Design and Construction of My Worm Bin, Original post 4/13/11, Edited 7/28/12

Design and Construction of My Worm Bin

Original Post 4/13/11

Last Edited 7/29/12

Materials and tools to construct:

Ten Gallon Sterilite plastic tote

Cheapest  1 inch X 3 inch strapping you can buy. One 8 ft piece is enough for one bin.  I use four pieces the short way on top cut 10 1/2 inches and two pieces cut 13 ¼ inches the long way underneath.  I use hot melt glue and screws to hold the base together.

Plastic Window screen material to cover the base

Hot melt glue to hold window screen to wooden base

One inch metal putty knife to spread hot melt glue

Heat gun to heat metal putty knife to facilitate spreading of hot melt glue

I cut a piece of window screen to cover the base and hold it in place with hot melt glue.  I heat the metal putty knife with the heat gun in order to spread the hot melt glue.

Row Cover to cover bin, I use All Purpose Fabric, from Gardener’s Supply Co. Item 32-646.  It comes in 6 ft by 20 ft  piece – enough for 24 bins.

One inch wide nylon strap material, 50 inches long, cut in half

One inch wide elastic strap material, 9 inches long, cut in half

Lots of old news paper, don’t use the glossy inserts

Construction:

Construct base to fit in the bottom of tote and cover with the fiberglass screen.  I use four pieces of strapping the short way on top and two pieces the long way underneath.  I use hot melt glue and screws to hold the base together.  I use Hot Melt Glue to hold the screen in place -- no tacks.

I cut a piece of cardboard by trial and error to fit the bottom of the bin and then use this as a template to mark the base to trim it to fit.  I use the same template to mark and cut the screen for the base.

Plug the holes near the handles with masking tape or
Gorilla Tape.  

Cut piece of row cover the size of the lid – use lid to draw outline on the row cover and then cut leaving four inches to spare all the way around.

Make belt from nylon strap and elastic: My wife makes these “belts” by cutting two pieces of the nylon strap 25 inches long and two pieces of elastic material 4 ½ inches long.  She sews the four pieces of material together with a slight overlap at the seams resulting in a belt that is 56 ¼ inches around when relaxed and stretches to 61 ½ inches when fitted around the top lip of the bin.  This tension provides the seal which keeps insects inside or those outside from getting in.  If the strap is too loose the seal is inadequate to keep insects in and if it is too tight it is very difficult to put the belt on the bin.

Why?

Ventilation and air circulation help reduce condensation inside the bin.  Getting rid of the moisture that is a byproduct of the vermiculture process is very important.  The vermiculture should stay moist and the castings should be crumbly – NOT muddy.  The air space under the base helps too. 

Worms need air to breath; they absorb oxygen through their skin.  And air promotes aerobic decomposition which is the “good” kind.  Anaerobic decomposition (without air) produces nasty smells.  The row cover provides more than enough ventilation.

Drain – I have eliminated the drain which came with the original bin.  It was there to drain off excess “tea” that accumulated in the space under the base.  The drain leaked.  Also I have changed my method of getting rid of the excess moisture which has eliminated the need for a drain.  

Base – The base is to support the bedding and allow excess moisture to accumulate below the bedding.  Otherwise the bottom of the bin would get soggy wet and so would the vermiculture in that area.  Wet muddy vermiculture is to be avoided.  There is less air in a wet environment and can result in anaerobic (lacking oxygen) decomposition which smells awful.  We want aerobic (in the presence of oxygen) decomposition.

Row Cover over top of bin and all holes plugged – to keep resident flies inside the bin until captured in the fly trap or on the Fly Paper and to exclude visiting  flies that are attracted by the smell of good food. These visitors would lay their eggs if given a chance.  With the fly trap and or Fly Paper installed inside the bin there will be few if any flies inside the bin under normal conditions.

I have 25 worm bins in my cellar covered as described and we don’t have a problem with flies in the cellar.  

My Worm Bin, Original post 4/13/11, Last Edited 2/22/15

My Worm Bin

Original Post 4/13/11

Last edited 7/29/12
Last edited 2/22/15

Ten gallon plastic tote from Wal-Mart, Sterilite Brand, cost about $5.

A wooden base in the bottom covered with window screening material provides air space under the bedding and a space to collect excess moisture.

I eliminated the drain – more on that later.

Several dry folded newspapers to act as a sponge to soak up excess moisture.

Shredded news paper strips that have been dampened make up the next layer.  This is the layer that the worms live in and in which you bury your food scraps.  It is also where the worm castings accumulate as the worms do their thing.

Dry shredded news paper strips on top of bedding to absorb excess moisture.

A layer of folded dry newspaper on top.

Screened vents in the top of the sides.

Edit: 7/29/12: I have eliminated the screened vents and instead use a piece of garden row cover to cover the top of the bin and hold it in place with a one inch wide nylon strap with an elastic piece sewn in.  The tension in the strap holds the row cover on tight. The row cover provides plenty of ventilation and does a better job of keeping flying insects out of the bin (or ones in the bin from flying out).  Particularly, this has solved a problem I had with fungus gnats infesting the bin.  The fungus gnats could access the bin through the screened vents.

I purchase the row cover from Gardener’s Supply Co. Item 32-646, All Purpose Fabric, 6ft X 20ft – enough for 24 worm bin covers.

Screened vents in the lid.

Edit: 7/29/12: The lid has been replaced with row cover.  I also lay a couple sheets of folded newspaper on top of the row cover to retard drying if the bin seems to be drying out.  

A baited Fly trap to capture fruit flies.

Edit: 7/29/12: If fruit flies are a problem then continue to use the baited fly trap.  I have had more trouble with fungus gnats and another small fly identified as a Minute Black Scavenger Fly which looks a lot like a fungus gnat.  They are not attracted to the vinegar bait in the fly trap.

New 7/29/12: A strip of TAT Fly Paper to trap flying insects inside the bin.

To trap flying insects inside the bin I use a strip of TAT Fly Paper unrolled from its container and stuck to a sheet of dry newspaper that is put in the top of the bin under the row cover.

Stick the bins if you stack them to allow ventilation.

Edits 2/22/15: 
I have eliminated the screened material on the top of the wooden base.  The newspaper on the top of the wooden base provides it own support.  I use 2 pounds of folded newspaper on top of the wooden base to absorb the excess moisture from the vermicompost.  I change the newspaper every 3 to 4 months when I harvest the worm bin.  I tear up the old wet base paper and use it as bedding when needed.

I keep the bin filled to within 3 to 4 inches of the top with moistened newspaper torn into strips (the bedding.)  The worms and microbes digest the bedding during the 3 to 4 months between harvests.  Adding bedding material helps keep the vermicompost from compacting and turning anaerobic.

I use a plastic storage bag or plastic shopping bag over the top of the vermicompost to help keep the top from drying out.  In the winter the air is very dry and the top of the bin will dry out unless evaporation is retarded.  The plastic works well.  In the summer when the humidity is higher the plastic cover has to be removed or reduced in area to prevent the vermicompost from getting too wet. 

Worm Bin Checklist to Hand Out to New Worm Bin Owners

Worm Bin Checklist to Hand Out to New Worm Bin Owners

Updated 12-20-2011

Feeding:

Feed the worms scraps from the kitchen including fruit and vegetables, old bread, cereal and anything of plant origin.  This includes paper.  Tearing it up or chopping it up speeds the process but is not necessary.  Start with one pint buried in the front of the bin and then a second pint buried in back a few days later.  Check the front after a week and only add once most of the food is consumed (looks like dirt instead of garbage.) How soon you can feed again will depend on the temperature, the nature of the feed, the moisture, and number of worms.  One pound of worms should consume about ½ pound per week of garbage.  If you feed too much then the worms can’t keep up and the garbage may heat up and or decompose anaerobically (without oxygen -- which smells bad.)  Potato peels, orange peels, carrots, avocado skins, corn cobs take a long time to decompose but they will eventually disappear.  Softer foods disappear quickly.  Make your judgment when to feed next based on the softer foods.

Moisture control:

Not too dry, not too wet.  70% moisture is the target but the worms are tolerant of both wetter and drier conditions.  When there is too much moisture they may try to escape the bin.  You also run the risk of the bin going anaerobic (without oxygen) and getting smelly.  A wet bin at the bottom is to be avoided.  Add dry newspaper to help take up excess moisture.  If the vermiculture is too dry, spray water on top of the vermiculture to add water. Use “Squeeze Test” to measure.  Worms breathe through their skin which must be moist in order for them to breathe.

Squeeze Test to judge moisture:

Take a handful of the vermiculture or the wet newspaper and squeeze it as hard as you can.  If you can just see a little moisture coming out from between your fingers the moisture is perfect.  If you can wring water out of the vermiculture then it is too wet.  If no liquid moisture can be seen then it is too dry.

Temperature:

Not too hot, not too cold.  Ideal temperature is 68F for feeding and reproduction.  Worms will die if they freeze.  They will die if they get too hot – 90 to 95F is the upper limit.  If you keep them in an environment between 50 and 75F they will do OK.  In the summer they can be kept outside in the shade but need to be checked for overheating on very hot days.  Too much food all at once may decompose thermophilically and heat up the bin locally to 80F or 90F or more.  If this happens, the worms will move away to a cooler spot in the bin until things cool off and then they move back to eat the decomposed garbage.

Insect Control:

Use TAT Fly paper stuck to a folded sheet of newspaper in the top of bin to measure and trap the insects.  If an infestation occurs, cover the side vents with masking tape and put row cover over the top of bin held in place with nylon strap with elastic gusset to trap adults inside.  Fruit flies can’t pass through the screened vents but Fungus Gnats can.  The adult insects will eventually be trapped on the fly paper and the infestation will be controlled.

If the infestation is fruit flies, then adding the fruit fly trap too would be advantageous since it will actively attract the adult flies while the fly paper is just a passive trap.  Fungus gnats and short flies are not attracted to the vinegar in the fruit fly trap.

Harvest:

Harvest worm castings from the bin to use on house plants or garden.  They contain nutrients as well as natural plant growth hormones and disease fighting chemicals.  The use of worm casting up to 40% in plant soil has shown improved growth and harvest as well as more plant vigor and disease and pest resistance.  Make worm tea from castings as a convenient way to feed house plants.  Worm tea is just as good as the castings.

Worm Tea:

This is made from worm castings.  Harvest the worm castings from the bin.  In a five gallon bucket put one pound of worm castings into 4 gallons of water.  Put a fish tank bubbler into the bucket to add air and stir the mixture occasionally.  (I use a paint stirrer on an electric drill but that isn’t necessary.)  After 12 hours add 1 TBS of molasses and stir and bubble for another 12 hours. When done strain the mixture through a sieve into a watering can and apply the tea to house plants or to plants in the garden.  It can also be sprayed on the foliage.  It can be used as is or diluted 50:50 with water.  It will not burn plants.  This is a living culture and needs to be made fresh each time.

If you have insect pests in your bin ( i.e. fungus gnats) then using worm tea on house plants is preferable since the insects won’t be transferred to the house plants as they would be if you used the castings. (The castings contain the insect larva.  The tea does not.)

Q&A

How much food can I expect one bin to handle? 

One mature ten gallon tote has about 2 pounds of worms when it reaches maturity in about 4 to 5 months.  The worms will process about 1 ½ pounds per bin per week.  Starter bins that have one pound of worms to start consume about ½ pound per week.  These results vary with temperature, moisture,  and the feedstock.

How long can I leave them without feeding?

Leaving them for a couple weeks is of no concern.  If you leave them for months without fresh food the worm population will gradually decrease and the worms will get smaller.  They will stop reproducing.  The worms will process everything in the bin over and over until there is nothing left but castings.  In a bin that I left for several months this way there were still a few small worms. 

Where is a good place to keep worms?

I keep mine in the cellar where it is about 65F year round.  A cellar that is at least 55F will work but the worms will not eat as quickly or reproduce as quickly if they were warmer.  Keeping them in your living space requires that you do a good job controlling insects.  Fruit flies, fungus gnats and short flies are all nuisance insects that would like very much to have access to your worm bin for feeding, breeding and egg laying.

If you already compost what advantage is there to having a worm bin?

For one thing the convenience of having the worm bin in the house in the winter justifies it.  The worm bin can be used in the winter as a source of castings to make worm tea for house plants or seedlings.  My wife and I grow greens in the basement under a grow light in the winter for salads.  The worm castings and worm tea are used to feed these plants.  The worm castings produced by the worms during the winter are ready to be used to plant in the spring.  Also worm castings are superior to compost for seed germination, plant growth, vigor, disease and pest resistance and harvest.  Use up to 40% with potting soil or garden soil for best results.  Even as little as 5% produces measureable results.