Worm bedding need not be the big secret.  The type of worms you wish to grow will dictate the type of bedding you will need to raise various worms. 

Red Worms-  Red worms require a bedding made of manure and some other type of organic material.  We use 40% peat moss to 60% manure.   We try to use as much rabbit manure as possible in our bedding mixture, but we also use cow, horse and poultry manure.   The important thing to remember with the bedding is that is has to be past the heating stage.  Hot manure (fresh manure) needs to be composted a bit before your bedding is mixed.  Failure to do this will cause the bedding to heat, and your worms may die.  Another great bedding is shredded newspaper or cardboard with manure.   Worms love paper bedding.  Shred the newspaper and then soak it.  After it is soaked let the water drip from it for a couple of minutes and place it in the beds or pits.   Mix in manure  and a you will have your bedding.  There are many different things that can be used for bedding.  If you remember the following you will be able to improvise:

Red worms need moisture at all times.  The more moisture the bigger they will become.  But remember to check the ph level. 

If using grain, top feed your worms.  Many people believe that mixing feed in with the worms will work best.  I have found that top feeding with chicken layer mash works well.  Place in only enough feed for a day or so.  Do not mix the beds until the feed is gone.  This will stop the feed from getting mixed in, and causing the bedding to heat and sour.  Mixing feed into the bedding will cause the bedding to sour.   Sour bedding will kill worms.  Test your soil regularly with commonly bought PH Testers.  These testers are only a couple of bucks, and can be found at many feed and garden centers. Sprinkle pulverized limestone on top of the bedding after watering to control acid.

Africans Nightcrawlers-  Africans like bedding with dirt, and peat, but will only feed on the top.  Bedding for Africans does not have to be deep.  4" is enough.  Use a mix of soil and manure with straw for best results.  Africans need it wet and hot 75 to 90 degrees for best results.  Turn bedding weekly for airration.  African Nightcrawlers cannot tolerate acid.  Just watch the acidity of the soil. Purchase a PH test kit and monitor the soil weekly.  They love rabbit and poultry manure.

Northern / Canadian Nightcrawlers-  These worms are very delicate.  They require top soil bedding and must be surface fed.  the bedding must be moist but not wet.  These crawlers use burrows to live.  Heavy watering will cause them to drown.  Contrary to popular beliefs if you don't disturb these worms and they will breed.   Lightly sprinkle mash, leaves and grass on the top.  45-60 degrees is all they can tolerate any warmer and they will die.  They will do well and breed if kept with these guidelines. We raise these burrowing worms in large 30 to 50 gallon plastic containers that have holes drilled in them to facilitate drainage.

Grey Wigglers-  Grays require a soil that is more course and dense.  A mix of 1/3 leaf mulch, 1/3top soil and 1/3manure works well.   Our experience has shown me that Grays like moist beds and plenty of pulverized lime stone sprinkled on top.   Grays should also be top fed and not disturbed except once a month when you turn the beds over to get air in the beds.  Grays will eat small amounts of layer mash, but prefer leaves and grass clipping.  75-85 degrees for best results

Always remember to use manure that is well aged. with all of the above variations.