Mushroom growing is a unique type of gardening. Mushrooms are really the fruit of a fungus that is grown from spores, or "mycelium," a mat of developing spores. Mycelium is also called mushroom "spawn." Ordinary soil does not provide the right kind of nutrients for growing mushrooms. Instead, other materials such as straw, sawdust, wood chips and compost are used as growing medium, called a "substrate." Different types of mushrooms require different kinds of substrate.
According to the University of California at Davis, wood chips can be used as the soil medium for those mushrooms that grow well on wood substrates. Mushrooms that grow in woody materials include oyster, shiitake, reishi, maitake and lion's mane mushrooms. You can purchase pre-sterilized wood chips ready for culturing the mushroom spawn.
Compost is a substrate that requires the most time to prepare, but it makes an effective soil-substitute for growing mushrooms. Compost is a mixture of yard waste, like leaves, grass clippings, weeds and branches, with kitchen waste like coffee grounds, vegetable scraps, eggshells and shells. This matter is kept moist and warm until it deteriorates into a rich, loamy soil-like material. You can make your own compost in a small enclosure in your yard in two to four months, according to the Pennsylvania Department of Environmental Protection. White button mushrooms prefer compost as substrate.
Straw can also be use as the substrate soil-substitute for growing mushrooms. According to Shroomery, cut wheat or barley straw into 2 to 4 inch pieces and pasteurized by putting it into 150-degree F water for 1 hour, then removed and allowed to drain. It is then cooled to room temperature. It is then placed in a bag with the mushroom mycelium, punctured several times and allowed to grow. Once the mycelium spreads on the surface, the bag is opened and the mushrooms are exposed to the air.
Horse manure grows mushrooms easily if composted well and mixed with straw. You can then place the mushroom spawn on the surface of the manure compost and rub it into the surface. A bit of lime will help the mushrooms grow. Do not water the manure compost for four weeks, as there is sufficient moisture in the compost, according to CountryFarm Lifestyle. You can purchase sterilized and composted horse manure for your mushroom substrate.
You can also use ordinary potting soil to grow mushrooms, but you must add additional organic material for the mushroom spawn to eat. Coffee beans, cut in half and soaked in water for five minutes, then placed on the soil gives the potting soil more structure and nutrients for growing mushrooms. Adding vermiculite will give the soil additional body to hold the spawn.