| August 17,
2004: A variety of commercial vermicompost systems
are available for purchase; but you can easily build your own
for less. The term vermicomposting simply refers to composting
organic matter with worms. Vermicompost, the end product,
is a high-nutrient form of compost containing nitrogen, phosphorous,
potassium, calcium, sodium, magnesium, iron, zinc, manganese,
copper, boron, and aluminum. These nutrients are often more
abundant and more readily available to plants in vermicompost
than in other types of compost. In addition, vermicompost
can benefit your soil by improving its structure and porosity.
Preparing the bin
The vermicompost bin will consist of two, 10-gallon Rubbermaid
(or similar) containers stacked on top of each other, with
a third bin being added later on. Holes, one half-inch in
diameter, will be drilled into the upper sides and bottom
of the top bin (which will contain the bedding) to allow for
aeration and drainage.
The bottom bin will be used to catch leachate drainage, materials
falling out through the holes, and escaping worms. When the
material in the initial bin has been sufficiently processed,
a third bin with fresh bedding is added on top. The worms
will migrate up through the holes to the fresh material, leaving
behind vermicompost in the bottom bin to be harvested.
Preparing the bedding
Bedding is necessary for worms to burrow, bury food scraps,
and also for moisture retention. Bedding material must be
a non-toxic, fluffy material that holds moisture and allows
air to circulate. Popular bedding materials include shredded
newspaper, computer paper, decaying leaves, grass clippings,
peat moss, or some mixture of the above.
Our own bedding consists of a mixture of peat moss (approximately
3.0-3.5 lbs dry) and one of the following: chopped wheat straw,
shredded newspaper, or dried coffee bean hulls (approximately
0.65 lb dry). Dry bedding materials are mixed and slowly wetted
with approximately 10 liters (2.6 gallons) of distilled water,
mixing the materials as the water is added. Once worms are
added to the bedding, the moisture level should remain approximately
that of a wrung-out sponge.
Worms
The best composting worms are red wigglers (Eisenia foetida)
which can be obtained from a local bait shop or through mail
order. Generally, they cost about $20 a pound, not including
any shipping fees. Regular garden and compost worms will not
survive in worm bin conditions and therefore should not be
used.
Red wigglers can typically consume about a half-pound of
food scraps per one pound of worms in a 24-hour period (one
pound of worms equals roughly 1,000 worms). You can adjust
your bin size and worm population to accommodate your food-scrap
load. Keep in mind that in about two weeks the worms will
begin reproducing, increasing the population. One pound of
worms should be a good starting population for the 10-gallon
bin.
Once you have your worms, place them on top of the moistened
bedding and they will quickly burrow in.
Feeding
Worms eat all kinds of food including coffee grounds, tea
bags, vegetable and fruit scraps, egg shells, and yard waste.
Worms are known to particularly enjoy broccoli, watermelon,
cantaloupe, and pumpkin.
It's best to avoid bones, dairy products, meats, garlic,
onions, and spicy foods. Citrus foods should also be avoided
as they can cause the bin environment to become too acidic
(an over-acidic bin can be corrected by adding crushed eggshells).
To speed the decomposition process, food should be chopped
or shredded before being added to the bin.
To feed, pull back the bedding, put in the food scraps, and
then re-cover with bedding. This will minimize mold, flies,
and other pests.
Where to put the bin?
The main concern when deciding on a location for your worm
bin is temperature. The ideal temperature for red wigglers
to grow in is 55-75? F. Popular indoor spots include the kitchen,
garage, laundry room, or basement. If you want to keep your
worm bin outdoors, you must shade it in the summer and insulate
it in the winter (with hay bales or other material) to maintain
the proper temperature range. Also, if your bin is outdoors
remember to protect it from flooding conditions as worms can
easily drown inside the bin.
Harvesting vermicompost
You can harvest vermicompost after about three months. To
do this, prepare your second bin of fresh moist bedding exactly
as you did the first. Place the second bin on top of the first,
making sure that the holes in the bottom of the second bin
are flush with the surface of the bedding in the first bin
(worms cannot crawl through air).
The worms will then begin to migrate up to the new bin, leaving
behind vermicompost. From our experience, the process may
take up to two weeks, and adding fresh food scraps to the
new bin will encourage the migration.
Harvested vermicompost can be added to potting mix or garden
soil to provide an excellent source of readily-available plant
nutrients and organic matter.
As long as you maintain a healthy worm-bin environment (i.e.
proper temperature, moisture, pH, and food), the worm population
will stabilize itself and there will be no need to either
purchase additional worms or remove surplus worms.
Happy vermicomposting!
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