Worm Casting: What It Is, Its Benefits, How to Make and Use It

Worm casting—you’ve probably heard of this miracle material before, but you don’t quite know what it is. You can use worm castings for many garden applications, including as a soil base or fertilizer. Let’s get right into the basics of worm casting and see how it can help you!

What is Worm Casting?

Worm castings are the waste materials created by earthworms. Yes, you heard that correctly—worm castings are worm poop. As the worms eat through compost or soil, they absorb certain nutrients that make their waste the perfect material for soil enrichment. 

According to the University of California, worm casting contains iron, sulfur, and calcium in optimal concentrations. They also determined the nitrogen, phosphorus, and potassium (NPK) rating to be 5:5:3.

a hand is holding worm casting


Benefits of Worm Casting

Worm castings can be a huge boon to plant growth. You can use earthworm castings to combat harmful soil pathogens by mixing them with potting soil. 

You can also use it as a fertilizer. Since worm castings have an NPK ratio that helps with growth, you should apply worm castings to your garden plants in the spring. 

You may see happier indoor plants if you use worm castings there too. All you need to do is apply a layer on the top of the soil and water to begin releasing the beneficial microbes into your soil.

Since worm castings are a naturally occurring substance, you can use them as lawn fertilizer without worrying about harmful side effects. You can fertilize your lawn in the morning and allow your kids or pets to play later that day with no worries. 


How to Make Worm Castings

You can purchase worm castings online or from your local garden supply store, but did you know you can make it at home? The process of vermicomposting creates worm compost, but also worm castings as a by-product. Here’s how to do it!


Materials and Supplies

To get started, you’ll need:

  • Waterproof glue
  • Drill
  • Shredded newspaper
  • Non-metal screening material
  • One pound of dirt (free from chemicals and pesticides)
  • Water
  • Composting material and a separate storage bin
  • One tall plastic bin that can fit inside a second shorter plastic bin
  • Worms


How to Do It

The first step before we get into building your vermicomposter is collecting the materials. You should be able to find all the materials at your local garden stores, except the worms. 

You should get red wigglers, a type of worm that eats exceptionally fast. You can find these online for between $15 and $30 per pound. Now that you’ve collected the materials, let’s go through how to build a vermicomposter. 

On the taller bin, drill a one-inch hole on the side of the bin near the top. Repeat on the opposite side. Then, flip the bin over and drill four 1/4-inch holes on the bottom of the bin. These two worm bins will serve as the container for the worms and compost.

Cover all the holes with the non-metal screening and glue them on. Allow the glue to dry completely before moving on. Place the tall bin in the short bin. You do not need to drill or glue anything to the short bin.

The next steps are how to create a happy environment for your worms. Add the shredded newspaper, dirt, and water to the tall bin and mix until everything is consistent and damp. You want enough to fill the tall bin about three inches from the bottom.

Next, add the worms to the mixture. You’ll want to give the worms 24 hours to acclimate to their new environment. Make sure the mixture is damp but not soupy; otherwise, your worms won’t thrive. You’ve now created your working worm farm!

Feed your worms with household scraps and compost. You should feed your worms once a week. Dig a small hole in the dirt and deposit the food scraps there. Cover the compost with a layer of fresh newspaper and then cover totally with the soil already in the bin. 

Covering the compost helps the worms eat it faster. It also helps keep flies away since they can’t access food buried below the dirt. 


Editors’ Recommendations 

Using proper tools can make vermicomposting easier and cleaner. It’s not always easy to choose when there are so many options, so we pulled together some of our favorite composting tools to help you. 


How to Harvest Worm Castings

Now that you’ve built your vermicompost, you can start harvesting worm castings. The holes you drilled on the bottom of the bin should leak material into the smaller plastic bin. That material is your worm castings. 

To harvest them, remove the top bin from the lower bin. Scoop out the material in the bottom bin and store it in a container. You should only need to clear the bottom bin every couple of months, but you can do it more often. 


How to Use Worm Casting

Worm castings help plant growth by applying a nutrient-rich material to the soil, thus giving the plants a healthier diet. Depending on the application, you’ll use worm castings in dramatically different ways. 

For indoor potted plants, apply an inch to the top layer of soil and scratch it deeper into the soil. The earthworm castings will help the plant if it has any nutrient deficiencies. Re-apply every two months.

For outdoor plants, apply two inches to the top layer of soil and then work it into the ground with a spade. Worm castings will provide long-lasting nutrients to your outdoor plants. 

For your lawn, you should spread four pounds of worm casting for every 100 square feet of grass. After you apply the earthworm castings, use a sprinkler to ensure the castings absorb into the ground. 

You can also make “worm tea,” a liquid fertilizer made from dissolving worm castings in water. Soak one part worm casting in three parts water for at least 24 hours. You can use worm compost tea as is or water it down.

If you use the compost tea at full concentration, use roughly eight ounces per plant once a month to boost plant growth. If you water it down, you can put it into a foliar sprayer and use it as a nutrient booster for your outdoor plants. The concentration is four ounces of worm tea to one gallon of water for the watered-down mixture. 


Frequently Asked Questions

Here are some of the most common questions we get asked about worm castings.

How Long Do Worm Castings Last in Soil?

If you use worm castings as a fertilizer for potted plants, it’s recommended to reapply the castings every month. After a month, the primary nutrients have already deposited themselves in the soil, so you’ll need to reapply to get more plant growth.

Can You Start Seeds in Worm Castings?

Yes, you can, but you need to make a potting mix. An excellent soil mix for seeds consists of one part potting soil, one part fine compost, one part perlite, and one part worm castings. The compost and worm castings act like time-release fertilizer, giving your seeds nutritious soil to grow in. 

What Are the Disadvantages of Worm Castings?

Worm castings aren’t great for acid-loving plants. Since worm castings have a neutral pH, they don’t support plants that like an acidic environment.

If you’re making your own worm castings, getting enough casting to use as fertilizer can take months. The upkeep will also take a considerable amount of time. 

For most plants, worm castings aren’t enough. You’ll have to purchase other sorts of fertilizer depending on the plant you’re feeding. For example, once a tomato plant begins fruiting, you’ll need a fertilizer high in nitrogen and potassium, something worm castings don’t have. 

Can I Use Too Much Worm Castings?

Not really! Worm castings don’t contain any chemical fertilizers, meaning they won’t cause fertilizer burn on your plants if you use too much. Worm castings are essentially a time-release fertilizer made from organic matter. As you water, more nutrients are released, but never too much to damage your plant.


Wrapping Up

Worm castings are a fantastic tool for any gardener. From worm casting tea to its uses as a grass fertilizer, there are countless ways you can use worm castings in your garden. 

The beneficial microbes and organic matter in the worm poop create the perfect material to give your plants the boost they need to thrive. So, why haven’t you started using worm castings in your garden yet?

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The Green Thumbs Behind This Article:

Tiffany Lei

Tiffany Lei

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