Do Worm Castings Really Help Your Garden Plants?

Thinking of using worm castings in your garden but aren't sure if you should? This controversial practice has been used for decades in many different gardening practices. But does that mean it's actually good for your garden? In this article, gardening expert and farm owner Jenna Rich takes a deeper look at worm castings, and if they are actually good for your garden plants!

Gardener holding worm castings in rich and moist soil

If you haven’t heard yet, worm castings are in. As in, you’re not cool unless you use worm castings!

In all seriousness, although using worm castings in your garden may seem a little strange, many scientific studies show huge benefits on all types of plants including herbs, flowers, vegetables, and houseplants.

Worm castings are something you can make right at home or purchase online. Then just sit back and watch your garden thrive. Keep reading to learn all about this trend that is hitting gardens everywhere.


The Short Answer

Yes, worm castings can be beneficial to gardens for a number of different reasons. They offer a variety of different science backed benefits, which include both healthier and faster growing plants.

The Long Answer

Close-up of worms mixed with potting mix on a white wooden surface. Worms have an elongated tubular, flattened body, reddish in color without appendages.
Worm castings are an organic fertilizer also known as “vermicompost” which is composed of worm excrement and acts as a soil enricher.

Castings is just a word scientists and gardeners use in place of “poo”, perhaps so that it is appropriate to talk about at the dinner table. It is sometimes referred to as “vermicompost” (vermi- means related to worms).

To someone not familiar with castings, they may just look like little lumps of soil or like little beads on the soil’s surface. When I was a kid, I used to see worm castings on the soil surface and think it was little tunnels from the worms, and I suppose I wasn’t too far off.

Take a look in your garden once the snow has melted. If you see little bumps along the soil, dig in and have a closer look. They are darker in color than the soil and should stay slightly clumped together when you squeeze them together in your hand.

If you can identify them, that’s a sign of good soil health! Keep in mind, their presence will be higher and more obvious in areas with lots of organic matter, which makes sense because that’s the stuff worms want to feed on.

What Are the Benefits?

Close-up of children's hands holding fertile soil and vermicompost with many earthworms over a gray worm farm in the garden, against a blurred background. The digestive processes of the earthworm turn organic matter into a good quality natural fertilizer for agriculture.
The presence of worms in the soil promotes better aeration of the soil, improves its structure, and provides nutrients.

It’s pretty commonly known that when worms are present in the soil, it’s a good thing, but do you know why?

Studies have shown that worm presence:

  • Helps aerate the soil and works in amendments
  • Improves soil structure and breaks up compacted or clay soil
  • Provides immediate nutrients to your garden plants
  • Decreases transplant shock
  • Increases growth of new transplants
  • Speeds up germination of directly sown seeds
  • Improves overall soil health
  • Adds organic matter, and in turn, helps retain moisture content
  • Increases microbiology diversity in soil
  • Helps break down plant debris
  • Helps healthy root growth
  • Helps balance soil pH
  • Decreases occurrence of soil surface crust
  • Adds microbes that help plants uptake nutrients
  • And much more!

Worm castings are a natural fertilizer that contain Nitrogen, Potassium, and Phosphorus as well as lots of micronutrients and minerals such as calcium, iron, copper, magnesium, and zinc, just to name a few.

Pro Tip: Using castings in your garden does not eliminate the need for other fertilizers. Think of castings as an immunity booster.

What are the Risks?

Close-up of a gardener's hand in an orange glove holding a Vermicompost fertilizer in a green spatula over a heap of fertilizer. Vermicompost fertilizer consists of worm castings and improves soil structure and quality.
The use of castings has only positive effects and no negative risks.

So far, there have been no shown negative results or risks of using them in your garden. Since their fertilizer is mild and released slowly over time, there is little risk of adding too much.

Moreover, there are no chemicals in worm castings, so there is no risk of roots being burned. You can use however much you’d like but a little goes a long way, making this a very efficient and inexpensive way to fertilize your garden.

Especially if you have your worm farm and are feeding them scraps from your garden and used coffee grounds. The only real risk of using too much is simply wasting the product and the money it cost you to make or purchase it.

How to Use Worm Castings

Using worm castings can be done in a few simple steps. I’ve outlined them below so you can get started with items that are most likely available around your home.

Step 1: Make an Extract

Close-up of a measuring cup filled with liquid vermicompost fertilizer on a burlap-covered table. The fertilizer is dark brown in color with light brown bubbles on top. There is also a white plastic bottle and a garden shovel on the table.
You can dip seedlings in worm cast extract to give them a boost of nutrients and reduce transplant shock.

Before you transplant your veggies, herbs, and flowers to your garden, consider dunking them in a casting tea first. Here is an easy DIY worm casting extract recipe you can make at home.

You’ll need:

  • 5-gallon bucket
  • Clean water
  • Long pole for stirring
  • Tray of transplants
  • About a cup of worm castings

Vigorously stir the castings into the water for about 5 minutes. Then, bottom water your trays with about a half inch of the worm casting extract before transplanting them. This will give them a burst of nutrients right before being transplanted, which should lead to less transplant shock, more vigorous growth, and eventually, higher yields.

Discard any unused mixture. You can throw it right on top of your compost pile if you have one.

Pro Tip: You can also use this extract as a foliar feed mid-season. Just spray directly onto the foliage of plants like kale, tomatoes, and peppers. In addition to the nutrients added, it’s also known to deter many pests from making the underside of leaves their home.

Step 2a: Mix into Potting Soil

Close-up of organic fertilizer mixed with potting mix in a large black tray. Organic fertilizer consists of worm castings and long earthworms.
It is recommended to mix thecastings with soil when growing vegetables.

Mix castings into your potting soil when stepping up or repotting vegetables or houseplants. Only about 20% of the overall mix should consist of castings. More than that will simply be a waste.

Step 2b: Mix into Garden Beds

Close-up of a garden shovel full of organic fertilizer with earthworms, over a raised garden bed with growing strawberries. The garden is lit by the bright sun. The strawberry plant has rounded green leaves with serrated edges.
Scatter the castings directly onto the soil as a top dressing.

You can sprinkle worm castings directly onto your soil to give it a jumpstart at the beginning of your growing season and before planting anything. Just work it in as you prepare your beds, and it will be there for your plants when you are ready to start growing.

You can also add them to garden beds that already have plants growing in them as a side dressing. Just be sure to water immediately after so they reach the roots and can take effect.

Step 2c: Using with Houseplants

Close-up of transplanting an Indian rubber tree into a white decorative pot. Men's hands hold a plant with a root ball in a pot and pour vermicompost into it to improve the quality of the soil. The plant has large, oval, smooth, dark green leaves.
You can also add some castings to houseplants.

Many indoor growers recommend tossing a few tablespoons of worm castings in houseplants each month. Certainly, you should try adding some when you repot your houseplants. You should see some benefits even when just a small amount is added.

Starting a Worm Farm

Top view, close-up of a male hand with red earthworms, over a compost blue bin full of food waste, coconut coir and worms.
To create your own worm farm, you will need red worms, a container, a coconut coir and food scraps.

There are several reputable and trusted sources that can help you start your first worm farm. Red worms are the best type of worm if your main goal is to get castings. They are highly active, reproduce quickly, eat a lot, and in turn poop a lot, resulting in lots of castings for your garden.

To make a worm farm from scratch, you’ll need:

  • A sturdy plastic container with a lid
  • A drill
  • Food scraps
  • Coconut coir
  • Small, hand-held rake
  • About one pound of red worms

Drill ventilation holes in the top and sides (above where the worms will live). Fill your bin with contents and mix in your worms.

Alternatively, you can purchase a worm farm, complete with worms from an online retailer which is what we did on our farm. It may be a little pricier than if you build one yourself, but all the contents you need come in the mail (minus the food scraps, of course). Then just set it up and add your worms.

Pro Tip: Starting and keeping a worm farm can be a very fun and educational activity to do with children. They can help with feeding, keeping track of the outputs and get their hands dirty in the process!

Caring For Your Worms

Close-up of a man's hand with a green spade full of dry pressed sawdust near a green box - a worm farm, in a garden near a wooden fence. The container is covered with a thick polyurethane cloth.
Add dry sawdust, newspaper, and any food scraps to your worm farm as needed.

Keep your worm bin somewhere that remains between 55°-75° and out of any harsh lighting. Be sure not to keep them close to a drafty door or fireplace.

Turn your soil and worms gently about once a week to keep the airflow going, adding dry materials such as sawdust or fresh newspaper to deter bugs and keep the smells down and any food scraps as needed. If you notice it is particularly wet, add more dry items like newspaper scraps or brown paper.

Pro Tip: If you’re not quite ready to dive into the world of worms or simply don’t have the ability to keep keep your own worm farm at home, you can buy castings online at online sources or visit your local worm farm. Use them as recommended above.

Feeding Your Worms

Do feed things like this:
Do not feed things like this:

  • Food scraps such as apple cores, banana peels,
  • Coffee grounds
  • Newspaper
  • Tea bags
  • Leaves
  • Dryer lint

  • Citrus
  • Dairy
  • Meat, fat, bones
  • Bread or yeast
  • Plastic coated papers
  • Garlic, onions, salt, pepper or other spices
  • Diseased plant matter
  • Treated wood products


If you aren’t sure, always double check with an expert whether you should toss something in your worm farm or not.

Fun fact: The grittiness of coffee grounds improves worms’ digestion by helping them grind up organic matter.

Frequently Asked Questions

Can I just use compost to improve my soil health?

Interestingly, the same items like grass clippings, produce scraps, and newspaper can be used to make both compost and vermicompost. The benefit is that it is more immediately available to your soil and plants because the worms have already processed the compost ingredients for us.

How do I know if it’s working?

Like any good experiment, simply do a side-by-side trial of a crop with vermicompost and without. Be sure you keep everything else the same such as water application, sunlight, and any other fertilizer added. Take notes and pictures, and keep track of yields and dates of harvest.

If I use more will my plants see more benefits?

No. Studies show that past a certain application amount, which is about 20% of the growing medium, will not result in any additional benefits. At that point, you would just be wasting the castings.

How often should I side-dress my garden with worm castings?

This really depends on your soil’s overall type and health, what you are growing, and how hard you work your soil throughout the growing season. Also, long-season crops like kale, tomatoes, and certain perennials might love a mid-season side-dressing.

Like with many other things in gardening, experimentation is key. You could start by adding vermicompost in the spring and fall as a general amendment and then maybe mid-season.

How do I harvest worm castings from my worm farm?

You can harvest castings one of three ways.

Hand harvesting is just like it sounds and is for those of us who have extra time to do the sifting.

Worm relocation involves adding a layer and new food to your worm farm to encourage your worms to move out of their current space, leaving you with just scraps and castings in a few days-a-week.

Screen harvesting involves sifting the contents of your worm farm through a screen, leaving behind just the castings.

Be as gentle as possible to make sure you don’t squish any of your worms in the process.

Final Thoughts

With the gardening season almost upon us, I think it’s high time we all give this simple, organically created amendment a chance. What’s better than naturally created fertilizer that has only benefits for your soil and plants?

Whether you start your own worm farm or purchase worm castings from an online retailer, I suggest you try using them in your garden to see what all the fuss is about. All you have to gain is higher yields, healthier soil and thriving plants, with nothing to lose!

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