All About Worm Castings


The following are excerpts from (Duncan Carver) unless otherwise stated.  Some articles are not for the beginner.  More advanced information about the castings are at the end.

What Are So Amazing About Worm Castings

Castings are a totally organic, all natural soil enhancer.  Odorless and non-toxic, worm castings will not burn, even the most delicate plants.  Castings offer a concentrated source of calcium, magnesium, nitrogen, phosphates and potash in a form readily available to your plants.  The castings are created as various organic materials pass into, and then out of, the red wiggler worm, also known as Eisenia fetida.

Worm castings are the only animal waste that does NOT have a manure odor.  Worm castings have the fragrance of rich, healthy soil.  (The worms eat the bacteria off of the food scraps.)  Mix 10-20% worm castings.

Worm castings, a fine particulate matter produced by the worms, increase diversity in the soil.  The castings contain a highly active biological mixture of bacteria, enzymes, remnants of plant matter and animal manure.  They are rich in water-soluble plant nutrients and contain 50% more humus than what is normally found in topsoil.  They also contain a high concentration of nitrates, phosphorous, magnesium, potassium, and minerals such as manganese, copper, zinc, cobalt, borax, iron, carbon, and nitrogen—all in natural proportions.

The beneficial nutrients found in castings are absorbed easily and immediately by plants (unlike chemical fertilizers and manure); they will never burn plants.  Worm castings can be sifted for starting seeds.  Mix with coir or peat moss and vermiculite or perlite.  Do not use more than 20-40% castings in the mix.  The castings are perfect for use on vegetables or flowers.  Incorporate I part of castings to 10 parts of soil.

The overriding emphasis today is on vermicompost (worm castings); the ultimate product is aerated compost tea.  Dr. Norman Arancon from the University of Hawaii-Hilo is doing research on the benefits of vermicompost on plant growth.  He listed the known benefits of vermicompost.

·         “Increases microbial populations

·         Increases microbial diversity

·         Aids in decomposition of organic matters

·         Slow nutrient release

·         Aids in pest suppression·         Aids in pathogen suppression

       Vermicompost won’t kill or eradicate pathogens.  They are still present, but will remain non-virulent if kept in check by other micro-organisms. If the pathogen does attack, the plants will be able to better fight it off.

·         Aids in disease suppression

·         Regulates plant growth regulation.  If VC tests positive for hormones, fruits are bigger and will flower several weeks earlier.”

Dr. Norman Arancon, University of Hawaii-Hilo


Benefit Of Using Worm Castings In Your Plants and Garden

100% natural

Safe and odorless, won’t burn roops of delicate seedlings

Enriches and improves soil

Regulates the availability of essential plant nutrients

Enhances germination and early growth of seedling and cuttings (auxins)

Stimulates flowering and improves fruit seed set and quality

Stimulates the natural activity of beneficial soil microorganisms

Promotes the activity of enzymes and natural plant growth regulators

Invigorates and rejuvenates potted plants and perennials

Increases the ability of the soil to retain moisture

Evidence of the elimination of white flies from flowers

Evidence of the elimination of aphids from roses

The Scent of Roses Farm, Rockville, RI

A quick and simple way to check the quality of so-called pure worm castings.

Pure worm castings will look like black coffee grounds!

Take 2 wide mouth 20 oz drink bottles and place 4 oz of pure worm castings in one bottle and the same amount of another producer of worm castings or pure worm castings.

Fill both bottles ¾ full with tap water and shake well and let stand for 5 minutes.


Check for weed seeds and other materials (compost) not consumed by the worms.  This is typical of vermicompost.

Sand will settle out first.  It is common for manure based fertilizers to contain a lot of fine sand or sand added for weight.

Pour off the liquid and dump the sediment out and examine.  If it feels and looks like mud, then that is probably what it is.  If it retains much of the

Original characteristics then it is pure worm castings.  Each pure worm cast is coated with calcium and takes time to dissolve.

Worm castings should crumble when they are ready.

Ways Of Incorporating Worm Castings Into Your Garden

Add one tablespoon of worm castings to the soil at the bottom of each transplant hole.

Before planting row crops place castings right into the top few inches of soil.

Use the castings as a top dressing, or mix at a rate of 20% to make a potting mix

Castings may be used as a soil enhancer for lawns, spread at a rate of 1-5 cubic yards per acre

There Is a Huge Difference Between Vermicompost And Pure Worm Castings

The term “vermicompost” is used much like “compost.”  Vermicompost contains worm castings and other organic matter that has been partially or fully composted.  The amount of pure worm castings will vary from batch to batch and from one vermicomposting facility to another.

Speaking of testing, it is really important to emphasize once again that while the results of scientific research are incredibly valuable they certainly aren't set in stone.

Use them as a guide, but don't be afraid to experiment with your own vermicomposting systems as well!

Speeding Up The Vermicomposting Process

There are a number of ways you can help to speed up the vermicomposting process, thus producing more worm castings, faster.

The design of your worm beds can also have a fairly major impaction the time required to produce finished vermicompost. If you are simply piling materials up on the ground, you may want to try switching to a raised bed system. Lots of aeration (providing

oxygen) is very important for an optimized composting process.  Piling materials in a windrow, while very easy, won't allow for the same amount of oxygenation of the materials so it can potentially slow down the process - particularly in the lower

reaches of the bed.  The ultimate optimized vermicomposting system is some sort of

flow-through digester, whereby waste materials are added from the top and (eventually) finished vermicompost is harvested from the bottom (the floor typically consists of some sort of grate that

The type of food materials you use will also have a major impact on the processing speed in your beds. You will likely want to avoid (as much as possible) any wastes that contain a lot of resistant (slow to decompose) wastes like woody or fibrous

debris.  Carbon-rich materials in general will often be somewhat slow to

breakdown so it is important to help the vermicomposting process as much as possible.

One great way to do this is by shredding/grinding and mixing wastes before adding them to your worm beds. This exposes far more surface area for microbial colonization, thus helping to initiate decomposition. It also helps to create a much more uniform starting material, which of course will tend to result in a more uniform end product as well.  Animal manures are an excellent food source for composting worms.

Some varieties such as rabbit droppings work well on their own and will be broken down very quickly into a nice uniform vermicompost.

Other manures will likely need to be mixed with c-rich materials like straw (unless it is used as bedding and ends up mixed with the manure already), then aged or 'hot composted' before adding to the worm beds. Again, if you are able to pulverize the mixture somehow before it is fed to the worms that will also help a lot.  Once you hit upon a nice uniform mixture of materials that the worms love and seem to process quickly, I'd definitely recommend trying to be consistent with it. This way the worm population will be used to it and will even potentially become better at processing it over time (since future generations of worms will be born in it and thus very well adapted to the habitat).

Worm Castings Should Never Dry Out Completely

One of the main beautys of wormcast is it's high population of a diverse range of microbes which it contains. These microbes need moisture to survive and will stay in the wormcast until it is used in soil.

Once in the soil, the microbes in the worm cast will stay to proliferate as organic matter. These microbes are important in maintaining the soil-ecosystem and to mediate the nutrients for the plants. The microbes include protozoa, beneficial nematodes, mychorrhizal fungi and bacteria.

Many other organisms have a diet of these micro-organisms.

A high population of microbes will encourage these organisms to populate the soil, increasing soil eco-diversity and the overall health of soil.

One great example are earthworms themselves which come to aerate and mediate the soil with their movement and wormcast!  Microbes also help in converting minerals into a soluble state for the plants. Many nutrients are locked up in larger sizes, or in a form which plants cannot absorb. These nutrients require these microbes to convert it into a ready absorbable form. So with a more diverse set of microbes, the more the nutrients are readily available.

Is It Beneficial To Spread Wormcast Over The Lawn?

In some lawns you may see brown patches, areas where grass cannot and does not grow in. This can be due to various reasons such as soil compaction leading to clay soil with no water drainage and fungal diseases.

Depending the cause of your problem, wormcast can sometimes fix brown patches. But the overall spreading of wormcast through the lawn will help in creating a fantastic and healthy looking lawn.  Castings may be used as a soil enhancer for lawns, spread at a rate of 1-5 cubic yards per acre.

How do you spread wormcast, and especially how do we prevent the lawnmower in picking it up?

The first thing to do is to spread the wormcast after mowing the lawn. When the grass is short, the wormcast will be able to reach directly onto the soil much more easily. Once it is in contact with the soil, the nutrients, humus and microbes from the wormcast will naturally immerse themselves into the soil.

Promoting Properties Of Castings

The growth promoting properties have been clearly shown to be independent of the plant-nutrient levels in castings. By providing test plants with all their nutritional requirements - in the form of standard inorganic fertilizers - researchers have demonstrated that the additional growth of the plants treated with castings was due to other factors.

Precisely WHAT these factors are has been the big question.

In a 1998 BioCycle report by Subler et al., the authors speculated that the increased growth was "perhaps related to enhanced micronutrient availability, the presence of plant growth regulators, or the activity of beneficial microorganisms in the castings".

The presence of elevated levels of various plant growth regulators - such as auxins, giberellins and cytokinins - in earthworm-worked material has in fact been observed and reported by researchers well before 1998 (eg. Tomati et al., 1983), thus making this a promising possibility.

Some significant progress in this field was reported by Atiyeh et al. in 2002.

For the first time, a group of researchers (not surprisingly, a team from Ohio State University) was able to pinpoint an exact mechanism responsible for at least some of the additional growth promotion in plants (while others HAVE found plant growth regulators in castings, they've never provided conclusive evidence that these substances were indeed directly responsible for the additional growth).

The study involved plant growth trials testing the addition of varying levels of humic acids - extracted from worm castings (made from pig manure and food waste) - to determine if they had any effect on plant growth. The set-up of the experiment was very similar to previous work by OSU researchers testing the growth promoting ability of the castings themselves. As such, all plants were provided with full compliment of required nutrients, so as to ensure that any and all additional growth observed was independent of improvements in plant nutrition.

The team found that not only did the humic acids stimulate significant plant growth, but the effectiveness at varying concentrations followed a similar pattern to that reported in the castings studies.

That is to say that a significant growth response was observed at relatively low concentrations of humic acids, and this growth response increased as the  concentration of the humates increased --up to a certain point (which varied, depending on the starting material, plant species being tested, and the potting mix being used).

Treatments with higher concentrations of these humic acids often brought about a decline in plant growth. The authors concluded that the growth response was specifically due to either the hormone-like properties of the humic substances themselves and/or actual plant growth hormones adsorbed onto the surface of the humates.

For those of you unfamiliar with 'humic' substances, these are large, highly complex, and highly stabilized compounds which offer a wide variety of beneficial properties when present in soils. I'm sure most people have heard of 'humus' - which is basically the dark, rich earthy material you find in a good compost or at the bottom of a well rotted pile of leaves.

In a more recent OSU study (Arancon et al. 2006), humic acids extracted from worm castings were once again found to positively (and significantly) impact the growth of various plants species.  Beyond the positive impact of the humates, and the likelihood that plant growth regulators are somehow involved (both discussed in the 2002 article) there doesn't appear to have been any further developments in this area.

Given the fact that we at least know (with a pretty high degree of certainty) that humic substances play an important role in the beneficial properties of worm castings, one might wonder why similar properties haven't be reported for 'regular' composts, which certainly contain plenty of humic compounds as well.

It likely once again comes down to the considerable differences in the way castings and normal composts are produced.

According to Dominguez et al. (1997), vermicomposting not only accelerates the humification process, but it results in a more thoroughly humified end product. This is likely attributable to the fragmentation and extremely high microbial activity occurring within the earthworm digestive tract.

I must say that spending all this time immersed in the academic worm castings literature as of late, has certainly served to renew my fascination with this topic. I'm sure you will agree that there is considerable (solid) evidence to indicate that worm castings do indeed live up the the 'hype' in a lot of ways.

It is a truly incredible material for a variety of different reasons.

Considering how small the body of vermicomposting literature in general is in comparison to mainstream compost science, however, I am also reminded of the fact that there is a serious need for further research in this field. Hopefully with growing public awareness of, and interest in vermicomposting (what can I say - I'm an optimist at heart), we'll see this come to pass.

Worm Castings... Disease Suppression

Over the years there has been considerable research examining the disease-suppression potential of thermophilic (hot) composts, but relatively little, in comparison, conducted using vermicomposts (again, recall that we are basically using this term as a synonym for 'castings').

Nevertheless, there is still a respectable (and growing) body of evidence to indicate that castings do indeed possess properties that can help to protect plants against a variety of diseases.

This past fall I was fortunate enough to have the opportunity to interview (for an article on my website) Allison Jack, a PhD candidate at Cornell University who has been looking into the area of compost-mediated plant disease suppression for her thesis project.

One component of her research has centered around the suppression of the 'damping off' pathogen, Pythium aphanidermatum, brought about via the addition of dairy manure worm castings (Tom Herlihy's "Worm Power" brand). Specifically, she has been trying to determine what mechanisms are responsible for the significant reduction in disease incidence when castings are added to the soil blend.

One thing that has been determined without much doubt is the fact that the microorganisms in the castings are primarily responsible for the disease suppression - at least in this particular case.

When castings were heat sterilized before being added, most of the seedlings were killed by the pathogen - similar to treatments without any castings added.

What makes this even more interesting is the evidence suggesting that this microbial protection is not the result of the 'good guy' microbes attacking or even out competing the pathogen - rather, it seems to be due to some sort of alteration of chemical cues.

Pythium colonizes seeds/seedlings via swimming 'zoospores', which rely on chemical cues in order to find their host, so when these cues are no longer present the guidance system is basically thrown off and many of the zoospores never reach the seeds.

One of the real challenges in this field (and compost science in

general) is that not all castings are created equal. Aside from the basic 'good'/'bad' quality considerations, there are so many different variables to consider - often making it difficult to draw reliable parallels between different studies (since different castings are typically used).

Something Allison pointed out is that the starting material (the 'waste' used to make the castings) itself can be a very important consideration - in other words, just because her 'dairy manure castings' effectively suppressed Pythium in cucumber seedlings, that doesn't necessarily mean that food waste castings would have produced the same results, or that the manure castings would be as effective against other diseases etc.

A study conducted by Szezch and Smolinska (2001) demonstrated that different starting materials can result in significantly different worm castings (in terms of disease suppression). The researchers tested four different types of castings - three using cattle, horse, and sheep manures, and one using sewage sludge - in order to assess their ability to suppress Phytophthora in tomato seedlings.

While all of the manure castings did indeed provide significant protection against the disease, the sludge castings offered no protection at all. What's interesting is that, similar to Allison's findings, the manure castings did not actually reduce the abundance of the pathogen, which seems to once again indicate that there can be mechanisms at work other than direct attack/competition.

One thing that is very important to note about this particular study however is the fact that the sludge contained three times more zinc than is legally permissible in soil, and the material was shown to hamper the growth of the plants in general (and even brought about a reduction in pathogen abundance - although this didn't help reduce incidence of disease). This is a prime example of why it is always important to look a little deeper, and not to draw any major conclusions (i.e. 'sludge castings are bad') from the results.

In an earlier study by Szczech (1999), cattle manure castings were found to significantly inhibit the infection of tomato plants by Fusarium. In this case however, direct antagonism against the pathogen seemed to play an important role.

Microscopic examination of the pathogen organisms in treatments where castings were applied revealed that the Fusarium had been attacked and colonized by other microbes.

Direct antagonism also seemed to play a major role in the disease suppression reported by Utkhede and Koch (2004). The researchers found in this case that applications of worm castings tea resulted in as much as 63% reduction in bacterial canker incidence in tomato plants.

We'll certainly be talking a lot more about castings tea in future newsletters, but I thought this was an interesting finding to mention, and it's certainly applicable to the present discussion.

While all of the above-mentioned studies (and others) do seem to indicate that castings can potentially offer effective stand-alone protection against plant diseases, I came across a couple of other interesting research papers that demonstrated that the use of castings in combination with other disease suppression agents can be even MORE effective.

Sahni et al. (2008a), showed that castings used in combination with biocontrol bacterium, Pseudomonas syringae, resulted in the highest level of protection against 'collar rot' in chick peas.

Interestingly enough, Sahni et al. (2008b), showed that the use of certain chemical agents along with the castings and the same biocontrol organism provide more protection still.

I wanted to mention these last two studies, since they highlight the importance of not necessarily thinking of castings as the 'be all, end all' solution - but rather as one

(potentially) effective component of a multi-pronged, integrated approach. The same can be said of their growth promoting abilities - as the OSU research

seems to indicate, the best results are achieved when castings were combined with conventional fertilizers and methodology.