Some time ago we published our article: “Setting up and Managing Your Urbalive for Worm Composting Success”. While we did offer some information that would be helpful for anyone using a stacking system, it was, as the name suggests, mainly focused on the Urbalive Stacking Worm Farm.
In this article, we’d like to explore the topic of stacking systems from a broader perspective, hopefully helping to answer some of the common questions people have, and clear up some of the confusion about this very popular category of worm bins.
A lot has changed since the “early days” of stacking systems - when there might have one or two main options available (e.g. Can-O-Worms). These days, the number of makes and models and sizes and colours is almost overwhelming! Unfortunately, all these choices don’t necessarily mean we have better options than the “good ol days”. If anything, the glut of new manufacturers has led to a decline in the quality of these systems (on average), and often more of a focus on visual appeal than on successful worm composting.
Here at Pacific Composting, we’ve tested 7 different stacking bin models already - including some of the most popular ones on the market - so we like to think that we’ve got a pretty good handle on the topic 😉. That said, this isn’t intended as a stacking system brand review (although we may consider putting together that type of article at some point in the future).
OK let’s get the ball rolling with some basic PROS and CONS of stacking systems:
Stacking System PROS
- Tend to be lightweight (easy to move around).
- Don’t take up much space.
- Often quite attractive (by worm bin standards)
- Many models are quite affordable compared to other options.
- Designed for a “continuous-flow” process.
- Allow for drainage.
Stacking System CONS
- Most of them are made from plastic - resulting in reduced airflow and excess moisture retention. Cheaper models may not put up with much wear and tear.
- Wooden models tend to dry out too quickly and break down over time
- Tray volume is almost always too small for highly effective vermicomposting
- Small capacity and wet conditions can increase pest (and other) issues
- Although technically “continuous flow”, worm migration tends to be less than perfect
Bottom-line - stacking systems can offer a solid entry-level worm bin option, especially in cases where space constraints and aesthetics are important (e.g. in an office or classroom setting), but - ironically enough - proper management can actually be somewhat more challenging for beginners, given the small size of the trays (most models).
Some Misguided Ideas about Stacking Systems
There is a lot of misunderstanding when it comes to the use of this type of worm bin. Some of it simply comes from poor advice shared online (that gets passed around for whatever reason). Some of it unfortunately seems to come directly from the stacking bin manufacturers themselves. Either way, we hope to clear up some of the misconceptions about these systems.
All Trays Getting Started At Once
Often, it is a stacking system's total volume that is emphasized as a selling point, not the volume of each tray. Sometimes you will even see estimates of the total worm population size the entire system can supposedly support. Both of these stats can be misleading since these systems should only ever be started with a single tray, and it’s unlikely that you will ever have all trays operating (at full capacity) at once.
Some beginners end up under the impression that they should set up all of their trays at once. Unfortunately, this completely defeats the purpose of the stacking tray, upward migration, design. To add insult to injury, actually managing a system like this would be very frustrating, since you would need to separate the trays regularly just to add more food and habitat materials.
Our advice is to start with a working single tray, containing a small-to-medium sized population of worms (we’ll come back to this), and then gradually work your way upwards - with new trays being added only once the previous tray is quite full of well-processed material.
Stacking Order/Timing Uncertainty
Somewhat related to the last one, people can end up unsure of where, and (even more often) when to add new trays to their stacking system.
As touched on, all stacking systems are designed for the upward migration of composting worms, so the newest tray should always be the uppermost tray. Some of the confusion relating to this may come from one exception to the rule, relating to harvesting your vermicast. We will come back to this further along.
Regarding the timing of adding new trays, we recommend taking your time with this. It’s easy to assume your tray is “full” when the level of habitat materials and food are up close to the lip of the tray, but it is the overall level of finished material that you should be focusing on. This is the dark, (hopefully) rich-smelling compost that accumulates over time thanks to the activity of the worms and microorganisms. Once the level of this material occupies about ¾ the volume of the tray, you can start thinking about adding a new tray.
NOTE: You should expect to wait at least a month or two before getting to this point, but various factors can slow this down even further (e.g. cool temperatures).
Stacking Bin Leachate is the Same Thing as Compost Tea
Perhaps the most widely-spread, hotly-debated topic relating to stacking systems is the value of the drainage leachate. Once again, manufacturer marketing, and even the very design of the systems, seems to be at the heart of this one.
Many feel the liquid that collects in the reservoir (and can usually be removed via a spigot) is basically the same thing as worm castings tea. Many others take a completely opposing view, saying this a harmful leachate that should never be used on plants.
What is our stance on this matter?
It depends. 😜
We prefer a more middle-of-the road position overall, since there are a variety of factors that can determine what sort of liquid you end up with in your reservoir.
One major factor is simply the age of the system.
Early on, most of the leachate comes from liquids released from decomposing food materials. It will be very unstable (lots of microbial “food” left in it), and will become anaerobic much more quickly. This “young” leachate can easily end up with phytotoxic (plant harmful) compounds in it, and should be used very cautiously (if at all) in your garden - and never in potted plants.
Generally, the more mature the material in the lowermost tray (and the system as a whole) is, the greater the chance of you ending up with a liquid that can be used as a form of compost tea. If it is dark in appearance, and has a somewhat earthy smell or no smell at all, there is a decent chance it has some of the qualities we’re looking for.
We recommend always treating even this (mature) liquid with at least some caution, though. Diluting it at least 50/50 with rain water or aged tap water before use should help you avoid any potential issues, and you may still be best to avoid using it on potted and sensitive plants.
Some important points to keep in mind:
- It is extremely unlikely that leachate tea will ever be the same quality as a tea made from top notch, finished worm castings. So, we recommend focusing more on the production of quality vermicast, than on filling your reservoir.
- Speaking of which, some people suggest you should literally pour water through your stacking system to create more “tea”. This isn’t a good idea for a number of reasons. For starters, you’ll likely end up impeding the vermicomposting process by making conditions excessively wet (reducing airflow). You will further reduce the quality of your end product by leaching out beneficial compounds. Lastly, there is a good chance that an even higher number of worms will feel inclined to move and/or remain lower in the system.
Bottom-line: there’s no need to toss the baby with the leachate water 😜, but caution is warranted, and it’s always important to remember that not all leachate is created equal (not even close)!
Ending up with No Leachate is a “Bad” Thing
This one is very closely related to the last misconception, but is worth including on its own, since it seems to be a common concern among new stacking system owners. Considering everything we shared in the last section it’s probably not too surprising that people feel this way - but, rest assured, ending up with little to no leachate in your reservoir more than likely isn’t a bad thing!
We won’t go so far as to say that a dry reservoir is necessarily a “good” thing, since in some cases this may be a symptom of a system that is running too dry, but ending up with less leachate can actually be a sign of good moisture-management.
Once again, our big recommendation is to focus more on producing quality vermicast (that can then be used to make better quality tea) than on filling your reservoir!
Stacking System Start-Up & Harvesting
Two other stacking system stages that seem to cause confusion are start-up and harvesting. Let’s now look at each of them in more detail.
Starting Your First Tray
We’ve established that you should be starting only one tray at a time. Starting that tray properly isn’t necessarily the easiest thing to accomplish. There are a few factors aren’t working in our favour: 1) most stacking system trays have a very small volume compared to a regular worm bin, 2) trays have a lot of bottom openings that worms can crawl through, and 3) a lot of stacking systems have fairly poor airflow.
Short of drilling holes in the lid and sides (which is an option), there isn’t really much we can do about #3 (but hopefully stacking bin designers take this to heart and consider adding wall vents in future designs), but there are steps we can take to help with #1 & #2.
Something we always recommend when starting your first tray (note the emphasis) is to line the bottom with dampened newsprint or (even better) kraft paper. This helps to keep things nicely contained, and greatly reduces the chances of you ending up with worms down in your reservoir.
IMPORTANT: The lowermost tray is the only tray you will ever line with paper (obviously it would be counterproductive to block worm migration into upper trays)!
Next, focus on creating your “worm zone”. This is made up of the habitat and food materials that will occupy most of the volume of your tray. With bigger (i.e. non-stacking) systems, layering in your materials works fine, but given the small volume of most stacking bin trays, we suggest actually making a mix in a separate tray or tub and then adding it to your tray.
Aim for a ratio of 70-80% safe habitat materials (bedding / “living material”) to 20-30% food materials. Many stacking systems include a coir brick as a bedding option. If you hydrate/rinse this you will have a good starting place for your habitat mix.
We recommend using a variety of different habitat materials, ideally offering complementary structural and water-holding characteristics. A bedding mix that has worked well for us is 40% coco coir, 40% shredded cardboard and 20% hemp tow, but there are many materials and combinations that can work well. As alluded to above, we highly recommend including some form of “living material” in your mix, if at all possible, since this can greatly boost your population of beneficial microorganisms. These will in turn help to kickstart the decomposition process and make your worms feel more at home.
Mix and moisten all your materials together before adding them to your tray, making sure to leave some space for your cover bedding layer(s). Your starting foods don’t need to be anything fancy. Simply adding a handful of fruit/veggie scraps (ideally chopped up) over top of your habitat materials can be a good way to get started, always making sure to cover food deposits with additional bedding.
NOTE: don’t worry if you have far more habitat material than you can add to your tray. This is actually a good thing, since this mix can be kept in a separate bin (with some ventilation holes) and left to age until you need to add more to your system. In some ways, it will be like creating your own living habitat material, which will be great for topping up your first tray and for starting up new ones.
As a related sidenote, if you are wondering how you should start up a new tray (later on), it is basically just the exact same process as with the first tray, minus the paper liner on the bottom. To help the worms move up, you can top up the lower tray with damp habitat materials (which can just be transferred over to your active tray when you decide to harvest the lower tray) before adding the new tray on top.
How Many Worms Should You Start With?
Another misconception people have about stacking systems is the quantity of composting worms they need to get the ball rolling. It’s important to remember that you are more than likely starting with a container (your first tray) that has a really small volume - often 15 litres or less. In our humble opinion, most stacking systems shouldn’t be started with more than ¼ lb or (at the very most) ½ lb of worms.
For your cover bedding layer, we recommend using bulky, absorbent materials like shredded cardboard. For extra protection you might consider using some form of “worm blanket”. This is a solid piece of material made from natural plant fibres such as jute, coir or hemp, usually cut to fit nicely over the surface of the system it is being used in.
Worm blankets are helpful for moisture management, maintaining a good C:N ratio, and for discouraging pests.
NOTE: our hemp blankets break down more quickly than some of the more typical, heavier worm blankets on the market. This has the advantage of providing you with more of an immediate habitat-enhancement effect, but means they will likely need to be replaced more often.
Harvesting a Stacking Tray System
The original stacking tray worm bin concept was developed mainly as a way to help worm composters separate the worms from their castings. As touched on, it is an upward-migration design; as new trays get added (gradually, over time), the idea is that the worms should continue to move up in search of the richest food sources and away from their own wastes. Best case scenario, you should be left with a lowermost tray solely containing rich castings, ready for use in your gardens or potted plants.
Unfortunately, theory and reality don’t necessarily line up with stacking systems - and it is very common to end up with quite a few worms remaining down in the lowermost tray. As such, we almost always recommend some form of additional light/migration harvesting to help separate the remaining worms from the finished vermicast.
Lucky for us, stacking trays themselves offer us a very easy, effective way to perform this separation!
This brings us back to the one potential exception for the upward-migration rule! In this case we will actually be encouraging the worms to move downward and out of the tray being harvested, into another tray containing habitat and food materials.
Step #1 - you can either prepare an entirely new tray with these habitat and food materials or (much more easily) simply use your uppermost active tray as your receiving tray. Whatever option you choose, just make sure there is enough material in the receiving tray so that it comes into contact with the bottom of the tray you’re harvesting. If there is any intact bedding etc material still left in the tray you are harvesting this can also be transferred over to the receiving tray.
IMPORTANT: remember what we said about lining the bottom of trays earlier. Unless your receiving tray is going to be a new lowermost tray, you shouldn’t line it. If you do decide to make it your lowermost tray, be sure to transfer everything over from your active tray(s), since it won’t make sense to have a lowest tray that is further behind than upper trays - this would just encourage the worms to move down and stay lower in the system.
Step #2 - place the tray with all the compost in it over top of the tray with all the habitat and food in it. (the receiving tray can simply be sitting on top of the reservoir platform like a typical lowermost tray), and then shine a bright light down into it. NOTE: you might consider blowing a fan towards the open tray as well, since air movement can also help encourage the worms to move down.
Step #3 - use a small garden hand rake (or worm rake) to loosen up the upper layer of material in the tray you are harvesting. Leave everything to sit for 10-15 minutes, then come back and gently remove this uppermost layer (a gloved hand can work well for this).
Step #4 - Loosen the next “uppermost layer” and continue the process until you are left with a completely empty tray. The compost you remove can simply be placed in a separate tub or tray as you go. Virtually all of the worms should end up down in the receiving tray.
If it seems like worms aren’t moving down quickly enough (i.e. you end up with some in the layers of compost you are removing), try roughing the material up a bit more and also leave the tray to sit for longer before scraping off the upper layer.
PRO TIP: empty stacking bin trays can be great for helping you harvest material from other worm composting systems as well! Simply dump in wormy material from the system you are wanting to harvest, and use the exact same approach described above. Instead of using another tray as your worm-receiving vessel, however, you would use a regular tub (set up with habitat/food) or whatever system you are transferring the worms over to.
Stacking worm bins are popular for multiple (perfectly good) reasons, but there are definitely some nuances involved in working with them effectively! The advice shared in this article should help people avoid some of the common pitfalls, and clear up some of the confusion associated with these systems. As always, don’t ever hesitate to reach out with any questions you have about stacking bins, or anything else related to composting!
Other Articles You May Be Interested In
Setting Up and Managing Your Urbalive for Worm Composting Success!
How to Feed Your Worms to Get The Best Results From Your Worm Bin
Smelly Worm Bins - Possible Causes & Effective Solutions
What Is “Living Material”?
Bedding - The Most Important Material in Your Worm Bin?
DIY Plastic Worm Composting Bins
How to Separate Worms from Their Castings
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