Worm Castings: A Gardener's Secret to Success

Updated on August 27, 2017
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Catherine is a California-certified nursery professional. Her interests are birds, insects, integrated pest management, & organic gardening.

Worm Poop Is A Gardener's Gold.

Evidence Of Worm Activity

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 water penetration. In addition, castings are slowly released yet 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 which has absorbed the chitinase, its stomach will soon begin to dissolve, and death will come quickly. 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.

How To Use Castings To Improve Poor Soil

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.


The Red Wiggler Is Used For Composting.

Eisenia foetida, the red wiggler worm, is a voracious decomposer. It prefers organic material over soil.
Eisenia foetida, the red wiggler worm, is a voracious decomposer. It prefers organic material over soil.

Common Earthworms Aerate The Soil.

Lumbricus terrestris, the common earthworm known as a night-crawler, does nor survive in the compost pile but will enrich and aerate your garden beds.
Lumbricus terrestris, the common earthworm known as a night-crawler, does nor survive in the compost pile but will enrich and aerate your garden beds. | Source


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 wriggler, Eisenia foetida, that is used for this purpose. Preferring organic matter over soil, they are voracious decomposers.

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 do NOT survive in compost piles, but will still benefit your raised beds and garden plots.

Both worms produce the mineral-rich castings that also 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.

Things you'll need to get started:

  • 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

Avoid meat, dairy products, and oily things in any composter. They will smell bad and attract rodents and flies. It's easy to keep a small container near your kitchen sink for collecting the appropriate waste to add later. Grass clippings and yard waste should be free of disease and pesticide residue. Red wigglers are usually available in garden centers or can be ordered on-line. A good information source for composting is Worms Eat My Garbage by Mary Appelhof.

  • 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 1-2 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! 2 lbs. 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

Earthworm castings are also available in most garden centers. 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!

Questions & Answers

    © 2011 Catherine Tally


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      • cat on a soapbox profile image

        Catherine Tally 23 months ago from Los Angeles

        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.

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        Shirlee 23 months ago

        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?

      • Fennelseed profile image

        Annie Fenn 6 years ago from Australia

        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.

        Great hub!!

      • cat on a soapbox profile image

        Catherine Tally 7 years ago from Los Angeles

        meghansmummy- I'm glad that I was able to teach you a new gardening trick. Thanks for following :>)

      • meghansmummy profile image

        meghansmummy 7 years ago

        wow i never knew that x

      • cat on a soapbox profile image

        Catherine Tally 7 years ago from Los Angeles

        Thanks, Alicia- It's a pleasure to help out a fellow gardener!

      • AliciaC profile image

        Linda Crampton 7 years ago from British Columbia, Canada

        I love the information and details in your hub. You've given great advice to gardeners!

      • cat on a soapbox profile image

        Catherine Tally 7 years ago from Los Angeles

        Thank you, Will!

      • WillStarr profile image

        WillStarr 7 years ago from Phoenix, Arizona

        Very informative and useful Hub.