Quick Facts...
- Vermicomposting uses a specific type of earthworm that works with
other compost organisms to decompose manure and bedding.
- Earthworms breathe through their skin and must be in an environment
that has at least 40 percent moisture (at least as damp as a wrung out
sponge).
- Worm excrement is commonly called castings.
- Worms can double their population every four months under ideal conditions.
What is Vermicomposting?
The prefix “vermi” is Latin for worm. Vermicomposting refers
to the utilization of the digestive process of earthworms to make compost.
Vermicomposting uses specific types of earthworms (e.g., red worms, tiger
worms, red wigglers) that work with other compost organisms to decompose
manure and bedding.
Is Windrow Vermicomposting Right for My Operation?
Advantages
- Minimal aeration of the windrow is necessary; therefore, labor
and
equipment costs are reduced.
- Supplemental nitrogen is not needed so there are no nitrogen costs.
- Worm castings (worm feces) improve plant growth over windrow compost.
- Under ideal conditions red worms double their population every
four months.
Disadvantages
- Initial cost of red worms (up to $12 per pound for bulk orders
plus shipping) may be cost prohibitive.
- Monitoring and caring for red worm population year round.
- Decomposition depends upon the number of red worms in the windrow.
- The market is less developed for worm castings than it is for regular
compost.
- This technique may not kill weed seeds or parasites.
What Types of Earthworms are Used?
There are three types of earthworms:
1. Anecic (Greek for “up from” or “out
of the earth”)
- Builds permanent burrows into the deep mineral layers of the soil.
- Drags organic matter from the soil surface into their burrows for
food.
- Includes the familiar bait worm–the nightcrawler (Lumbricus
terrestris).
2.Endogeic (Greek for “within the earth”)
- Builds extensive permanent burrows in the upper mineral layer of
soil.
- Feeds on the organic matter in the soil.
- Lives exclusively in soil and usually are not noticed, except after
a heavy rain when they come to the surface.
3. Epigeic (Greek for “upon the earth”)
- Lives on the soil surface.
- Forms no permanent burrows.
- Feeds on decaying organic matter.
- Used for composting and commonly called: red worm, manure worm, brandling
worm, red wiggler, and compost worm (all Eisenia fetida); tiger
worm and red tiger worm (both Eisenia andrei).
In Colorado, both E. fetida and E. andrei have been proven
to withstand near freezing conditions. This makes them the best choice for
outdoor vermicomposting. Often laboratory tests are required to distinguish
the two Eisenia species and because their performance is the same,
the generic name, Eisenia (eye-sen-ee-uh), will be used to refer
to both species throughout this fact sheet.
The Biology of Eisenia
Respiration, Digestion, Excretion, and Reproduction
Earthworms breathe through their skin and must be in an environment that
has at least 40 percent moisture (at least as damp as a wrung out sponge).
If their skin dries out they cannot breathe and will eventually die.
Instead of teeth, Eisenia have a gizzard like a chicken. They
eat bacteria, fungi, other compost organisms and decaying organic matter
small enough to fit into their mouth. In doing so, they can consume close
to their body weight in compost material every 24 hours. However, on average,
they consume half their body weight every 24 hours. To get this rate of
decomposition you must maintain ideal compost conditions, as described
below.
Worm excrement is commonly called castings. While they may look and feel
like tiny flecks of sticky soil, they are full of beneficial soil microbes.
Scientists have yet to conclude exactly why Eisenia castings are
good for plants, but they seem to contain nutrients that plants can easily
use and disease-suppressing microbes. The mucous covering on the castings
also appears to slow down nutrient release. In addition, enzymes in the
gut of Eisenia may kill many pathogens harmful to plants, horses,
or humans that pass through its gut. In any case, castings will not burn
your plants, even seedlings, and they have a neutral pH.
Under ideal conditions, Eisenia can double their population every
three months. They are hermaphroditic (having both male and female reproductive
parts) and become sexually mature when the familiar band (the clitellum)
appears around their body, closer to their mouth. Each worm with a clitellum
is capable of producing four cocoons per week containing, on average,
two baby worms each.
Environmental Requirements
Eisenia tolerate temperatures from 39 to 90 F. Their ideal range
is 65 to 75 F. They tolerate moisture levels from 40 to 100 percent but
prefer 60 to 80 percent. Eisenia tolerate a pH range of 2 to 9,
preferring a range of 5.5 to 7. Eisenia are sensitive to sunlight
or electric light. Their breathing becomes depressed after as little as
five minutes of light exposure. At this point Eisenia become confused
and disoriented, making it difficult to find shelter. More than 30 minutes
exposure to sunlight can kill Eisenia. They normally do not live
in densities greater than 1,000 worms per cubic foot of material. Eisenia
search out these desirable conditions in a windrow provided there is a
food source.
Will horse dewormers kill red worms?
The most common wormer used is known by the brand name Ivermectin®
made by the Merial Company. Merial’s research shows that the active
chemicals in Ivermectin® are deactivated when manure is exposed to
sunlight. Equine studies show that 95 percent of the active chemicals
in Ivermectin® are deactivated in the horse before being passed in
the feces. Leading experts in vermicomposting believe that the concentration
of Ivermectin® in the horse manure is not high enough to seriously
injure Eisenia.
How Do I Get Started?
This sheet bases much of its information on fact sheet 1.225, Composting
Horse Manure in Dynamic Windrows. It’s necessary to refer to
that fact sheet in order to understand and implement the information and
methods described herein.
How many Eisenia are needed?
One pound of Eisenia (approximately 1000 worms) will eat approximately
3.5 pounds of material per week. A single horse produces about 350 pounds
of manure per week. So, you will need 100 pounds of Eisenia per
horse to digest each week’s amount of manure. If this manure is mixed
half and half with bedding, you’ll need 200 pounds of Eisenia
per horse. For many, the initial cost of $12 per pound plus shipping makes
this suggested population prohibitive.
The best option for many operations is to start with as many worms as
you can afford, maintain ideal conditions for them, and record doubling
times to calculate when you have a population that can decompose your
amount of manure and bedding. Monitoring your vermicomposting windrow
is the best method for determining how quickly the manure and bedding
are composting. Dig into the windrow and see if the material has been
transformed into castings. With a little practice you will be able to
distinguish bedding and manure from castings. Castings are usually darker
than manure. See Table 1 for ideal pounds of Eisenia required to
digest fresh manure and bedding produced in a week within seven days.
Regardless of the option you choose, request Eisenia that are
“bed run.” These contain worms, castings, bedding, and cocoons.
They will speed the colonization of your windrow and adjust to specific
conditions of your vermicomposting windrow faster.
Example: 50 pounds of Eisenia will reproduce to 1,000 pounds of
worms shortly after four doubling periods (in just over 16 months). In
two years, that initial 50 pounds of Eisenia will be more than enough
(3200 pounds) to vermicompost the manure from 30 horses.
| Table 1: Ideal pounds of Eisenia required
to digest all manure and bedding as it is produced. |
| Number of Horses |
Pounds of Eisenia Required with Manure Only |
Pounds of Eisenia Required with Manure and Beddinga |
| 1 |
100 pounds |
200 pounds |
| 2 |
200 pounds |
400 pounds |
| 5 |
500 pounds |
1,000 pounds |
| 10 |
1,000 pounds |
2,000 pounds |
| 20 |
2,000 pounds |
4,000 pounds |
| 30 |
3,000 pounds |
6,000 pounds |
| 40 |
4,000 pounds |
8,000 pounds |
| a50 percent manure and 50 percent
bedding. |
| + Assumes one pound of worms eats ½
pound of material every 24 hours. |
| ++ Assumes three doublings per year (every
four months is one doubling). |
| +++ Requires that normal weekly volumes
are supplied and not excess from stockpiles. |
How to Set Up the Vermicomposting Windrow
Option 1: Establish the area for the vermicomposting windrow following
the guidelines in fact sheet 1.225, Composting Horse Manure in Dynamic
Windrows, but do not add additional nitrogen to the manure
and bedding. Monitor temperature in the windrow and turn it before
temperatures reach 145 F to prevent carbonizing the material and reducing
its palatability for Eisenia. Eisenia digest material faster
if it has composted for seven to 10 days first.
Create an initial base of material 6 feet wide, 18 inches tall, and 6
feet long. The base should be oriented east/west so it receives sunlight
on its south side all day.
Water this base of material until it feels wetter than a wrung out sponge.
Divide your quantity of worms and distribute them evenly over the top
of the moistened base material. Eisenia should immediately migrate
into the material.
Once the worms have colonized this material, add a 3-inch layer of material
weekly to the start-up pile and moisten appropriately. Add to the pile
gradually to prevent it from heating up and killing the worms.
Since this process should not generate heat, it is advisable to set up
the initial windrow in the summer. A large windrow will be formed during
the season to help retain heat during the winter months.
After the pile reaches a height of 3 feet, add new material to the end
of the pile in the direction that the windrow will be built. It should
match the width of the start-up pile and have a height of 3 feet to allow
for volume reduction. Facilitate the heating of this new material (by
turning and watering) to a maximum temperature of 145 F. Eisenia
will migrate into this new material once it has digested all of the start-up
pile and the new material has cooled below 90 F and has ideal moisture
levels.
Continue lengthening the windrow until you run out of space. At this
point you can make a “U-turn” and advance back in the opposite
direction, parallel to the first windrow.
Option 2: Create a base layer as you would in Option 1 that is
18-inches tall, 6 feet wide and as long as six weekly volumes of material
will allow. Water the material and distribute Eisenia evenly across
this 18 inch tall windrow as you would in Option 1. Allow Eisenia
to colonize this windrow and digest most of the material in the base.
The time required for this will be dependent on the number of Eisenia.
Monitor weekly for moisture and digestion.
Once Eisenia have digested most of the base layer, add a 3-inch
layer of material on top of the base layer down the length of the windrow.
Continue weekly monitoring for moisture and digestion. Create additional
3-inch layers at a frequency determined by how quickly Eisenia
digests the material.
After this first windrow reaches 3 feet in height, begin building the
second base layer parallel to and touching the first windrow as you did
initially. As Eisenia begin colonizing this new base layer, add
your first 3-inch layer to this second windrow. Add more layers as you
notice Eisenia digesting the material.
Warning: Manure and bedding are difficult to wet once they completely
dry out!
Which Option Do I Choose?
Option 1:
Advantages
• Involves less hand labor.
• Eisenia population grows more rapidly.
• Pathogen and weed seed reduction.
Disadvantages
• Digestion is not as thorough.
• There is a greater chance of the windrow becoming dangerously hot.
Option 2:
Advantages
• There is a lesser chance of the windrow becoming too hot.
• Digestion is more complete – more castings.
Disadvantages
• More hand labor involved.
• Eisenia population does not grow as rapidly.
Maintaining the Vermicomposting Windrow
Adding more material to a windrow will be based on how quickly Eisenia
are digesting their current vermicomposting section. Moisture and temperature
management in the windrow dictates where they migrate to or from.
Monitor temperature along the length of the windrow with a compost thermometer
(2 feet long). If temperatures exceed 90 F, open holes along the top of
the windrow to release the heat. Maintaining high moisture levels suppresses
heat-producing microbes, but be careful – too much water will force
air (and worms) out of the windrow.
It may be necessary to cover the windrow with a compost cover to retain
heat during colder periods. Use clear or black plastic films to retain
the windrow’s heat and gain solar heat. Be sure to leave openings
at the ground level to allow for air exchange and to prevent anaerobic
conditions. Higher windrows retain more heat as well, but do not exceed
5 feet in height.
Harvesting the Vermicompost
Allow time for the majority of worms to migrate into the new material
before harvesting castings (keep your worms!). You will need to check
older sections of the windrow to see if the worms have migrated out of
it prior to harvesting. Castings can be tilled into the soil directly
from the windrow or screened for adding to greenhouse soil mixes, potted
plants, lawns, and gardens.
References
- Davis, J.G., and A.M. Swinker. 1996. 1.219, Horse Manure Management.
Colorado State University Extension.
- Rynk, R., et al. 1992. NRAES-54, On-Farm Composting Handbook. Northeast
Regional Agricultural Engineering Service.
- Card, A.B. and J.G. Davis. 2002. 1.225, Composting Horse Manure
in Dynamic Windrows. Colorado State University Extension.
- Card, A.B. and J.G. Davis. 2002. 1.226, Composting Horse Manure
in Static Windrows: Passively Aerated Windrow Method. Colorado State
University Extension.
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