Soak a 5-gallon bucket and its lid in 9 parts water and 1 part bleach for 20 minutes disinfecting it.
Add 2 gallons of sphagnum peat moss to the clean bucket.
Pour 1 gallon of perlite and 1 gallon of vermiculite over the peat moss. You have the option of using just one or the other. Vermiculite is the better alternative, as it holds nutrients and moisture more efficiently than perlite. You need 2 gallons if you use only perlite or vermiculite.
Blend the potting-mix ingredients with your hands until they are evenly distributed.
Closing the bucket keeps the soil from becoming contaminated in storage. Fill pots with your homemade potting mix as needed. Moisten the blend before planting in it.