Living Material (LM) refers to stable organic matter that is rich in beneficial decomposer microorganisms. It can be used as a highly-effective, all-natural compost activator/accelerator, and a worm-habitat enhancer in vermicomposting systems. They can be further divided into "primary living materials" and "secondary living materials", based on their structure and level of decomposition - both of which can influence their potential end uses.
Primary living materials offer the rich microbial community along with a beneficial (bulky, absorbent) structure - making them an excellent choice for enhancing the habitat of worm composting systems, and improving your layered composting set-ups. In addition to the usual highly decomposed/stabilized (and microbe-loaded) material, these LMs will typically also have a lot of carbon-rich wastes that have not fully decomposed.
Secondary living materials, on the other hand, consist almost entirely of organic matter that is very well-decomposed/humified. They are excellent for microbial inoculation of composting systems, but they don't offer the same structural habitat benefits of primary LMs, so they should be used more sparingly.
Examples of Primary Living Materials
- Aged, bedded horse manure (and other similar bedded livestock manures that have been allowed to go through a partial decomposition/composting process)
- Rotten straw and hay
- Rotten wood chips
- Rotten cardboard
- Partially-decomposed fall leaves
Examples of Secondary Living Materials
- Quality finished castings and other composts
- Bulky compost/castings screenings (note: in some cases, if there are enough structural elements being screened out as well, you may end up with a mix that could be a good primary LM)
- Really rich organic soil
- Fully decomposed leaf mold
Key Features of a Quality Living Material
- It should have a pleasant, earthy smell (there should be NO foul odours)
- It will (usually) be darker in appearance than the materials it was derived from
- It will often have a diverse ecosystem of invertebrates associated with it, but shouldn't be attractive to most fly species (eg. if you see lots of flies or maggots in/around the material, it most likely indicates it hasn’t broken down and stabilized enough)
What Shouldn’t be Considered a Living Material?
It's important to remember that the term "living" refers primarily to the rich microbial community living in these materials. LMs should never contain any living plants or plant matter (eg fresh grass clippings, weeds etc), or other rich wastes that have not fully decomposed.
Bagged, store-bought composts/manures/soils can add value to your gardens, but these are not really living materials, especially not ideal for use in smaller systems. They tend to be quite sterile, and can often contain salts that could be particularly harmful in vermicomposting systems.
Regular garden soils are also not ideal living materials in most cases. Soils with some clay content, for example, tend to be very heavy, and turn into mud when moistened. This can impede air flow and/or cause other issues in a composting system.
Examples of Living Materials That Can Be Easily Produced or Obtained
1) Aged, Bedded Livestock Manures
Even if you don't have your own livestock, there are farms and stables in most regions where you should be able to obtain (often for free) a supply of well-aged, bedded manure. The best choices include horse, rabbit, goat, sheep, and other similar herbivore manures that have been mixed with a lot of carbon-rich bedding, such as straw, and then heaped up and left to sit for at least a month or two outdoors (exposed to the elements). Aged, bedded poultry manures can be used in a similar way, but they will most likely need to sit for a lot longer before they can be considered a quality LM. Remember, good living materials will be quite dark in colour (compared to starting materials), and have a nice rich, earthy smell. In the case of aged manures, there should never be a manure or ammonia odor, or any other unpleasant (eg anaerobic) odors. NOTE: fresher manures can be valuable for composting/vermicomposting as well, but need to be used more carefully. On the flip-side, also note that manures that have sat outdoors for many months, or even years - and have turned into rich soil - should be used as secondary LMs (i.e. they will be better suited for inoculation than for providing beneficial system structure)
2) Composts and Screenings from Composting/Vermicomposting Systems
Anyone who is active (and at least relatively successful) with layered composting or vermicomposting systems will naturally end up with some form of compost, as well as bulky (usually high-carbon) debris that hasn't completely broken down yet. Both of these can be beneficial for microbial inoculation - and in some cases structure enhancement - when added to newer systems.
3) Decomposed (Carbon-Rich) Organic Matter
Most property owners will end up with at least some carbon-rich organic matter that's been left to sit outdoors for a long time. Examples can include accumulations of fall leaves, wood chips, straw/hay, or mulch. Over time, these types of materials will tend to develop a rich fungal community and become home to a wide range of invertebrates, making them even more beneficial as composting (especially worm composting) system amendments.
Great Ways to Put Living Materials to Use
Primary Living Materials
Vermicomposters who have good access to primary living materials, such as aged-bedded horse manure, can greatly enhance the overall quality of their worm bin/bed environment by using it as one of their main habitat materials. Layer or mix it in with regular bedding materials, along with smaller quantities of food (we generally recommend a 70/30 balance of habitat/food materials). These types of LMs can also be excellent cover layers for your food deposits (with or without additional bedding) if you happen to have a good supply of them.
In layered composting systems these bulkier LMs can be a fantastic way to increase air flow and water-holding capacity - and for helping to ensure that you have rich microbial populations - throughout the system. Sandwiching thin layers of rich "greens" in between thicker layers of "browns" and living materials all the way up (also making sure all your layers are nicely moistened as you go) can be a very effective, yet relatively simple, start-up strategy for most layered systems. It may also decrease the need for any sort of turning/mixing later on (especially if you add composting worms as well).
Thick layers of primary LMs can also be highly effective for masking the odors associated with decomposing wastes, helping to reduce the likelihood of pest invasions (or unhappy housemates, in the case of indoor systems). Harmful gasses like ammonia can also get trapped in these layers, where they are converted into other valuable compounds, helping to conserve nutrients and create a safer environment for composting organisms.
NOTE: In larger systems, it is important to remember that the major boost in microbial activity from LMs can also lead to a lot of heating (especially with richer LMs like aged manure). In a regular composting system this can be beneficial of course, but in vermicomposting systems you can run the risk of harming or even killing your worms. We recommend either allowing your larger systems to age/compost until temperatures are back down below 30 C, or adding your worms down in the very bottom of the system (special below-ground zones can be even better) to help ensure they can avoid the high temperatures further up in the system.
Secondary Living Materials
Sprinkling in finished composts or castings as you set up your vermicomposting or layered composting systems can be an excellent way to inoculate your starting materials with countless beneficial microbes.
Mixing your food scraps with modest amounts of these LMs before adding them to your worm bin (or just sprinkling them in over top after they've been added) can also be a great way to speed up the breakdown process and even reduce odours in the bin.
Final Thoughts
The use of living materials in composting systems - especially vermicomposting systems - can be a simple-yet-effective way to boost the population of beneficial microorganisms and - in the case of primary LMs - greatly improve the overall structure of the system. Even if you are just starting out, there are a variety of ways to obtain an initial supply - maybe right in your own backyard!
We strongly encourage everyone to give living materials a try, and know you’ll be glad you did!