic material, full of nutrients that can be absorbed by plants.
Benefits of worm castings: What does worm castings do for soil?
The benefit of the microbial life found in worm castings can’t be understated. It is far more diverse than you would find in your regular compost. Worm compost is known to contain 3 very important components that exist in all healthy soils:
- Humic acid
- Mycorrhizal fungi and
- Beneficial nematodes
Humic acid
Humic acid increases the amount of nutrients that are available to plants in the soil. It also increases the soil microbial activity and acts as a root stimulant.
Mycorrhizal fungi
Mycorrhizal fungi help plants take up more water from the soil. Mycorrhizal fungi are also important in the aggregation of soil particles.
Beneficial nematodes
Beneficial nematodes are important. They help keep other microorganisms like harmful fungi and destructive nematode populations low.
Benefits of worm castings: Why are worm castings good for plants?
The effects of earthworm castings are usually immediately visible. Largely because a lot of the nutrients in worm castings are water-soluble. Some benefits of worm castings to plants include:
- Reduces the risk of pests and diseases that could affect plants. Worm castings suppress destructive nematodes and many soil-borne diseases.
- A source of slow-release Nitrogen. Worm castings are high in nitrogen. But, unlike chemical fertilizers (which we will discuss in more detail later) the nitrogen is released more slowly.
- A source of a wide variety of micronutrients. A great source of micronutrients. Worm castings provide a wide range of essential nutrients to plants.
- Improved development of flowers and fruit. Using worm castings can help plants grow larger and stronger. Pants produce more flowers, and bigger, healthier fruit and vegetables.
- Increased resistance to pests. Healthy plants are less prone to be attacked by pests.
- Improved water and nutrient uptake. Worm castings help the soil retain moisture for longer periods of time. Unlike heavy clay soils, worm castings don’t hold on to the water molecules too tightly. Plants are easily able to access the water (and water-soluble nutrients) available in the root zone of the plant.
Worm Castings Vs Chemical Fertilizers
When using chemical fertilizers it is estimated 80% of it never gets used by the plants. Most of what is applied to the soil either goes down into the soil beyond the root zone of the plant or is lost as runoff (and removed from the soil entirely). The latter can lead to environmental problems as chemical fertilizers are known to cause the eutrophication of waterways. Algal blooms in rivers close to agricultural lands is a telltale sign of this.
Unlike chemical fertilizers, worm castings is a slow-release fertilizer that feeds the plants over time. Nutrients are constantly being exchanged between the soil, its microbes and the roots around it. Because of this nutrient escape is less significant.
Additionally, a major benefit of worm castings is that it is the gift that keeps on giving. The beneficial microbes found in worm castings will continue to multiply in the soil. As these microbes multiply they will feed and unlock nutrients, making more nutrients available to the plant’s root system.
Can Worm castings burn plants?
It is highly unlikely worm castings will burn your plants. Largely because that’s just not the way nature made it. Earthworms break down organic matter, including that of animal manures. Earthworms are there to recycle decaying organic matter, cycling it back into something that can be used by the plants. From what I’ve seen, earthworms won’t start feeding on the organic material unless it is in a somewhat decomposed state. After they consume it and produce their castings it is in a state that is ready for plants to use.
How long are worm castings good for?
In most cases, worm castings can last up to a year in storage with no reduction of effectiveness. The key is to keep your castings moist (but not soaking wet) and aerated. Ensuring your casting have a good airflow during storage is something I see that most people overlook. The most important “ingredient” in worm castings are the beneficial aerobic microbes. In order to keep these microbes alive, they need to have a supply of air and adequate moisture.
How to use worm castings in the garden
Worm castings can be used in the garden in a number of ways. Worm castings can be used:
- To amend soil
- As a top dress
- As a foliar spray or a soil drench
How to use worm castings in soil
If you are starting a new garden bed or planter worm castings can be added to your potting soil or you’re regular garden soil. Worm castings work well in both clay and sandy soils bringing them to a more neutral state. As a soil amendment, you shouldn’t need more than 10% worm castings. A little goes a long way.
The nitrogen levels in worm castings can seem low compared to chemical fertilizers. However, the real gift is in the microbes that will populate the soil.
How to apply worm castings to plants
For already established plants worm castings can be used as a mulch or a top dress to your soil. For indoor potted plants, a handful of castings sprinkled around the base of the plant is all you need.
To apply worm castings to outdoor garden beds pull the mulch away from the base of the plant. Then, add your castings as wide as the leaves of your plants spread. Finally, replace the mulch layer. And yes, you should be mulching your plants. I go through all the details of why in this article.
As you water your plants the nutrients from the castings will filter down into the soil and continue to feed the plant for some time.
How to use worm tea
Worm tea or worm castings tea is a liquid fertilizer made from worm compost. To make worm tea you have to essentially mix your castings with water and add air and food to multiply the good bacteria present. If you are interested in learning how to make it, I’ve detailed the method I use in this article. The micronutrients in worm castings are dissolved in the water and can be utilized by the plant almost immediately
Worm tea can be used as a soil drench or a foliar spray. Its effectiveness as a foliar spray largely depends on how readily the plant can absorb nutrients through its leaves. Plants like tomatoes and cucumbers are very good at absorbing nutrients through their leaves. When foliar feeding always test a small area first before spraying the entire plant.
When to add worm castings to soil
Worm castings can be added to your seedling trays (after germination if you’re using a sterilized medium). At transplanting, you can add worm castings to the planting hole. This allows for a good concentration of beneficial microorganisms in the plant’s root zone.
Castings can also be added throughout t the life of the plant. If your soil is starting to show cracks or is drying out quickly adding some compost or worm castings could help get it back in balance.
How much worm castings to add to soil
If the plant is already growing, a handful or 2 of castings is all that you need around the base of the plant. If you are starting a new garden bed 10% castings will be more than sufficient. Above 25% castings will not provide any significant difference to the outcome.
Can I use worm castings as soil?
Using worm castings as soil isn’t something I would recommend. In my experience worm castings on their own tends to compress very easily. This reduces the pore space between the casting particles and reduces the amount of air available to the plant’s root system.
I’ve also noticed worm castings can become very hydrophobic. If they are left to dry out you may notice the water just sitting on the surface and not being absorbed readily by the castings. Therefore, this can be a potential problem if you go too long between watering.
Worm castings don’t have all of the nutrients your plants need. Sure it has nitrogen and trace minerals but it doesn’t have the potassium and phosphorus in the quantities needed to support plant growth. The biggest benefit of worm castings is that it has beneficial microorganisms. These organisms can aid in unlocking nutrients already present in the soil (i.e. the nutrients are in the soil but are not accessible to the plant).
Worm Factory 360 | Urban Worm Bag Worm Composting Bin | Hungry Bin |
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Final thoughts
Worm castings are full of beneficial microbes that add life to the soil. These microbes are important for unlocking nutrients already present in the soil. Additionally, the increased yield due to the presence of worm castings in soil has been well documented.
If you’re adventurous and want to get the most out of your worm castings you can try making a worm compost tea. Compost tea from worm castings can be applied to the leaves of the plant, as a soil drench or both. The nutrients in worm castings are water-soluble, making them immediate plant food.
Earthworms make a great addition to houseplants and gardens. Additionally, there is very little to fear when using worm castings since there is no evidence of worm castings ever burning any plant.
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