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Harvesting Worm Castings

dozen wormsWhen you have a vermicomposting system, you periodically need to harvest your worm castings. This nutrient-rich “black gold” is the perfect fertilizer for your plants. Harvesting also helps keep the worms healthy. You will know it is time to harvest when most of your worm bedding has been turned into a rich, dark, soil-like substance of vermicompost and castings.

There are several good methods for harvesting worm castings for small home-based vermicomposting bins. Which method you choose will depend on the type of system you have set up, and on your personal taste.


There are single tray vermicomposting systems, stackable multi-tray systems and many do-it-yourself systems. Choose a method that efficiently extracts the casting while leaving enough worms behind to keep composting.

Method One: Encourage Worm Relocation

A very popular method for harvesting, the worm relocation method is based on the fact that worms will migrate towards food. In a single tray system, gather whatever uncomposted scraps remain in the castings and move them to one side of the tray, or to the center. Add fresh food only in the spot you want the worms. In a multi-tray vermicomposting system, put food in the tray above the one you want to harvest. In a matter of one to four weeks, depending on the size of the tray, most of the worms will naturally migrate to the food source. This will leave you with nearly worm-free castings to harvest. At this point, you can also fish out any remaining eggs, which are small and yellow, and will yield more worms in the future. This method is great for anyone who feels squeamish about touching worms.

Method Two: Relocation by Light

Worms will automatically move away from light, so applying artificial light or sunlight to your castings can also yield worm-free castings. Caution: Never expose your worms to excessive sunlight or heat, or they may dry up and die.

You can try one of two things:

  • Gently dump out your worm tray on to a clean, stable surface and build mounds of castings. In about twenty minutes, the worms will burrow down to the bottom and away from the sides to escape the light. You can then scrape off the tops and sides of the pile, working in, until only small piles remains. Or,
  • Gently put the worm castings into a temporary holding container. Add more food and bedding to the now-empty worm tray. Take a piece of burlap or other material with worm-sized holes and drape it over the worm tray. Spread a thin layer of castings and worms, 1-2 inches thick, over the cloth and wait twenty minutes. By then, the worms will have burrowed down into the worm tray. Put the worm-free castings into a storage container, and apply them to your plants’ soil.
    Note: Instead of burlap, you can construct your own filtering trays using wire mesh. This method must be done in a timely fashion so that the worms can stay damp. Both sunlight and human hands can dry out worms, which can harm them.

Method Three: Hand Harvest

For those who are willing to do things at a slower, more intimate pace or who, only need a few handfuls of castings right at the moment, this method may be desirable. Simplest of all, it only requires gathering up handfuls of castings and sifting through them for worms which can then be placed back in the tray. You can dump out the whole tray at once and reload it with food bedding and sort through it all. Or you can choose just a few handfuls if it is not an appropriate moment for a full harvest. Children often enjoy the fun of this kind of sorting.

Method Four: Screen Compost

Sift the worm bedding through a screen and you will separate the worms, sticks, and undigested material from the finished compost easily. Screened compost is especially valued because it’s light and fluffy, and free of debris. You can buy or make a composting screen. See our instructions for screening compost.

After your worm castings are harvested, they can be stored in a sack, clean bucket or other container until you are ready to use them. They are teaming with healthy soil bacteria and nutrients that are perfect for adding to soil. Help your plants and lawn grow strong, and keep your worm population happy by harvesting worm castings regularly.


Note: If you need more composting worms, just order worms online from Uncle Jim’s Worm Farm. We have been in the worm business for more than 25 years, so we must be doing something right! They are guaranteed to arrive alive or we will replace them.

11 comments on “Harvesting Worm Castings

  • i have been looking on the net to find the answer to this question. How long do worm casting last? In other words, is there a shelf life? How long roughly? I have filled a 5 gallon bucket and its mid November now. Will they last till spring?

    thanks Uncle Jim,

    sincerely Adam Cooper

    • Hi Adam,

      The compost can last indefinitely. However, once dried out, the microbes that are throughout the compost will not last. You will want to use it as soon as possible to utilize all of it’s benefits. Have a great day!

      • I have the same question. I have castings ready to harvest now in December. But how can I keep them without loosing the nutrients? Can I put them in the garden under mulch when it’s snowy?
        Thank you.

  • I accidentally mixed in shredded credit cards in with my paper. I though I picked it all out, but there is still some left in my work castings. What can I do to separate the soil from the plastic strips?
    Thank you.

  • I use the stacked tray system. I have successfully harvested the bottom tray while the worms are “dining” in the upper trays. I mixed my harvest in my potting soil but have tiny tomato plants coming up in abundance. I guess the solution is no tomatoes?

  • magnificent post, ery informative. I wonder why the
    other experts of this sector do not notice this.
    You shluld proceed your writing. I’m sure, you’ve a huge readers’ base already!

  • I’m new to this and plan to raise worms for fishing not composting but I would like to understand “Casting”/worm po which I can use as ferterlizer. I have a 32 qt container with about 4″ of peat moss. How long after I put my red worms in can I harvest the castings. Where are the casting found (on top, middle, or bottom of my peat moss). Do I just pour all my peat moss and worms in my 32 qt container in to my 1/4″ and 1/8” screen and all that’s not collected as either worms or eggs are considered casting, and then add all new peat moss???

  • Hal Meadows says:

    OK, I received 20 pounds of worm casting along with some tomato food, although I ordered ROSE food with expensive roses due at any moment! No instruction about how to use the worm poop ! What do I do….?

    Hal Meadows

  • Harvesting from a multilayer system using the screen method. When I filter through the screen and I can see hundreds of teenie tiny baby worms (Yay!) but how do I filter the baby worms from the castings? They are so tiny they go right through the screen! Thinking I’ll put the castings in a bucket, shine light to make all the babies go to the bottom and then just take off the top layer as readily available for use? Thoughts?

  • I have the “Squirm Firm Worm Factory 360”. It is a “self-sorting upward migrating system” of trays. I have all trays finally going, after several months of adding food, thus filling trays, then adding a tray with new bedding and food to draw the worms upward. I went to “harvest” my first tray, the bottom one as per instructions, and it looks like dry bedding with some egg shells. I am not seeing anything in that bottom tray that looks like “black gold”. Oh, and did I mention it is dry. Very dry. What do you suggest?


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