Appendix II: Quality standard for vermicast

A standard analysis of vermicast should reveal the following:



Quality standard



(carbon:nitrogen ratio)

Indicates stability.

A ratio of more than 20:1 indicates that the product is either not genuine vermicast or that the worms have been allowed insufficient time to convert it.

If a producer has added fine sawdust as a cheap filler (which you won’t necessarily see), the ratio might be as high as 500:1. Similarly, the addition of sand produces a very low ratio.

Extremes such as this disqualify the produce as vermicast.

15:1 minimum

18:1 maximum

If the ratio is more than 20:1, the vermicast will have a noticeable nitrogen demand and restrict plant growth. (The activity of the microbial population in vermicast is concerned mostly with reducing the carbon level by converting it to carbon dioxide.

All available nitrogen is taken up forming populations, leaving nothing or very little for the plant roots.)

Below 20:1, nitrogen becomes available to the plant roots, the plants are able to photosynthesise and growth is promoted. Given the choice, plants do not draw CO2 from the atmosphere; the underside of their leaves is roughened by the presence of stomata, through which CO2 is absorbed as it percolates up through the soil to the atmosphere.

However, if the ratio falls too far (below 15:1), the CO2

release and photosynthesis rates begin to decline andgrowth irestricted again.



Specific Gravity orweight per volume


means of checking whether the product hasbeen adulterated by the addition of sand or clay (heavy) and/or sawdust (light).



This translates as between 300 and 800 grams  per litre.

The moisture, mineral and vegetative matter content all contribute to this measurement. Vermicast should have a high vegetative (and organic matter) content. Water has an SG of 1, mineral matter (sand or clay) greater than 1 and dry vegetative (and organic) matter less than 1.  The combination of these should produce an SG of between 0.3 and 0.8 in vermicast. If the product offered as vermicast is less than 300 or greater than 800 g/l it's an indication that it may be fake.

 Particle size

Aggregates form the basis of stable soils.

4 mm maximum

Vermicast is formed in microns that are glued together into aggregates with polysaccharides. Most vermicast will pass through a 2 mm screen, but all should pass through 4 mm.



Quality standard


Moisture content

The valuable bacterial population of worm castings requires the right moisture level to survive.


While most members of the bacterial population  makespores before death, not all do, and allowing worm castings to dry may destroy some of the bacteria’s microbiological benefits. At particularly low moisture levels, the castings’ aggregates may begin to collapse and product will be lost to dust.

At the other end of the scale, a moisture content higher than 60% could allow anaerobic conditions to develop during storage, particularly if the vermicast is bagged in polythene. Remember that the more moisture in vermicast, the less air. You need to strike the right balance. At the right moisture level, worm castings will flow and can be spread easily without clogging a fertiliser spreader. (Clogging of trommel screens can be avoided by fitting friction-driven brushes of the type used by street- sweeping machines see photograph 24.)


(loss of weight on ignition)

Indicates organic content of the product, since only organic matter (microflora and  microfauna) is destroyed and gasified therefore

lost on ignition. Assists in detecting any product adulteration and, if this has occurred, the type of adulteration.


Worm castings should be able to provide some mineral plant nutrition. This mineral portion will be present in the residue after ignition. If the product has been adulterated by the addition of sand, for example, LOI will not be great because all of the heavy sand will remain. Alternatively, if sawdust has been used, LOI will be substantial.


(colony forming units)

Indicates the microbial content before packaging and so the potential biological dynamism.

> 5 000 000/gram dry weight

This measure is not a constant and may reduce during storage. While living CFUs reduce during prolonged storage, many leave spores at or near death, which become animated when exposed to moisture, oxygen and warmth.  (This measurement can ony be found by a laboratory).


(foreign matter content)

Indicates presence of material thatis not useful and should not be there, which is increasing the weight of the product.


< 0.5% dry weight

FM is material that will not reduce to its components within a reasonable time. Although originally organic, plastics are included as foreign matter. Other examples that might be found in worm castings are glass particles, mortar, brick chips, gravel, clay.



Quality standard


Plant propagules

Indicates that the product has not been bioremediated or pasteurised.


A propagule is usually regarded as a fertile weed seed, but a weed is simply a plant in the wrong place. So, in worm castings, any shoot or rootling is a weed. Worm castings are frequently used as a basis for potting or seed-raising mixtures. Customers do not want seeds other than those intended germinating in their pots or gardens.

Also, weed seeds in vermicast can be transported across the country from areas in which they are profligate into areas in which they are unknown. The potential environmental damage is frightening.

Plant and animal pathogens

Indicates that the product has not been bioremediated or pasteurised.

Nil (by analysis for specifics)

Plant and animal pathogens can be tested for only by nominating a specific organism and then testing for it using the appropriate test. Testing of a general nature is not practical; you need to know what you’re looking for.

Some animal pathogens (such as Legionella and Salmonella) can cause severe sickness and even death in humans. Others have a similar effect on animals. Some that have not yet been researched (anthrax, for example) may travel in manures and survive vermitreatment.   Plant pathogens may similarly survive and be transferred from one part of the country (in which they thrive) to another part (in which they are previously unknown or rare). Severe and lasting environmental damage is a possibility and there are also potential legal consequences.

A high proportion of pathogens are destroyed by the aerobic conditions in vermicast and antibiotics produced in the process. Most known residual pathogens that we know of are destroyed during pasteurisation. It is extremely important that worm castings receive either pre-vermitreatment bioremediation or post- vermitreatment pasteurisation. Remember that the treatment carried out closest to point of sale is the safest.


(potential hydrogen)

Determines acidity or alkalinity.

As close to neutral (pH 7) as possible, to support the maximum biota population pH 6.5

is ideal

A pH higher than 7.5 or lower than 5.5 suggests the vermicast may have been adulterated.



Quality standard



(electrical conductivity)

Determines salt content.

1.0–1.5 dSm/m (decisiemens per metre) maximum

Because vermicast is often used and recommended as a basis for germinating and seed-raising mix, the low-salt quality standard must be strictly applied, as many seedlings and potted plants are salt-intolerant. Vermicast with a high EC cannot be sold as pure vermicast. The castings may have been adulterated by nitrogen or the deliberate addition of a manufactured fertiliser such as urea.

NOTE: ‘Salt’ does not refer only to NaCl (sodium chloride, or table salt) and a high EC does not necessarily mean the vermicast is unusable. A high EC indicates that further analysis should be carried out to determine exactly what the salts are especially the chloride content. Many salts (ammonium sulphate, for example) are actually plant-benevolent in low concentrations.

And castings adulterated by nitrogen or urea might still be suitable for applications other than germinating and seed-raising mix in some potting mixes, for example.

General appearance

At a moisture level of 40–50%, vermicast should be dark-grey to black in colour, and in aggregate form. Close inspection

should reveal the general absence of fertile capsules and worms. Compressed in a bag, it should exhibit an elastic property;

a handful squeezed firmly in your first should not remain as a reproduction of your fist upon release, but should break up as it falls away. If it retains a fist-shape, the product is free   of aggregates and not genuine worm castings. Aggregates

at a moisture level of 50% or less will flow freely, making soil application easy for the customer.