Worm Castings: A Gardener's Secret to Success

Worm poop is a gardener's gold.

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Drip-line diagram:

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What are worm castings? Simply put, they are worm poop. It may sound bad, but castings actually have no offensive odor and a very neutral pH. 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.

Benefits of worm castings:

Worm castings contain primarily humus which helps to remove toxins 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 micronutrients 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 verticilium wilt, a common disease of tomatoes.

Another impressive benefit is the natural resistance to insect infestation. 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 act as a natural insect repellant. If a bug feeds on the leaves of a plant which has absorbed the chitinase, its stomach will soon begin to dissolve, and death will come quickly. I especially recommend applications against the most stubborn sapsuckers like ahpids, thrips, whiteflies, mealybugs, and mites. An application of worm castings should be about 1" thick and a foot or so in width. Spread it around the drip line of the tree or shrub and cover with 2" of compost. Castings can also be mixed 1c per gallon of water as a brewed tea then applied as folliar spray.

At times when plants are heat or drought stressed or in a general state of decreased vigor, I prefer to NOT use fertilizer until the specimen begins to show some recovery. Imagine being asked to run a mile when you've got the flu! Worm castings, on the other hand, add nutrients which improve health without forcing a plant into leaf or flower production. Using them to nurse a plant back to health is a good strategy.

In areas where soil is dusty and unable to absorb water, plants suffer because moisture never makes it to the roots. I live with this in my own garden, and it is an ongoing challenge! After many years of expensive trial and error, I've finally found a solution! I mix topsoil, compost, and worm castings in equal parts and work it into my existing soil twice a year: in early Spring and late Fall. I also save my leaves and spread them for a nice mulch. This keeps the worms active and provides shelter for my lizards, providing both natural soil conditioning and pest control.

Earthworm castings are available in most garden centers. Some varieties have added minerals and nutrients as well as increased levels of chitinase. Castings can also be harvested at home from the red worms in composters. In a stacked bin, the castings will often filter into the bottom tray. The best way to collect castings from home composters, is with a steel mesh screen. Some devices are rotating and will allow the compost and worms to drop off into an end bin while the castings filter into a bottom tray.

The red wriggler is used for composting.

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

Common earthworms aerate the soil.

Lumbricus terrestris, the common earthworm, does nor survive in the compost pile but will enrich and aerate your garden beds.
Lumbricus terrestris, the common earthworm, does nor survive in the compost pile but will enrich and aerate your garden beds. | Source

Stacked worm bins make the process easy for beginners.

Do it yourself:

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 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.



Worms can be raised in a bin or a special worm habitat, preferably wood or plastic with good aeration. The main necessities would be bedding like shredded newspaper,leaves, straw, cardboard, or coir. The bedding layer needs to be kept evenly moist, not soggy, like a wrung-out sponge. On top of the bedding layer, put a layer of soil, then compost and organic garbage like tea bags, coffee grounds,crushed eggshells, and veggie/fruit peels and scraps. ( 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. Ideally, 2lbs. of worms to a pound of compost is a good way to start. A great source of info on composting is Worms Eat My Garbage by Mary Appelhof.


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. You will not be disappointed. Happy harvest!

Consider a more sustainable approach to the garden.

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© 2011 Catherine Tally

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Comments 9 comments

WillStarr profile image

WillStarr 5 years ago from Phoenix, Arizona

Very informative and useful Hub.


cat on a soapbox profile image

cat on a soapbox 5 years ago from Los Angeles Author

Thank you, Will!


AliciaC profile image

AliciaC 5 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

cat on a soapbox 5 years ago from Los Angeles Author

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


meghansmummy profile image

meghansmummy 5 years ago

wow i never knew that x


cat on a soapbox profile image

cat on a soapbox 5 years ago from Los Angeles Author

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


Fennelseed profile image

Fennelseed 5 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!!


Shirlee 6 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?


cat on a soapbox profile image

cat on a soapbox 6 months ago from Los Angeles Author

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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