What Are Worm Castings?
Have you ever noticed small piles of crumbly pellets in your garden or on your lawn, especially after a period of good rain? These are earthworm castings, the poop of our busiest and most beneficial soil aerators. Consider yourself lucky to see this on top of your soil.
Worm activity improves soil structure, aerates roots, and helps with water penetration. In addition, castings are slowly released, provide concentrated nutrients, and do wonders for plant health.
The Many Benefits of Worm Castings
Worm castings contain enzymes, beneficial bacteria, and humus.They contain no salt and cannot burn plants like steer or chicken manures. Worm castings, in a sense, moderate a plant's uptake of heavy metals as well as excess acidity or alkalinity from the soil. They provide an organic, water-soluble source of fertilizer that is rich in nitrogen, phosphorus, and potassium. In fact, the amount of potash is nearly 7x that found in regular fertilizers!
This translates into dynamic root growth and plant structure. It is also a great source of calcium, magnesium, and other micro-nutrients that are key to overall vitality. Adding them to your vegetable garden will boost yields and help prevent blossom-end rot on tomatoes.
In comparative tests, the plants raised with worm castings grow larger with better root networks and depth, produce more fruits, and resist more fungal diseases. Worm castings have been shown to help retain soil moisture and inhibit verticillium wilt, a common disease of tomatoes.
Another impressive benefit is the way it naturally repels insects. The digestive system of earthworms produces an enzyme called chitinase. This enzyme is a degrader of chitin, the substance that comprises the exo-skeletons of most insects. When used properly, worm castings help to repel chewing and sucking insects like aphids, whiteflies, and hard-shelled plant bugs. If an insect feeds on the leaves of a plant that has absorbed the chitinase, its stomach will soon begin to dissolve, and death will come quickly.
How to Use Worm Castings
An application of worm castings should be about 1" thick and a foot or so in width. Spread it out away from the trunk and around the drip line of the tree or shrub then cover with a 2" layer of compost. Castings can also be mixed 1c per gallon of water as a brewed tea and applied as foliar spray.
In areas where soil is dusty and unable to absorb water, plants suffer because moisture never makes it to the roots. This hydrophobic soil is a challenge, and worm castings can help! Mixed in equal parts with topsoil and compost and worked into the existing soil twice a year in early spring and late fall, the improvement will be quite noticeable. Minimal tillage, plant variety, and mulch will all work with these amendments to produce great soil. Saving leaves and spreading them for a nice top dressing will also encourage worm activity and provide shelter for lizards, a great form of natural pest control.
Vermiculture is the raising of worms, and it is quickly becoming a widespread hobby due to the benefits of compost and castings. It is the red wiggler, Eisenia foetida, that is used for this purpose. Preferring organic matter over soil, they are voracious decomposers. Another is the African nightcrawler, Eudrilus eugeniae, which is a great waste consumer.
The common earthworm, Lumbricus terrestris, is the one we find while digging in our gardens. They burrow deeply and serve to aerate the soil where they prefer to live. They will not survive in compost piles, but they will still benefit your raised beds and garden plots.
All earthworms produce the mineral-rich castings which help to give the soil good texture for better roots and nutrient absorption.
Easy Do-It-Yourself Composting
Worms can be easily raised in a simple bin or a special worm habitat.
Here are the items that you will need for this DIY compost.
- a plastic bin at least 2' x 2' and 1' deep
- a watering can or hose
- a small garden fork
- brown ingredients: newspaper, corrugated cardboard, coir, dried leaves, etc.
- green ingredients: fruit and veggie scraps, eggshells, coffee grounds, grass clippings, horse manure, etc.
- garden soil
- red wiggler worms
How to Build Your Compost
- To get started, drill 1/16" holes with 6" spacing on all sides of the bin, including the bottom. Worms like warmth and darkness and will stay to the center.
- Add 6" of brown ingredients like shredded newspaper. Loosely sprinkle garden soil on top.
- Add 3" of green ingredients like clean kitchen scraps and coffee grounds. Sparingly add more garden soil.
- Lightly water then thoroughly mix with the garden fork.
- Add red wiggler worms.
- It is important to keep the compost moist but never soggy. Think of a wrung-out sponge.
- Keep adding more brown and green waste as the worms eat it. Remember the 2:1 ratio.
- Turn the compost once every 1 to 2 weeks. When the waste becomes black and crumbly, you know it's ready.
The worms can eat 1/2 their body weight in one day! Two pounds of worms to a pound or more of compost is a good way to start. Worms can be removed by hand from the castings, or the castings can be sifted through coarse screens
Use Castings Early and Continuously
Earthworm castings are also available in most garden centers or online from Amazon. Some varieties have added minerals and nutrients as well as increased levels of chitinase.
Whether you choose to buy the castings or raise worms yourself, adding them to your garden is the best thing you can do to improve soil, increase yields, and prevent both pests and disease. Don't wait until the insects become a problem; apply the worm castings at the time of planting. (1 part castings can be added to 3 parts soil for a suitable planting mix.) Throughout the year, add more for continued insect and disease prevention and vigorous growth. I recommend quarterly applications for active crops and bi-annual amendments for general improvement of soil structure. Happy harvest!
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
Questions & Answers
Question: Does worm tea hurt beneficial insects?
Answer: Worm tea should not harm beneficial insects. The chitinase in worm castings acts more like a repellent if sprayed on the leaves, and a soil drench would eventually give the plant a more systemic resistance. As with other plant sprays, remember to avoid the heat of the day. The benefits of worm castings for plant health are numerous. You can use it without fear.
Question: Is the tea better for existing potted hibiscus?
Answer: Probably. It would be easier for a container. Remember to water first, then apply any feedings.
© 2011 Catherine Tally
Catherine Tally (author) from Los Angeles on August 11, 2020:
Hi Grayze. This is a great question! Normal worm castings added to the soil shouldn't be a problem, and they may help with the yellow oleander aphids. If buying commercial worm castings, I would avoid the brands that have added chitin just to be safe. I have given up trying to control the aphids on milkweed since they have never really harmed my plants.
grayze on August 10, 2020:
Thank you for this information. I have milkweed that gets overrun by aphids. I would like to use worm casting to help get rid of them, but I am concerned that the chitinase would be harmful to the monarch caterpillars?
Catherine Tally (author) from Los Angeles on June 14, 2020:
Hi James. Worm castings help plants grow well, improve resilience, and deter insects; however, they are not considered a pesticide. If you have a significant problem with Japanese beetles and stink bugs, a pyrethrin spray is your best approach.
james b lowery on June 14, 2020:
I want to control Japanese Beetle on my roses. I also want to control Stink Bugs in my Garden
Catherine Tally (author) from Los Angeles on September 26, 2019:
Thank you, Cynthia! So glad you were inspired by my article. I encourage you to check back and let us know how it goes. All the best! Cat:)
Cynthia Zirkwitz from Vancouver Island, Canada on September 26, 2019:
I have been thinking of getting some worms and doing this in my back room over the winter. Your article is very well written and inspiring! Thank you!
Catherine Tally (author) from Los Angeles on May 15, 2016:
To easily separate the castings from the worms and their eggs, you should have 3 empty plastic bins and 2 framed straining screens- one 1/4" mesh screen and one 1/8" mesh screen. Put the pure compost in the 1/4" one and filter the worms first. the soil will then go through the 1/8" screen to filter the eggs. The remainder will be the usable castings. The worms and eggs will be returned to the newer compost pile to continue their job of decomposing organic material.
Shirlee on May 15, 2016:
I guess I'm just not getting it. How do u separate the worms casting from the worms and the soil? So if I put a screen under my tub that is keeping worms then the casting fall thru and then maybe a catch pan under screen for the so call tea?
Annie Fenn from Australia on June 03, 2011:
Thank you so much for this valuable information, cat on a soapbox. I struggle with pest control in my organic vegetable patch. I started a worm farm in an old bathtub a few months ago, but haven’t taken off any castings as yet.
Will do so for my spring plantings and see how the pest problem goes this coming season.
Catherine Tally (author) from Los Angeles on March 29, 2011:
meghansmummy- I'm glad that I was able to teach you a new gardening trick. Thanks for following :>)
meghansmummy on March 29, 2011:
wow i never knew that x
Catherine Tally (author) from Los Angeles on March 06, 2011:
Thanks, Alicia- It's a pleasure to help out a fellow gardener!
Linda Crampton from British Columbia, Canada on March 06, 2011:
I love the information and details in your hub. You've given great advice to gardeners!
Catherine Tally (author) from Los Angeles on March 06, 2011:
Thank you, Will!
WillStarr from Phoenix, Arizona on March 06, 2011:
Very informative and useful Hub.