In general, gardeners do not make a distinction between vermicompost and vermicast. There is no clear winner when deciding which type of fertilizer to use, as the difference between them is often negligible. Although they offer the same benefit to plants, they are technically different terms.
Vermicompost and vermicast are both beneficial to plants. Vermicast contains more concentrated nutrients but is more difficult to produce than vermicompost. The production of vermicompost is safer for worms than some common methods of making vermicast.
Read this article to learn more about the differences between vermicompost and vermicast.
1. Vermicast Contains a Higher Percentage of Worm Castings
Vermicompost is not entirely made up of worm castings. Although it does have many castings, it also contains worm eggs and decomposed material, including some of the bedding. The exact ratio of castings to other materials depends largely on your vermicomposting system and the number of worms you have.
Vermicast, on the other hand, refers to the worm castings themselves. While it is impossible to separate castings from vermicompost completely, you can come pretty close. Vermicast is often advertised as 99.9% castings, but there is no real way of knowing the exact percentage without a microscopic study of each batch.
2. Vermicompost Is Easier To Make Than Vermicast
The process of making vermicompost and vermicast begins the same way.
Waste is added to the top of the worm bin that also contains bedding. It is then eaten and digested by the worms, who then excrete castings. The resulting material is often collected at the bottom of the bin, although some systems require separating the fertilizer out manually. That material is vermicompost.
For a more detailed process, see my articles “How To Make Vermicompost From Kitchen Waste” and “How To Make Vermicompost From Cow Dung“.
However, the material you are left with is a mixture of worm castings, decomposed material, and some bedding that has made its way through. To make vermicast, you need to separate everything from the castings.
There are two primary ways to do this:
Use Water To Separate Castings
- After you have collected the vermicompost, pour it into a large tub of water.
- Remove the worms carefully and set them aside. Returning them to the worm bin is the best option.
- Sift out the decomposed material. Most material will float while the castings sink to the bottom. Worm castings will also fall through a small sieve to separate the remaining matter.
- Drain the excess water from the tub.
- Let the castings dry out, and you’re good to go!
Feed the Vermicompost to the Worms Again
Another method for making vermicast is to put the collected vermicompost through the bin again. The worms will not eat their castings, so the second time through, they will consume the decomposed material and remaining bedding, turning them into castings.
Some gardeners choose to put the material through the bin several times, but one extra trip through the bin is usually sufficient to remove the majority of the decomposed material. You must use this method with caution to avoid starving your worms, which is discussed further in the last few paragraphs.
3. Vermicast Has a Higher Nutrient Density Than Vermicompost
The entire nutrient content in vermicompost comes directly from the worm castings. The other material has no value. So, it makes sense that when you separate out the castings, they would have a higher nutrient density.
Vermicompost and vermicast both contain many nutrients:
- Nitrogen: Used to help plants produce amino acids and proteins.
- Magnesium: Used to absorb phosphorus, and helps produce chlorophyll.
- Iron: Used to make chlorophyll as well as improve leaf health.
- Zinc: Improves plant reproduction and helps with water retention.
- Phosphorus: Used to strengthen plant roots and keep away disease.
- Calcium: Used to bolster the plant structure and help the plant maintain a neutral pH level.
- Potassium: Helps plants to survive in very hot environments.
- Boron: Helps with calcium absorption as well as plant reproduction.
- Copper: Helps to prevent rot in plants.
- Sulfur: Helps absorb all of these nutrients and create protein.
All of these nutrients help plants with the following biological functions:
- Produce more flowers and produce.
- Be brighter and more vibrant in color.
- Grow faster.
- Retain more water and become less dependent on frequent watering.
- Stay healthy by killing potentially harmful bacteria.
The increase in nutrients is not beneficial for desert plants. Used to sandy soil without many nutrients, desert plants have evolved not to require as many minerals as plants from other climates. This unique adaptation makes desert plants such as cacti and succulents particularly sensitive to an abundance of nutrients.
This susceptibility means that vermicompost should be used in very small amounts for desert plants, and vermicast should be used even more sparingly or avoided altogether.
4. Vermicast Covers a Larger Area Than Vermicompost
Since vermicast is denser in nutrients, you need less vermicast than vermicompost for the same area. This difference is very important for the health of your plants. Using the same amount of vermicast as you would vermicompost can lead to nutrient toxicity that will quickly kill your plants.
Nutrient toxicity occurs when the plant has too much of a nutrient. This can present itself in different ways:
- Stunted growth
- Death of leaves
- Damage to the roots
When there are too many nutrients available to a plant, it will take in too much of one mineral. This will then block the roots, preventing the plant from absorbing other essential nutrients.
While prices vary, needing less vermicast than vermicompost may save you money, particularly if you need large amounts for an expansive garden or field.
5. Vermicast Can Be Harmful to Worms, Unlike Vermicompost
Not all of the processes for creating vermicast are safe for the worms. The health of the worms depends on how the vermicast is made.
When vermicast is separated using the bin of water method, the worms need to be taken out of the water. This technique is perfectly safe for the worms. Worms do not have lungs, so they cannot drown. As long as they are placed back in an environment with a good food source—like our vermicomposting bin—within a week, they should be fine.
The other method of separating worm castings involves feeding the already processed material back into the worm bin. Although this is not always bad for the worms, it can pose serious risks for the worms if not appropriately handled.
This vermicasting method poses a severe threat of starvation, especially when the material is fed back through the system more than once. Worm castings are the worm’s excrement. Since they have already been through their body, the worms have taken the nutrients they need and the substance will no longer have any nutritional value.
The worms then must rely on the remaining decomposed waste to sustain themselves. Redworms eat their weight in waste every day, and they will starve if there is not enough edible material in the bin.
When vermicompost is fed through a third time, there are barely any nutrients left for the worms to eat, and they will die of starvation within a few weeks. The more worms you have in your bin, the fewer nutrients they will each get; as a result, they will begin to die off rapidly.
Vermicomposting is less dangerous because it provides the worms with new material that is entirely edible and will give them enough energy. As long as there is a food source in the bin, there is no threat to the worm’s health.
Although vermicompost and vermicast are very similar, there are a few key differences in the process and nutrient content.
Vermicompost is made in a multi-tiered bin that collects a mixture of worm castings, decomposed material, and worm eggs. To make vermicast, you have to remove the eggs and undigested material.
Using water to separate vermicast is a more intensive process, but it is safe for your worms. Feeding the vermicompost through your worm bin multiple times may be easier, but there is a risk of the worms dying of starvation.