Composting Climates


The various species of earthworms have different environmental requirements which are necessary for their propagation and continued health. These requirements will inevitably dictate whether one particular “family” of worms will be suitable for culture in any given circumstance. For instance, though many people may be interested in the possibility of raising Lumbricus Terrestris (The Nightcrawler, or Dew Worm) in the house as a source of fishing bait, this is simply not very plausible when we consider that this particular worm prefers temperatures in the area of 5-10 degrees Celsius. During the heat of the day, this large member of the earthworm family retreats to the depths of his burrow, venturing out only in the late evening, or early morning, the coolest available times. (Burrows have been found to extend to a depth of over 30 feet.) Thus, if we wish to culture this animal in the confines of our homes, we will require the ability to refrigerate at least a part of the available space. Even then, however, the number of additional considerations will eventually convince most people that nightcrawlers should be “harvested”, or “farmed” outdoors, rather than “cultured” in an indoor setting.

On the other hand, the two most commonly-used worms for vermicomposting, Eisenia Foetida and Lumbricus Rubellus, are the most popular precisely because of the ease in replicating within our homes the environmental conditions they generally prefer. Perfectly suited to an indoor existence, the culturing of these animals presents next to no problem, requiring only a minimum of effort, and presenting no hardship for those of us who share their place of residence. The fact is, in the absence of the normal hazards these worms usually face in their outdoor habitats, they are found to grow faster, stay healthier, live longer, and reproduce at an increased rate indoors than they would in their natural outdoor environment. Thus, indoor culture turns out to be heaven for them, and a great benefit to the “landlord” who will have a great new way to convert his organic waste materials into a wonderful “food” for his plants, lawn, and garden. To achieve this heaven, there are certain environmental requirements that must be met and maintained. These “requirements” can be broken into three main areas, and we will look at each of these in the following paragraphs. (It is assumed that the worms in question have already been housed in an adequate bedding material, and are being supplied with a sufficient quantity of food.)


If we consider that the earthworm (contrary to what its name implies) is actually a creature of the water, it is not hard to accept that moisture constitutes the most urgent of its requirements for life. In my own experience, however, the problems most often incurred in a worm bed involve too much moisture, rather than not enough. As in most things in life, a suitable balance must be found and maintained for optimum performance, keeping in mind that this balance may have to be altered to accommodate specific needs. Let us first take a look at the lower end of the moisture scale.

Research has shown that in the natural scheme of things, the greatest abundance of earthworms will be located in soils which average between 12% and 30% moisture content (Minnich, 1977). If this amount of available moisture should fall too low, the earthworm will begin to lose its internal water content, and a series of biological events will begin to occur which, if unchecked, will eventually result in the death of the animal. (In 1956, a researcher named Roots determined that a worm could lose as much as 75% of its moisture without dying.) During the final stages of dehydration, a worm will even expel coelomic fluid from within itself in a desperate attempt to moisten its own body. At this point, total submersion in water may be the only way to prevent the worm’s demise.

Earlier this year (1995), I ran some tests in which I placed a population of worms in a bin which I consistently kept much dryer on one side than the other. Once the worms had become established in their environment, I performed two tests. First, I stopped adding food to the side of the bin which contained the adequate moisture supply, installing an amount of wet food at the far end of the dry region. The worms wasted no time in travelling through the dryer material to reach (and take up residence) directly inside the food supply, as well as in the damper bedding immediately surrounding it. Next, I set up the bin in basically the same manner as before, but this time I placed in the dry region, a supply of food which contained no moisture of its own. It took a little longer, but this food also was consumed by the worms, though I never found them to actually take up residence in this portion of the bed. What I concluded from this is that the worms can store enough moisture in their bodies (obtained from the damper region) to not only travel through a very hostile environment to reach a food supply, but also enough to dampen the food once they acquire it, and still make it back to the friendlier region before sustaining critical damage. (The significance of these results will become apparent a little further on.)

In traditional vermiculture, it is generally accepted that the optimum moisture level for a worm-bin is somewhere between 50% and 80%. Even this, however, is not as wet as it may at first appear. Consider just how much peat moss, for example, is required to make up 10 pounds. Then consider that to achieve a moisture content of 80%, it is only necessary to add roughly 8 pints of water. (A pint’s a pound, the world around.) If you take a handful of worm bedding, and squeezing it as hard as you can you produce a stream of water, the bedding is too wet, if no water is released, then the bedding is too dry. A few (I stress few) drops of water oozing from between your fingers indicates adequate moisture. There are times, such as when bait-sized worms are required, or immediately following an artificial drought (the reason for this procedure will be explained in another article), that larger amounts of water may be called for, but 80% is adequate most of the time. As we will see, this is crucial to the health of your worms.

A situation of too much moisture is very often arrived at when a newer “breeder”, or “vermiculturist”, attempts to keep the worm bedding consistently, and evenly moistened. Observing that the top layer of the material is dryer than it “should” be, more water is added to the bed. What results, however, is a layer of “properly-moistened” material laying on top of lower levels which progressively become more and more swamp-like. The lower regions of the bed will always be wetter than the surface layers. Now if we go back to the results of those tests I mentioned earlier, we can see that as long as there is moisture available to the worms anywhere in the general vicinity, they will normally make out just fine. There is really no need to saturate the entire amount of bedding, though some moisture throughout is recommended to prevent damage to the worms delicate skin as it moves about in search of food (or a good-looking date to share the food with.) In addition to reducing the amount of time spent watering the beds, less watering will help to prevent a number of other problems.

First of all, one of the only reasons for a worm bed to develop a bad odor is the presence of anaerobic bacteria. (These are the same culprits responsible for the foul smell emanating  from a garbage bag, or can, that is commonly left sealed.) These particular bacteria work in the same manner as aerobic bacteria, but in the absence of one vital ingredient…air. Thus, if too much water is added to the worm-bin, the air can be forced out of the lower areas, creating perfect anaerobic conditions, and resulting in an odor of indescribable proportion. By the way, the worms themselves will not tolerate these conditions, so if you see the entire population of your vermicomposter apparently heading south for the winter, you might think about easing up on the water supply. There is also another problem, though you may not notice this one until it kills your worm population.

When you first placed the worms in their new home, the bedding was made up of fresh material (hopefully), which in due course would become simply another ingredient in the final product. Then food was added, and the worms went about their usual business of eating everything in sight, altering the material as it passed through their remarkable little bodies, and finally excreting it back into the bed from which it will eventually be harvested, and used to “feed” some very fortunate plant. Like every other animal in the world, however, a worm is unable to remain healthy if forced to live in his own waste material. Thus, we change the bedding on a regular basis, preventing the castings from reaching a level where they would be toxic to the bin’s inhabitants. By overwatering,  however, we speed up the process, spreading the castings with the run-off. (The substance which will eventually kill the worms is also the same substance that we wish to save for the plants, and a lot of this can be lost in the excess water.)

At any rate, it soon becomes evident that while moisture is crucial to the survival of our friendly little worms, moderation is the key! Keep the bedding moist, but never soggy, using as little moisture as possible to get the job done. Always check the lower regions of the bed (a moisture-detector commonly used for potted plants works very well) as well as the surface, and don’t worry if there are some portions of the bed drier than others. As long as there is always some available moisture, the worms will be happy and when you see how much less time you spend worrying about precise moisture measures, so will you.



When we talk about temperature in regards to worms, the most important thing to remember is that while the worms will survive a fair amount of variation in their climate, they will only do so if these variations occur slowly, over a period of time. Taking a worm-bin from a house which is a comfortable 20 degrees Celsius, and moving it out into a winter temperature of -10, even if only briefly while on the way to the car, is a sure way to solve the problem of overpopulation in the bin. The same problem can occur in reverse. If you have the worms out on the balcony for instance, and fearing an early frost you move them from a temperature of 5 degrees Celsius into the heated living room, try not to be surprised if you later notice that a lot of the survivors are in mourning for missing loved ones.

Generally, the most suitable temperature range for Eisenia Foetida and Lumbricus Rubellus has been shown to fall between 13 and 22 degrees Celsius, a range which is also quite convenient for those of us who live with them. Temperatures which fall outside this range can affect the worms in several different ways, not all of which are as final as death.

As the temperature drops below 10 degrees Celsius, the amount of food eaten by the worms will also decrease. The worms will be less active, and possibly move a little lower into the bedding (unless it is a cold floor causing the problem, in which case they will move nearer the surface.) At 4 or 5 degrees Celsius, the adult worms may stop producing cocoons, and the growth rate of the younger worms will diminish. This is where it gets a little tricky. Of all the material I have studied on the culturing of red worms, only once have I come across a writer who is apparently of the same mind as myself where this next matter is concerned.

Time and time again, I have read statements to the effect that a worm cannot survive a solid freeze. Now if what this statement means is that a worm cannot survive being frozen solid, then I agree 100%. However, if this statement is meant to imply that any worms left in the soil (yes, I said soil, but that’s another article) after the onset of winter are destined for that great compost-heap in the sky, then I disagree just as strongly. Two years in a row, I went out to my yard in the spring, while the ground was still frozen, and using very strong tools managed to dig a chunk of frozen earth out of the garden area. Upon looking at the profile of the soil, the presence of red worms curled up in little air pockets in the soil, is not a sight you can easily overlook. Knocking a couple of these guys out of these little pockets, I was very impressed on each of the two occasions when only a few moments passed before the worms in question slowly woke up, stretched out, and proceeded to look rather foolish as they tried to work their way back into the still-frozen ground. Since we are talking about holes which were only a few inches under the surface (and I was living in Prince Albert, SK, in Canada), no one will ever convince me those worms did not survive a solid freeze. Obviously, given adequate time to adapt and prepare, they somehow managed to avoid being frozen solidNOTE: Further research over the years since I first wrote this article has taught me that there has been some suggestion that red composting worms at least, and probably most other worms also, contain within their bodies a form of antifreeze that actually stops their bodies from freezing solid while they hibernate in those little air-pockets that I mentioned earlier, thus allowing them to survive the winter in the ground despite our harsh northern climates. 

Pushing things up to the other side of the scale now, we find a similar situation when we talk of excessive heat. Though the most suitable temperatures for consumption of food, and reproductive processes in regards to the worms we have been discussing are generally agreed to be in the moderate range mentioned earlier, when properly acclimated, red worms will continue to breed, feed, and grow very well in temperatures up to 30 degrees Celsius, if adequate moisture is always present. In fact, research has shown that worms raised from hatchlings to adulthood in temperatures considerably higher than the norm, may even develop, and reproduce, at rates faster than members of the same species raised at lower temperatures, or outdoors (Minnich, 1977; Hartenstein, Neuhauser, and Kaplan, 1980.) The same does not hold true, however, for worms originally raised at lower temperatures, with death often resulting (Hartenstein, 1978; Mitchell, 1978.) So once again, we see that it is often a case of what the particular batch of worms is accustomed to, and it also bears mentioning once again, any change in temperature should be a gradual one.

There is a final point which should be mentioned in regards to temperature. Always bear in mind that if the worm-bin has sufficient moisture content, the temperature in the bedding will average anywhere from 5 to 10 degrees lower than the surrounding air. There are times when this will be an important consideration. And finally, a word of caution. Several of the books which are available on vermiculture recommend using cold water as a way of bringing down the temperature in a bed which is suspected of being too warm. Possibly there may be no harm in this idea, but I for one have had the experience of standing in the shower when the hot water suddenly ran out, and…well, you get the idea.


Though there is not an awful lot to say on this last topic, what there is to say really needs to be said. We have already mentioned earlier that worms are not fond of anaerobic bacteria, and if subjected to conditions of that nature, they will either leave the offending area (I really wasn’t kidding), or if they are unable to take this course of action, they will die. In addition to this, however, there is yet another problem. Though it may not kill your worm population with any great speed, if it is allowed to occur at all, it can result in a worm bin becoming a mass burial site before the problem is even noticed.

As the worms go about the business of everyday life, simple as it is, they will need to breath, just like most other living creatures. (Actually, the process of osmosis makes a worm rather different than those of us with lungs, but the end result is pretty much the same.) Gradually, the available oxygen is used up and replaced with carbon dioxide and other miscellaneous waste gases. Unlike those of us who live above-ground, however, the poor little worm is stuck beneath the soil, or bedding, in close proximity to the “toxic” fumes. In addition to this, the decreasing amount of fresh oxygen can result in an increase in heat, and the increase in heat will result in a similar rise in the oxygen requirements of the worm. Fortunately, the whole situation is easily rectified, and only requires very infrequent attention.

About once every two or three weeks, the top few inches of the bedding should be gently stirred, allowing for the escape of any built-up gases. (This will also go a long way toward preventing the bedding from becoming too densely packed.) The lower levels of the bedding can also be stirred, but on a far less frequent basis. If you are in the habit of burying the food you are placing in the worm-bin, it is quite possible that the bedding is already being stirred sufficiently, and all you really need to watch out for in that case is the accidental saturation of the bin. If you are just in the process of setting up a new system, you should keep in mind that a larger surface area is beneficial in this regard.

To sum up, if the basic sense of these various levels is maintained, and if sudden, or drastic changes can be avoided, the end result should be healthy, happy, and productive worms, and less work and worry for yourself. (PLEASE NOTE: None of the above procedures should in any way be interpreted as implying a substitute for regular cleaning of the bin, or refreshing of the bedding material.)

Original Text

Copyright © 1995, D. Brian Paley

And there we have it, Vermicomposting article number 4. I really hope that some of you gardeners out there are getting some use out of these articles, and I hope I’m not just boring a bunch of people with them. At any rate, I really do believe in this process, and if you ever had the opportunity to study the current state of things regarding our society’s problems with Organic Waste Disposal, you might just understand why. I mean when I see a city like Vancouver shipping our garbage to Oregon to have it buried in the desert or whatever it is they’re doing with it, the whole idea of just feeding it to earthworms and making good healthy soil out of it  suddenly makes a lot more sense. At least to me. But that’s another story, for another time. So until then…

Composting Climates

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