5 Ways to Harvest Worm Castings

The ability to harvest small handfuls of worm castings as needed is a thing of composting beauty. However, in order to ensure that your vermicomposting system diverts the greatest volume of organic material and supports the healthiest worm population, it’s important to fully harvest and refresh the tray(s) every so often!

You will know that a harvest is on the horizon when bin contents have dropped substantially and the original bedding material is practically unrecognizable, having been replaced by brown, earthy vermicompost and castings. (For a distinction between the two yields, check out THIS POST)

When harvesting castings, the trick is to separate out and keep as many worms as possible. Any escapees won’t wreak havoc in your garden, but they are more likely to survive and thrive in the hospitable environment of the worm bin. Plus, red worms are ideally a one-time investment; a multi-generational family of worms will perpetually produce nutrient rich castings as long as they are kept in the bin!

There are a variety of ways to harvest worm castings. Here are a few of the most common methods:

(1)   MIGRATION METHOD
Worms will follow food scraps, and given a little time, can actually be guided to sort themselves from their castings. The key is to STOP feeding the area you wish to harvest, and ONLY add food to the area with fresh bedding. The worms will travel to the new area in search of food, leaving you with (virtually) worm-free castings to harvest. After harvesting, replenish the now-vacant side or tray with new bedding and food scraps to restart the process. Isn’t it nice when the worms do all the work?

There are two general ways to implement the migration method:

(1)      If your worm bin is comprised of a SINGLE TRAY, the worms will need to travel horizontally to one side of the bin. Move material to be harvested to one side of the bin, and replenish the other side with fresh bedding and food scraps.

(2)      If you want to utilize MULTIPLE TRAYS, the worms will need to travel vertically (either up or down) to a newly-prepared tray with fresh bedding and food scraps.

PRO: This easy, self-contained process is mostly hands-off; useful for anyone who is queasy about handling the worms or getting a little messy.
CON:  Expect waiting 1-4 weeks (depending on the size of the bin) for a good proportion of the worm population to relocate to their new home.

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(2)   PHOTOSENSITIVITY METHOD
Worms are highly sensitive to light, and will readily move away from light sources. By strategically introducing light, worms can be guided to burrow to a desired location, allowing for easy collection of the remaining castings. If outdoors, choose a sunny location to work; if indoors, place the piles under bright light for the entire process.

There are two general ways to implement the photosensitivity method:

(1)     The VOLCANO/CONE METHOD is practiced by emptying out the bin contents onto a stable surface (that you don’t mind getting dirty) and sorting the castings into loosely-packed, cone-shaped piles. The worms will continually burrow away from the edges to escape the light, allowing you to scrape the worm-free castings off of the tops and sides of the piles. Take a 15 minute break after each round of castings removal to allow worms time to move inward. Repeat this process several times until only small piles of worms and castings remain; these can be placed into a bin with fresh bedding and food scraps.

(2)     The BURLAP/FILTER METHOD is practiced by first emptying out bin contents into a temporary holding area, and immediately replenishing the empty bin with fresh bedding and food. Place a piece of damp loosely-knit burlap (or any mesh cloth with openings large enough for worms) over the bin allowing it to hang over all edges. Spread a thin (approx 1 inch) layer of castings on the burlap. Wait for at least 20 minutes for the worms to burrow away from the light source, directly into their new home. Worm-free castings can then be removed from the top of the burlap. Repeat this process until all bin contents have been separated.

PRO: Fairly organized and immediately gratifying processes that allow the harvester to multi-task.
CON:  Not for the easily distracted; worms that are left in the sun for too long will not survive the ordeal!

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(3)   FREE-FOR-ALL/MEDITATIVE METHOD
If you love getting to know your worms up close and personal, this slower-paced, hands-on style may just be the method for you.

There is essentially no planning or technique required with this method; simply dump out the bin contents (probably onto a surface you don’t mind getting dirty) and remove the worms from the castings by hand. Worms should soon after be placed into a bin or tray with fresh bedding and food scraps. While less organized than the other methods, this strategy is perfectly effective as long as you don’t mind spending a little extra time sorting through castings.

PRO: Immediately gratifying, lots of fun for those who enjoy handling the worms, and a great activity for kids!
CON:  Not a recommended method for the impatient or for those looking for a time-efficient technique.

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Happy Harvesting! 

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9 thoughts on “5 Ways to Harvest Worm Castings

  1. Love the burlap idea. I just spent half a day hand sorting the worms. Not looking forward to doing that again. I think I will try the burlap method next time. I sure hope it works. If it does, I will do that until my worm farm gets too large for that to be practical. Thanks for the tip.

  2. Thanks! I’m doing my first harvesting so this is very helpful in refreshing my memory. Also, this is a very nice quality post!

  3. I have been vermicomposting for a full year, using three Can o’ Worms bins. I estimate that I have between 5,000 and 10,000 red wiggler worms.

    Regardless of how ready-to-harvest the bins are, the worms refuse to leave them for fresh bins above or below. I have to nearly empty the harvesting bin and then aggressively agitate the castings every hour during daylight for a week in order to force worms to migrate, and even at this, they do not migrate willingly. It is the worst part of vermicomposting, and it has eroded my enthusiasm for composting considerably.

    In a full year, I have not filled even one plastic storage bin of castings. And the castings bin now is filled with worms, too, since baby worms, too small to see, were in the harvested castings.

  4. I have been vermicomposting about 4 years using large totes in which I drilled holes in the bottom. When I want to harvest castings, I remove the container cover, lay some window screen material over the open top and put the container in the sun. The worms quickly move down out of light and heat and I gently scrape off the layers of castings. I come back and do this multiple times a day for a couple of days and voila I have a 15 gal bucket of worm castings ready for the garden and a bunch of worms at the bottom of my container ready to start the process all over again. I found this method works better than putting all of the contents onto a tarp. First of all I couldn’t go off and leave my piles while the worms migrated inward because my chickens, etc would think they had been invited to a tasty party of worms:) The volcano method took way more “babysitting” than the method I described above. Good luck and enjoy!

  5. I use an office shredder to shred brown, label free, cardboard and brown paper. I use this for bedding.

    Does this make harvesting more difficult? Once I separate the worms, I’m left with a mixture of castings and soiled bedding.

    • The bedding you are using is great for vermicomposting. It shouldn’t create problems with harvesting since we use the disappearance of the paper/cardboard as an indicator that the compost is ready to harvest. When most of the bedding material is gone, stop feeding the bin. If you have stacking bins, prepare the worms a new,freshly made bin to use and allow the worms to slowly move to the new bin.Otherwise, check our website or come to a free workshop where we teach other harvesting methods.

    • I have used nothing but shredded, uncoated paper as bedding for my worms. The worms leave their castings on the top layer of shredded paper, and as it becomes completely covered, it decomposes and mixes into the finished product to harvest. I have moistened the paper before adding it to bins, and I’ve added the paper completely dry. The worms appear to enjoy shredded paper either way.

      If you are able to clearly distinguish the shredded paper from the castings, the material is not yet ready to harvest. Give the worms more time . . . an extra week to a month, depending upon how large a population you have.

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