How to Use Worm Castings Explained!

how to use worm castings
Experts recommend at least one cup of soil to one part worm manure (1:1) ratio for seed planting. Use at least four pounds of worm castings per gallon of soil. Planting directly on casts without first mixing with soil is not recommended.

Worm casts are a byproduct of vermicomposting, a natural process. The process begins when worms consume microbes deep in the soil. They then digest the organic matter to produce worm juice, a nutrient-rich liquid fertilizer (vermicompost tea).

The rehashed material (dry form), broken down into tiny particles, is known as worm castings or vermicastings. Other people refer to it as vermicast or worm manure. 

The rich dark humus contains nutrients, such as nitrogen and phosphorus, that improves plant growth. They also have a variety of trace minerals, such as calcium, magnesium, and potassium.

Worm castings are superior to chemical fertilizers because they emit much-needed nutrients into the soil through a slow release process.

This is particularly beneficial for plants that require only a small amount of organic matter, such as tomatoes and lettuce. 

How Much Worm Castings Should You Add to Soil?

There is no hard and fast rule for determining how much worm castings your vegetable garden will require. The good news is that a small amount of vermicast can go a long way. Experts recommend at least one cup of soil to one part worm manure (1:1) ratio for seed planting. 

If you’re wondering how much worm castings to add to the soil for mature, healthy plants, use the same or slightly less percentage. Some homeowners use about a quarter cup of casts in each planting hole for perennials and vegetables.

However, how much worm castings per gallon of soil are needed?

Use at least four pounds of worm castings per gallon of soil.

 During the growing season, use worm manure as a top dressing to stimulate the potting soil. In addition, a cup of vermicast works perfectly in each planting hole for trees and shrubs.

Can you plant directly into worm castings?

Planting directly on casts without first mixing with soil is not recommended.

Most people are unaware that this prevents the roots from accessing necessary organic matter and growing properly.

How To Use Worm Castings in Potted Plants

Spread an inch or so on top of the soil. During transplanting, thoroughly mix vermicast dust into each planting hole. 

Alternatively, use it as mulch to encourage the growth of beneficial microorganisms in the soil.

The benefit of using worm castings in potted plants is that they do not wash away during a heavy rainstorm or watering process. The same applies to hanging baskets and potted plants.

How Often Should You Use Worm Castings?

The question of how often to use worm castings is open to debate. Some people believe that adding them to the soil is best done once a month or season. Others argue that yearly applications are sufficient. 

In some areas, depending on how much rain falls, worms may lay more eggs and produce castings several times over a year.

The frequency of use depends on the plants you intend to grow, the season, and the availability of casts.

Can You Use Too Much Worm Castings?

In contrast to commercial fertilizers, there is no harm in using too much castings on the garden soil.

You see, most organic fertilizers have a lower NPK ratio of nitrogen to phosphorus. Worm castings have an average NPK ratio of 5:5:3 and, therefore, cannot burn your plants’ roots or damage the soil structure even when used in large quantities.

How Long Does it Take for Worm Castings?

When used correctly, worm compost bins begin bearing fruit after three to four months. Remember, worms will continue producing worm castings as long as you feed them.

The best way to accomplish this is to add food daily, so the worms always have something to eat. Pour a gallon of water into each cup of castings for faster results.

How Long Do Worm Castings Last in Soil?

Worm castings last in the soil for years if exposed to air and water. They can live for decades in soilless growing mediums.

If you intend to preserve your worm castings, sprinkle some water and cover it with wet paper or newspaper. Put it back in the bin and cover it with a lid.

This ensures that the castings remain aerobic and moist for a long time. Keep on checking the moisture after every six months.

In the long run, preserved castings are especially helpful when growing veggies that need lots of nitrogen or calcium, such as tomatoes. The abundant organic material is also advantageous to hydroponic plants (grown without potting soil).

How to Make DIY Worm Castings

1. Get some Worms and a Bin

Use red wiggler worms, which are the most active. You can purchase them online or from your local bait shop.

Ensure you get them within 24 hours of shipping to avoid dying in transit.  

2. Moisten the Bottom of Your Bin with Water and Line it with Newspaper

 Add two inches of compost material to help bacteria break down organic matter into plant nutrients.

3. Put Your Worms in the Bin and Leave Them Alone 

Add more compost material as needed to ensure they have enough food and moisture. Worms will consume all organic matter in your trunk, leaving worm castings behind.

4. Harvest Worm Castingg

When your worms have finished eating, remove them from the bin and replace them. Harvest worm castings and store them in a plastic bag.

The compost is ready when it turns dark brown or black, crumbly, and moist.


Discovering composting as a way of life or even better, as nature’s way of recycling, Ana dedicates her time to trying out new methods of composting at home. Her goal is to share everything that she’s learned in the hopes that it will help others discover the amazing rewards of composting.

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