Vermicomposting Guide H-164 NMSU

Cooperative Extension Service
College of Agriculture and Home Economics
NEW MEXICO STATE UNIVERSITY

Vermicomposting  Guide H-164

George W. Dickerson, Extension Horticulture Specialist
This publication is scheduled to be updated and reissued 3/04.
1 For more information on composting, see Backyard Composting (nmsu) Extension Guide H-110). Request this publication by calling (505) 646-3228.
You can download this and other publications from our World Wide Web site at http://www.cahe.nmsu.edu. Click on Resources, then Gardeners.
Yard and food waste make up a major component
of solid waste in most municipalities throughout the
United States. Although much of this organic waste
can be recycled in the backyard using traditional aerobic
backyard composting techniques, these techniques
are not appropriate for apartment dwellers and are often
inconvenient, particularly during bad weather in
the winter.1
Vermicomposting, or composting with earthworms,
is an excellent technique for recycling food waste in
the apartment as well as composting yard wastes in
the backyard. Worm bins located near a hot water
heater in the garage during the winter will save many
a trip through the snow to the backyard compost bin.
Letting worms recycle your food waste also saves
your back, because you don’t have to turn over the
compost to keep it aerated.
TYPES OF EARTHWORM
The most common types of earthworms used for
vermicomposting are brandling worms (Eisenia
foetida) and redworms or red wigglers (Lumbricus
rubellus). Often found in aged manure piles, they generally
have alternating red and buff-colored stripes.
They are not to be confused with the common garden
or field earthworm (Allolobophora caliginosa and
other species).
Although the garden earthworm occasionally feeds
on the bottom of a compost pile, they prefer ordinary
soil. An acre of land can have as many as 500,000
earthworms, which can recycle as much as 5 tons of
soil or more per year.
Redworms and brandling worms, however, prefer
the compost or manure environment. Passing through
the gut of the earthworm, recycled organic wastes are
excreted as castings, or worm manure, an organic material
rich in nutrients that looks like fine-textured
soil.
WHAT IS VERICOMPOSTING?
Vermicompost contains not only worm castings,
but also bedding materials and organic wastes at various
stages of decomposition. It also contains worms at
various stages of development and other microorganisms
associated with the composting processing.
Earthworm castings in the home garden often contain
5 to 11 times more nitrogen, phosphorous, and
potassium as the surrounding soil. Secretions in the
intestinal tracts of earthworms, along with soil passing
through the earthworms, make nutrients more
concentrated and available for plant uptake, including
micronutrients.
Redworms in vermicompost act in a similar fashion,
breaking down food wastes and other organic
residues into nutrient-rich compost. Nutrients in
vermicompost are often much higher than traditional
garden compost (see table 1).
Table 1. Chemical characteristics of garden compost
and vermicompost, 1994.
Parameter* Garden compost1 Vermicompost2
pH 7.80 6.80
EC (mmhos/cm)** 3.60 11.70
Total Kjeldahl nitrogen(%)*** 0.80 1.94
Nitrate nitrogen (ppm)**** 156.50 902.20
Phosphorous (%) 0.35 0.47
Potassium (%) 0.48 0.70
Calcium (%) 2.27 4.40
Sodium (%) < .01 0.02
Magnesium (%) 0.57 0.46
Iron (ppm) 11690.00 7563.00
Zinc (ppm) 128.00 278.00
Manganese (ppm) 414.00 475.00
Copper (ppm) 17.00 27.00
Boron (ppm) 25.00 34.00
Aluminum (ppm) 7380.00 7012.00
1Albuquerque sample 2Tijeras sample
*Units- ppm=parts per million mmhos/cm=millimhos per centimeter
** EC = electrical conductivity is a measure (millimhos per centimeter) of the
relative salinity of soil or the amount of soluble salts it contains.
*** Kjeldahl nitrogen = is a measure of the total percentage of nitrogen in the
sample including that in the organic matter.
**** Nitrate nitrogen = that nitrogen in the sample that is immediately available
for plant uptake by the roots.
Guide H-164 • Page 2
Finished vermicompost should have a rich, earthly
smell if properly processed by worms. Vermicompost
can be used in potting soil mixes for house plants and
as a top dressing for lawns. Screened vermicompost
combined with potting soil mixes make an excellent
medium for starting young seedlings. Vermicompost
also makes an excellent mulch and soil conditioner
for the home garden.
ANATOMY OF EARTHWORMS
The earthworm has a long, rounded body with a
pointed head and slightly flattened posterior. Rings
that surround the moist, soft body allow the earthworm
to twist and turn, especially since it has no
backbone. With no true legs, bristles (setae) on the
body move back and forth, allowing the earthworm
to crawl.
The earthworm breathes through its skin. Food is
ingested through the mouth into a stomach (crop).
Later the food passes through the gizzard, where it is
ground up by ingested stones. After passing through
the intestine for digestion, whats left is eliminated.
Earthworms are hermaphrodites, which means they
have both male and female sex organs, but they require
another earthworm to mate. The wide band (clitellum)
that surrounds a mature breeding earthworm
secretes mucus (albumin) after mating. Sperm from
another worm is stored in sacs. As the mucus slides
over the worm, it encases the sperm and eggs inside.
After slipping free from the worm, both ends seal,
forming a lemon-shape cocoon approximately 1/8
inch long. Two or more baby worms will hatch from
one end of the cocoon in approximately 3 weeks.
Baby worms are whitish to almost transparent and are
1/2 to 1 inch long. Redworms take 4 to 6 weeks to become
sexually mature.
HOW TO CONSTRUCT A WORM BIN
Bins can be made of wood or plastic, or from recycled
containers like old bathtubs, barrels, or trunks.
They also can be located inside or outside, depending
on your preferences and circumstances.
As red wigglers tend to be surface feeders, bins
should be no more than 8 to 12 inches deep. Bedding
and food wastes tend to pack down in deeper bins,
forcing air out. Resulting anaerobic conditions can
cause foul odors and death of the worms.
The length and width of the bin will depend on
whether it is to be stationary or portable. It also depends
on the amount of food waste your family produces
each week. A good rule of thumb is to provide
one square foot of surface area per pound of waste in
your bin.
Wooden bins have the advantage that they’re more
absorbent and provide better insulation. Do not use
redwood or other highly aromatic woods that may kill
the worms. Plastic tends to keep the compost too
moist. Plastic, however, tends to be less messy and
easier to maintain. Be sure containers are well cleaned
and have never stored pesticides or other chemicals.
Drilling air/drainage holes (1/4- to 1/2-inch diameter)
in the bottom and sides of the bin will ensure
good water drainage and air circulation. Place the
bin on bricks or wooden blocks in a tray to catch excess
water that drains from the bin. The resulting
compost tea can be used as a liquid fertilizer around
the home landscape.
Each bin should have a cover to conserve moisture
and exclude light. Worms prefer darkness. Bins can
be covered with a straw mulch or moist burlap to ensure
darkness while providing good air ventilation.
Outside bins may require a lid to exclude scavengers
and other unwanted pests.
Outdoor bins should be insulated from the cold to
protect the worms. One option is to dig a rectangular
hole 12 inches deep and line the sides with wooden
planks. The bottomless box can then be filled with
appropriate bedding material, food wastes, and
worms. Food wastes can be continually added as
they accumulate. The pile should be kept damp and
dark for optimum worm activity. During the winter,
soil can be piled against the edges of the bin and
straw placed on top to protect the worms from cold
weather. Do not add food waste to outdoor bins during
the winter because this could expose the worms
to freezing weather.
BEDDING MATERIALS
Bedding for bins can be made from shredded newspapers
(non-glossy), computer paper, or cardboard;
shredded leaves, straw, hay, or dead plants; sawdust;
peat moss; or compost or aged (or composted) manure.
Peat moss should be soaked for 24 hours in water,
then lightly wrung out to ensure it is sufficiently
moist. Grass clippings should be allowed to age before
use because they may decompose too quickly,
causing the compost to heat up. Bedding materials
high in cellulose are best because they help aerate the
bin so the worms can breathe. Varying the bedding
material provides a richer source of nutrients. Some
soil or sand can be added to help provide grit for the
worms digestive systems. Allow the bedding material
to set for several days to make sure it doesn’t heat up
(and allow to cool before adding worms).
Guide H-164 • Page 3
The bedding material should be thoroughly moistened
(about the consistency of a damp sponge) before
adding the worms. Fill the bin three-quarters full of
moist bedding, lifting it gently afterwards to create air
space for the worms to breathe and to control odors.
ADDING THE WORMS
Under optimum conditions, redworms can eat their
own weight in food scraps and bedding in one day.
On the average, however, it takes approximately 2
pounds of earthworms (approximately 2,000 breeders)
to recycle a pound of food waste in 24 hours. The
same quantity of worms requires about 4 cubic feet of
bin to process the food waste and bedding(1 cubic
foot of worm bin/500 worms).
Composting worms can be purchased from dealers
listed in the ad sections of many garden magazines.
Some dealers sell worms as pit-run worms, which
consist of worms of all ages and sizes. Add worms
to the top of the moist bedding when they arrive.
The worms will disappear into the bedding within a
few minutes.
ADDING FOOD WASTE
Earthworms eat all kinds of food and yard wastes,
including coffee grounds, tea bags, vegetable and fruit
waste, pulverized egg shells, grass clippings, manure,
and sewage sludge. Avoid bones, dairy products, and
meats that may attract pests, and garlic, onions, and
spicy foods. Limited amounts of citrus can be added,
but too much can make the compost too acidic. The
compost should be kept at a pH of 6.5 if possible,
with upper and lower limits at 7.0 and 6.0, respectively.
Overly acidic compost can be corrected by
adding crushed eggshells.
Avoid adding chemicals (including insecticides),
metals, plastics, glass, soaps, pet manures, and oleanders
or other poisonous plants, or plants sprayed with
insecticides to the worm bin.
Food wastes should be added to the bin by pulling
back the bedding material and burying it. Be
sure to cover it well to avoid attracting flies and
other pests. Successive loads of waste should be
buried at different locations in the bin to keep the
food wastes from accumulating. Grinding or blending
the food waste in a food processor speeds the
composting time considerably.
CONTROLLING TEMPERATURE AND
MOISTURE IN THE BIN
Redworms can survive a wide range of temperatures
(40-80°F), but they reproduce and process
food waste at an optimum bedding temperature
range of 55-77°F. The worms should never be allowed
to freeze. Bins kept outside may have to be
insulated with straw in the winter to keep the
worms from freezing. Portable bins can be kept by
a hot water heater in the garage during the winter to
keep them warm.
The bin contents should be kept moist but not
soaked. Do not allow rainfall to run off a roof into the
bin. This could cause the worms to drown. A straw
covering may be needed in exposed sites to keep the
bin from drying out during hot summer weather.
MAINTAINING THE BIN
Food scraps can be continually added to the bin for
up to 2 to 3 months, or until you notice the bedding
material disappear. When the bedding disappears, harvest
the worms and finished compost, then refill the
bins with new bedding material.
Overloading the bin with food wastes can result in
foul odors. If you notice these odors, stop adding the
waste until the worms have a chance to catch up.
Overly moist food waste and bedding also cause
odors. To relieve this problem, fluff up the bedding to
add air and check the drainage holes. As a general
rule of thumb, keep the bedding material moist, but
never soggy. Make sure the food waste is buried properly
in the bedding. Exposed food wastes can attract
fruit flies, house flies, and other pests. Keeping the
bin covered with straw or moist burlap also deters
these pests.
Garden centipedes can be a problem in the worm
bin, especially outside. These predators should be destroyed.
Overly wet beds also can attract the earthworm
mite, which may cause the worms to stop eating.
HARVESTING THE COMPOST AND WORMS
There are three basic ways to separate the worms
from the finished compost. One way involves moving
the finished compost and worms over to one side of
the bin and adding new bedding material and food
waste to the other side. Worms in the finished compost
should move over to the new bedding with the
fresh food waste. The finished compost can then be
removed.
Guide H-164 • Page 4
A second way to remove the worms is to build a
small harvester frame of 2 x 4s with a 3/16-inch mesh
bottom. Place the worm compost on the frame and sift
the worms out. Larger pieces of compost can be returned
to a new batch of bedding and worms.
The compost also can be placed in small piles on a
tarp in the sun (or under bright lights inside). Because
worms don’t like light, they will wiggle to the bottoms
of the piles. After waiting 10 minutes, remove
the upper inch or more of finished compost from each
pile until you run into the worms. Allow the worms to
again wiggle to the bottom of the pile and repeat the
process. Combine whats left of the small piles into
one big pile and again repeat the process. You should
eventually end up with a pile of finished compost and
New Mexico State University is an equal opportunity/affirmative action employer and educator. NMSU and the U.S. Department of
Agriculture cooperating.
Reprinted June 2001 Las Cruces, NM
5C
a ball of worms. The worms can be added back to a
new bin of bedding and food waste. Larger worms
also can be used as bait for fishing.
REFERENCES
Appelhof, Mary. 1982. Worms Eat My Garbage.
Flower Press, Kalamazoo, Michigan. 100 p.
Martin, Deborah L. and Gershung, Grace. 1992. The
Rodale Book of Composting. Rodale Press,
Emmaus, Pennsylvania. 278 p.
Shields, Earl B. 1982. Raising Earthworms for Profit.
Shields Publications, P.O. Box 669, Eagle River,
Wisconsin. 128 p.
To find more resources for your home, family, or business, visit the College of Agriculture and Home Economics on the World Wide Web
at http://www.cahe.nmsu.edu.