How to Harvest Worm Castings from a Simple Worm Compost Bin
Worm castings, also known as “black gold”, are a stellar natural fertilizer for your garden! They provide rich, readily-available nutrients for your plants, and improve your soil structure too. Maybe you know this already… Possibly, you already have a worm bin – and have been diverting your food waste into it. Good for you! Now you just want to know how to harvest the worm castings, so you can put them to good use. Let me show you how!
When the time is right, harvesting worm castings from a basic worm bin is really, really simple! And I have a few tips to make it even easier! The worm castings can be sifted with a DIY screen system, as I will show you in the demonstration video at the end of this post. Or, they can just be harvested by hand.
This post is geared for folks using a simple tote-style, single-compartment worm bin like we use. The fancier layered worm bins have their own harvesting methods.
If you don’t yet have a worm bin at home and are interested in getting one set up, or need some pointers to help better maintain yours, check out this post to learn just how easy it is! Vermicomposting 101: How to Create & Maintain a Simple Worm Bin.
Preparing your Worm Bin for Harvest
If you just created a worm compost bin, don’t expect castings to be ready for harvest immediately. The worm bin needs to get established, and be routinely fed and fluffed for a few months first. This gives the worms time to eat, turn things over, and break down food and bedding into worm castings – their poop.
Once you begin to see the worm bin transforming from raw materials into finished worm castings, you can think about harvesting them. Finished worm castings look similar to good, rich soil. They’re dark brown, tiny, round bits of material that have passed through their system.
When harvesting worm castings, the goal is to collect as much castings as possible, but leave the worms behind in the bin. It is okay if a few worms come along for the ride, and some of their egg cocoons and tiny babies will inevitably be harvested. That’s fine! On the other hand, you don’t want to deplete your worm bin population by removing too many. Therefore, we need the worms to get out of the way!
Move Over, Worms!
A week or two before you want to harvest the worm castings, stir and spread the contents of your bin out in the bottom. Next, feed the worms exclusively on one side of the worm bin during that time. Bury the food (and if needed, any new browns/bedding) in one far corner, with plans to harvest worm castings from the opposite side. The worms should migrate there to eat, leaving the other side of the bin hopefully worm-free. If there is a lot of existing food matter and worms spread evenly throughout your worm bin, it may take a little longer to accomplish this.
Once the majority of the worms have migrated, it is time to harvest castings!
Harvesting Worm Castings
One extremely simple method of harvesting worm castings is by scooping them out. Using a small trowel, scoop out the finished castings from the “resting” side of your worm bin into a bucket. That’s it!
However, depending on how well broken-down the material in your worm bin is, or how well the worms migrated to the opposite side of the bin, you may need to pick through the material a little by hand. Sift through the castings and throw back large pieces of food matter, lumps of shredded paper or other bedding, and as many worms as you reasonably can. If the worm castings are clumpy, try to break up the large chunks.
Another option is to take it one step further – to harvest and then sift them with the aid of a simple screen.
Screening Worm Castings
We used to just scoop and pick through castings with a trowel, as described above. It took fewer “tools” to sift by hand, but honestly, it took a little longer and more effort than the method I will describe next.
A couple years ago, Aaron attached some hardware cloth to scrap wood for another project he was working on. It just so happened that it made an absolutely perfect worm castings screen! It consists of a wood frame with half-inch hardware cloth over it, attached using wide flat-head cabinet screws. Heavy-duty staples would work as well.
We used 2×6” wood pieces because that is what we always have on hand (scraps from building raised garden beds!), but any size lumber pieces would work. A bamboo stake supports our screen on the more open side of it, but you could totally make a four-sided wood frame instead. Clearly, it’s nothing fancy.
Place the screen frame on top of a plastic tote or other container that will catch the screened worm castings. Dump some on, push it around to sift it, and let the worm castings fall through. Repeat as needed until all of it is sifted and separated. I use my hands, but you could also use a trowel.
The holes in half inch hardware cloth seem perfect for the job! The resulting screened worm castings are nice and fluffy, with any large chunks broken up. Large bits of matter are easily caught by the screen, and can be put back into the worm bin. Worms may get through the screen, or may stay on top. Either way, you should be able to easily see and sort them.
Voilà!
Now you have finished, fluffy, ready-to-use, perfectly harvested worm poop.
How to Use Worm Castings
If you’re wondering “what do I do with worm castings?”, the answer is: SO MANY THINGS! Add the castings directly to your raised garden beds or other garden soil as a rich natural fertilizer. They also help to improve soil aeration, drainage, and moisture retention. We like to add a little handful to every planting hole when we are transplanting new seedlings outside. Also, worm castings are a great addition to seedling start mix when you’re starting plants from seed. Put a few scoops around the base of fruit trees. Or, give your houseplants a special treat!
One of the great things about worm castings is that a little goes a long way! By using even a small amount in your garden, you’ll see the difference. On the other hand, you really can’t “overdo it”! They are not “hot” like other fertilizers. Meaning, worm poop cannot burn or shock your plants. In my humble opinion, the more the merrier.
One of our absolute favorite ways to use worm castings is to make actively aerated compost tea (AACT) with them. Check out this post all about how to make AACT!
We try to add castings to our garden in every way possible. If you do the same, I promise your garden and plants will thank you tremendously for your effort!
Check out this demonstration video to see just how quick and easy harvesting and screening worm castings can be!
See? Easy peasy.
I hope you found this post helpful in your vermicomposting journey! Please feel free to ask questions, and spread the love by sharing this post.
44 Comments
Rebecca Kalinchuk
i bought the commercial layered worm bin 2 years ago, bought Uncle Jim’s red wigglers and enjoyed feeding them with my daughter. however at some point as we were adding new layers, it seemed the worms died, there were still worms but not that many – certainly not as many as when we bought them. What did we do wrong? we live in north WA so kept the bins inside the house. temp shouldnt have been an issue. Air circulation? we kept them fed and followed the rules on food.
Aaron (Mr. DeannaCat)
Hi Rebecca, I am not familiar with the worm bin you used for your worms but typically if the worms start to reduce in numbers, their environment wasn’t right for their survival. The bedding material was likely either too wet or too dry as that is typically the culprit for an unhappy worm bin. As long as there were still some worms left, they would repopulate themselves in time if their environment was corrected. Worms will also limit or expand their population depending on how much space and food they have. They will continue to reproduce if they are getting enough food and they have the room to expand. Hope that helps and reach out if you have any other questions, good luck!
Jennifer
Do you “fluff” your worm bed? I have seen some advise to “fluff” (to aerate) and others advise not to disturb. I’ve only had my worms three months now, and I still don’t know the right thing to do. I do tend to move the bedding around quite a bit in the upper part of the bin when feeding, but I have also dug down enough to see that the bottom of my bin is more compacted than what yours appears to be in the video where you are harvesting the fluffy and loose castings from the bottom of the bin. I don’t have any confidence at all that I will even know when the castings are ready to be harvested. I feel stupid, because it all just looks like “dirt” to me. 🙁
I do think my worms are doing okay. My worm bin seems to be doing well (smells good, moisture seems great–at least where I’ve “fluffed”–but obviously wetter down at the bottom where the bedding is more compacted). If you have any advice as to whether or not I should be “fluffing” the worm bedding (and to what depth to do it), I would appreciate it. I also would appreciate any advice on knowing when the castings are done, because–as I said–it all just looks like “dirt” to me. But my bins are only three months old right now, and I’ve read (maybe on Uncle Jim’s site) that you shoudln’t harvest any sooner than three months anyway.
Thanks for any advice you may have. I attribute the success of my worm bin so far to having followed your instructions and advice on the setup and maintenance of them. I’m just a little confused now that I’m getting closer to the point of being able to harvest the castings.
Aaron (Mr. DeannaCat)
Hi Jennifer, so glad to hear you are having success vermicomposting even if a few things are still “fuzzy” to you. As far as fluffing your worm bin, we like to do this on occasion, we don’t really keep track of how often but once a month is likely more than often enough to keep things nice and aerated so the material on the bottom won’t get too wet or anaerobic.
When to harvest castings may take a little experience but if you just started your bin three months ago, I would think you are on the very early end of harvesting the castings but I would likely just let your bin continue to grow unless you need the castings for something in particular. We will take out small amounts here and there but usually do a heavy harvest once a year when our bin starts getting too full where we will go through and harvest a lot of the castings while also separating the worms out to throw back in the bin. Just look up what worm castings look like if you can’t tell well enough from the photos we included in the article but they also feel much different than regular dirt as well.
Anyway, it seems like you are doing everything right so just keep up the good work and you should be able to harvest some castings before too long. Hope that helps and good luck!
Jennifer
Thank you! Yes, I knew I was on the early end of of being able to harvest any castings, so I will be more patient and rest assured that I will be able to recognize the castings as things progress further. I cannot thank you enough for the simple instructions for how to begin a worm bin. I ready so many different options, and yours is the one that felt the most approachable (and affordable) to me. I do think things are going well and, as I said, I attribute that to the great instruction and information from your website. You make it simple and approachable. I really appreciate that. Thanks again for your reply. 🙂
Aaron (Mr. DeannaCat)
Hi Jennifer, thank you so much for the kind words and we are happy that you found our information so approachable, have fun vermicomposting!
Sara
Hi! Thanks for the helpful information on vermicompositing. I constructed a worm bin like yours a little over a year ago and I have a TON of worms! The problem is I’m having difficulty harvesting castings because the bin material is a bit too clumpy/wet. The bin doesn’t have a foul odor so it’s not terribly out of balance but enough so that the castings clump together too much to harvest. I’ve added a lot of shredded newspaper a few times to absorb moisture, and on top of that, I always add newspaper bedding whenever I feed them. Any suggestions for how to correct this problem?
Aaron (Mr. DeannaCat)
Hi Sara, it’s great to hear you have been successfully vermicomposting for over a year now and everything seems to be going well! The worm castings can stick together and be somewhat clumpy in general but we like to use a compost type screen that we made to harvest worm castings. It helps break down the castings as they sift through the screen, it also helps with being able to pick the worms out of the harvested castings to keep them in the worm bin. Check out our article on How to Harvest Worm Castings from a Simple Worm Compost Bin for some ideas that you may find useful. Hope that helps and have fun vermicomposting!
Melissa
Thank you so much for sharing this info. You’ve inspired me to try it! Question: after you harvest the castings, do you need to add more “bedding” material to the bin? Do you add bedding materials on a regular basis as well… or just the veggie scraps? Thank you!
Aaron (Mr. DeannaCat)
Hi Melissa, you don’t always have to add more bedding with every feeding but it is typically recommended, the bedding are the “browns” to the “greens” of the food waste. Too much food stuffs can make the bin turn too wet and make it go anaerobic, with time, you get the hang of what the compost should look like and if it is too wet or too dry but it is best to have a little of both. Hope that helps and have fun!
Brandy
Newbie to vermicomposting but long time reader of your blog with a potentially dumb question… does the ink on the newspaper matter?
Aaron (Mr. DeannaCat)
Hi Brandy, it’s great to hear you are going to be getting into vermicomposting and thank you so much for your support of Homestead and Chill! The ink on newspaper doesn’t matter as most of it is non-toxic, soy or water based ink along with some pigments and waxes, you just don’t want to use glossy paper that is typically found in magazines. Hope that helps and have fun venturing into composting with worms!
Yoram
If nessessary, what is the best way to store ready to use vermicompost? and also, can it be harmful, damaged or lose quality, as result of prolonged storage? How long does it take to stored vermicompost after being harvested befor it gets spoiled (if it does at all) ?
Thanks for the exellent guidance.
Aaron (Mr. DeannaCat)
Hi Yoram, we store extra vermicompost in storage containers or even 5 gallon buckets with lids. It can be stored for quite awhile this way, you just don’t want it to dry out so keeping a lid on it will help it contain its moisture. It can get a little smelly if you leave it for too long, especially so if your castings were more wet to begin with, we typically don’t store castings for much longer than a month as it isn’t necessary for us. If you did need a longer storage time, maybe construct a tote, similar to a worm bin with a few air holes to store your excess vermicompost. Hope that helps and good luck!
Lynda
My question is:
Will some worms be inevitablly killed in the process of sifting their castings and/ or making the tea?
Thanks
Lynda
Aaron (Mr. DeannaCat)
Hi Lynda, I can’t say for sure but when I sift the vermicompost, I pick out the worms as I see them and add them back to the worm bin. We have also seen worms that have ended up in the compost tea and they are still alive after the 48 hours of bubbling. They will likely invariably end up in your soil (as even their cocoons (eggs) will be in the compost) and you can also add the extra compost back into your bin. Hope that helps and good luck!
Phil
1/2″ hardware cloth? Holes seem a bit big. I would go down to 1/4″ holes at least. I use a screener that has even smaller holes. Tedious and time consuming? Yes, but nothing but castings and maybe eggs.
Aaron (Mr. DeannaCat)
Hi Phil, we usually have 1/2″ hardware cloth around so that is what we used to make the screen. It still does a great job and we end up with really nice castings without much else as we typically harvest parts of the bin that haven’t had any food scraps in a number of weeks.
Kristel
I just started my worm composting bin. How do I know when it is ready to harvest some?
Aaron (Mr. DeannaCat)
Hi Kristel, it will still likely be a few months out but as your worm bin matures, you will see the material turn into worm castings as the bedding material is consumed. Our worm bin now is mostly all castings with shredded newspaper/cardboard as bedding material mixed in (along with food scraps) and we will typically let the bin fill up to a point where we just harvest a good portion of most of the castings at one time. Hope that helps and good luck!
jim purdy
Plenty of interesting ‘worm talk’. We keep our Reds in a bath tub which will soon be on wheels….I didn’t see anything about temperature. What is the ideal temp. for them? We live upnorth but we have reasonable priced electricity for heat.
JP
Aaron (Mr. DeannaCat)
Hi JP, the optimal temperature for red wrigglers is between 57 and 77 degrees Fahrenheit.