Choose a substrate of leaf litter that is partially composted mixed with pine needles, soaked straw scattered over dirt, or an 80/20 mix of horse manure and straw seasoned with gypsum fertilizer for the proper pH. The substrate is the growing medium for the mushrooms. Fungus prefers partially decomposed matter, like compost. Mix your compost with the above combinations in order to tailor it to your blewits.
Choose a day from February through October to incorporate the spawn (this can be purchased online through reputable mushroom suppliers) into your chosen substrate. Rake back the leaf litter or straw until you reach bare soil, place the spawn, and cover back over with the substrate. The amount of spawn depends on how much compost you have; the general guideline is to use approximately 30 pounds of spawn to 1 ton of compost.
Add a casing layer on top. This may consist of peat or loamy soil. It should function to hold moisture and support the growing spawn but not be heavy enough to slow their growth. The casing layer should be about an inch thick or less.