Tina..remind me what kind of bin you have.

As SQH1 is alluding, the way you manage your bin will determine how you approach harvesting the castings. Systems that are top-fed, meaning feedstock is added to the system in thin layers spread over the bedding surface that are then covered with an equally thin layer of bedding material, are harvested when the bin is filled. The top few inches of material, which typically contains most but by no means all of the worms, is scooped out and set to one side, and the finished/mostly finished material beneath, which will contain some worms, is scooped out for use in the garden and on houseplants.

In pocket fed systems, which are bins that are filled to the top with dampened bedding and fed by dumping feedstock into pockets dug in the bedding, harvesting is accomplished using a variety of methods:

Dump and sort
This method involves dumping the whole of the bin contents onto a tarp beneath a bright light or, best, in the bright sun, and fomring the material into several cone-shaped mounds. Worms, being photophobic, will dive to the center of these mounds to avoid the light, allowing you to scrape off the vermicompost on the outside of each mound until the worms are again exposed. Continue scraping away the vermicompost from each mound until all that remains is a pile of worms. The worms can then be placed back in the freshly bedded bin and the vermicompost applied to garden and houseplants.

Forced screening (my personal favorite)
Usually used in pocket fed systems, forced screening ivolves operating the bin as normal until the original bedding is no longer recognizable and the total bin volume has decreased by at least half. At this point a piece of fiberglass window screan cut several inches larger than the surface area of the bin is laid on top of the bin contents. Lay the excess screen length flat against the inner bin walls, and fill the bin the rest of the way to the top with new, dampened bedding. Feed into the new bedding on top of the screen as you normally do. Younger worms will squeeze through the window screen to the new food source above once that feedstock becomes biologically active, while older, larger worms will remain beneath the screen to finish off all remaining feedstock. Once the food sources beneath the screen are exhausted or become less attractive than the nice-smelling feedstock above, the larger worms, too, will squeeze their way through to the top.

In the mean time, of course, you will have been simply feeding into the material on top of the screen. Once the material on top of the screen is ready for harvest, signified by the bedding being no longer recognizable and the volume of material on top of the screen decreasing by roughly half, grab the excess screen length along the inner walls of the bin and lift it and the material on top of it (which will contain the vast majority of the worms) out of the bin. Dump the finished material from the bottom of the bin, which will contain a few worms, for use in the garden and on houseplants, and dump the material from on top of the screen into the bottom of the now empty bin. Lay the same piece of screen on top of the material with the excess length pressed flat agains the inner walls, rebed with new, dampened bedding, and feed into the bedding on top of the screen as you did before. The process now begins again.

The bright folks who participate here have developed fascinating and effective variations to each of these harvesting methods as well as some unique methods I've not mentioned here, and hopefully they will share their ideas with you, but this is a beginning on bin harvesting options.

Some important thing to keep in mind:
1) When you harvest you are highly unlikely to remove all of the worms from the finished material. There is no problem with this! The number of worms lost will have no measurable impact on the processing rate of the newly set up bin, and the worms remaining in the finished material will have no negative impact on your garden. Neither will the worms remaining in the finished material when it is applied to the garden be sentenced to death, as so many other internet fora erroneously claim. The types of worms used in worm bins are found naturally in soils throughout nature. They did not evolve in the bins of neanderthal man, but in the soil, millions of years before man appeared on this little planet to build them bins, and they will continue to live there as nature intended should they be introduced to your garden in your finished vermicompost.

2) The finished material from your bin is not pure worm castings, and neither is it necessary or even advantageous that it is. The finished product from a worm bin is vermicompost, defined as a mixture of worm castings (typically about 80% or so), decomposed OM that did not pass through the gut of the worm, and small bits of undecomposed material. Research shows that vermicompost produces excellent plant growth response, and, in many/most cases, better response than does pure castings (achieved by screening the material).

Ok, this is rather long-winded, so I'll close here, hoping that you will continue to ask questions should you still have them, and looking forward to the responses of the other wise and creative forum participants, though you should watch out for posts by Chuckie. He sometimes sees aliens in his worm bins.....

KellyS

Kelly and all,

After reading this VERY informative topic, I have a question. Supposing you have a 10 gallon setup, and are using the pocket feeding/screening method, what is the turn-around time for harvesting? I know it is going to depend on heavily stocked your setup is, but can you give us an idea what to expect?

Karen :)

Karen, most likely nobody can tell you how fast your worms will process your feedstock. As much as its a matter of worm population, its also determined by what you're feeding your worms. Fruit pulp and tomato leavings decompose much faster than potato and onion peelings. And its the speed of decomposition that determines how much food is available to the worms.

That said, my rubbermaid bin with a variety of food would take 4 to 6 months to be busting for a harvest. Except that I recently split the population into two bins and its slowed down. So, as they say on TV, your milage may vary...

Oh, and Kelly forgot about the six pack method of harvesting. No waiting for migration, no standing out in the sun scaring the poor worms into hiding, just you and your worm buddies mellowing out in the shade while you sift them through your fingertips. A simple, thorough, mindless excuse to drink good beer while saying "yeah, but I'm getting something done."

Is there a time when you stop feeding them kitchen scraps and let the worms finish turning the remaining bedding, etc. into castings?

I have a 14 gal tub that is about 1/2 fill of castings and bedding all mixed together. I used to do the pocket feed but lately just throwing a little on top now and then. Worms are doing great and making babies like crazy! Can the worms and babies continue to live on the remaining remnants of scraps and bedding?
:)
Tina

I don't stop feeding before harvest, Tina. But when harvesting by hand, I just toss the partially decomposed stuff into my bucket of reclaimed worms to go back into the bin. I have small bits of undecomposed stuff when I'm done, but it doesn't bother me.

The worms that I didn't recover continue to process the compost in the wife's "houseplant bucket" until the poop goes into the flower pots.

This works well in my very small scale operation. For other situations, listen to the others. :)

Tina..If you stop feeding the bin, the worms will finish it off..but you will start to lose your population. You could nest another bin (set up the same as your first), inside your first bin. Stop feeding the lower bin. Put your fresh food and bedding in the new, upper bin. The worms will migrate up to the fresh food. (Kelly has a screen method that is great too.) Either of these ways will allow your population to grow and your compost to finish off more.

SQH1,

What size holes would you make in the upper bin so that they can migrate upwards and how many holes would you recommend?

:)

Thanks everybody!

Tina

I would put the same amount of holes as your other bin..assuming you have holes in the bottom of your working bin. In my 10 gallon rubbermaids, I put about 24 1/4" holes. Make sure the bottom of your second bin is in good contact with the compost in your first bin. Worms aren't good jumpers..:)

Thanks everybody!

:)
Tina