Mushrooms contain 30 to 50,000 spores. These spores are minute seeds by which the mushroom reproduces. To the human eye a thimble full of spores / spawn would resemble a fine powder. In nature many of these fungal spores are dispersed by a number of modes, wind water and so forth away from the parent mushroom, where they are more apt to find suitable conditions under which to survive and reproduce. Only a very small percentage randomly land at a suitable location where they can remain viable, survive and develop into new mushrooms.
Mushroom cultivation requires that we provide a suitable environment for our spores to develop into mycellium which in turn produces mushrooms. If we were to rely solely on the random process as nature does, mushroom cultivation would simply not be economically viable.
The most common method of growing mushrooms is from spawn / spores. However another method which is just as viable is to bypass the spores and go straight to the mycellium from which the mushrooms sprout. This can be done by using the mushroom stems.
Separate the stems from the umbrella like tops.
The stems or ends contain the mycellium, which is a fuzzy light colored material, tiny threads that somewhat resembles spider webbing. Dice the ends into 1/4 inch pieces. Next you'll need a growing medium or bedding and a container. The container can be any container capable of hosting the bedding, such as a cardboard box, bags like the leaf bags home depot sells or even a plastic storage bin.
Suitable Medium and Containers
Suitable medium can be straw, sawdust, compost or manure, coconut fiber, spent coffee grinds and so forth. Different mushrooms fare better or worse as the case may be on different mediums so it is advisable you research what bedding / medium is best for your particular crop and circumstances.
You want to layer your medium within the container. Place slightly moistened medium on the bottom followed by the diced chunks of mushroom stems and then another thin layer of stems and more medium. Keep the the medium and mycelium persistently damp, but not saturated and in the dark location. Misting of the medium , not watering as you would plants is the best way to maintain a moist environment.
If your container has a lid you'll need to poke some holes in the top for air flow. If you used a container without a lid, such as a cardboard box or leaf bag you'll need to cover the top with plastic wrap or garbage bags with holes poked in them - for air flow. Optimal temperature range is 65 to 75 degrees Fahrenheit.
You shouldn't see any observable activity for about 3 weeks, sometimes a tad longer before you see the mycellium devloping. Once the mycellium forms it will be roughly 2 to 2.5 weeks before you have harvestable mushrooms