The discarded stem ends, often called “butts,” from store-bought mushrooms can be used to grow new fungi at home. This accessible cultivation method relies on cloning the existing living tissue within the stem. This method is fundamentally different from planting a seed or rooting a plant cutting, as it relies on cloning the existing living tissue within the stem.
Understanding Mycelial Growth
The mushroom harvested for food is only the reproductive structure, known as the fruiting body. The true organism is a vast, hidden network of microscopic fibers called mycelium. This vegetative network functions like the root system of a plant, spreading through a food source to absorb nutrients and water.
The mycelium is a dense, white, thread-like mass that collects energy until conditions are right to produce a new mushroom. The bottom of the stem, especially in varieties like oyster or button mushrooms, contains remnants of this living mycelial tissue. This tissue is the biological resource used for “regrowth,” encouraging the existing organism to colonize a new food source. This technique creates a clone of the parent organism, bypassing the need for spores and making the process faster for home enthusiasts.
Step-by-Step: Regrowing Store-Bought Mushroom Butts
To begin the cloning process, select healthy, firm mushrooms, with oyster mushrooms being particularly successful for beginners due to their vigorous growth. Carefully trim the bottom section of the stem, aiming for a piece about one-quarter to one-half inch long, where the mycelium is most concentrated. It is helpful to use a clean knife and container to minimize the introduction of competing molds or bacteria.
The initial substrate for this tissue transfer must be moist and clean. Shredded cardboard or used coffee grounds are excellent, readily available options that provide the necessary carbon-rich material. Pasteurizing the medium by soaking it in very hot water and allowing it to cool helps reduce competing contaminants. Once cooled and drained to a damp but not dripping consistency, layer the mushroom butt pieces into the prepared substrate inside a container.
The container requires a lid or plastic wrap to maintain high humidity, but it must also have small holes poked into it to allow for gas exchange. This initial environment should be kept away from direct light and drafts, ideally at a stable room temperature. Over the next few weeks, the existing mycelium will begin to branch out from the stem piece, colonizing the new substrate with its white, cottony network. Once the entire medium is covered in this growth, the mass is ready to be transferred to a larger fruiting environment.
Creating the Ideal Growing Environment
Successful development and eventual fruiting depend on consistently managing three environmental factors: the substrate, moisture, and temperature. For long-term growth, the colonized material requires a substantial food source, or substrate. Common materials include pasteurized straw, hardwood sawdust pellets, or a mixture of coco coir and vermiculite. The chosen substrate must remain consistently moist, but excess water should never pool at the bottom of the container, as this suffocates the growing mycelium.
High humidity is a major requirement for the formation of the actual mushroom, or the fruiting body. This is achieved by placing the container inside a humidity tent or misting the surface multiple times a day with a fine spray of water. The ideal temperature range for many common edible species, such as oyster mushrooms, is between 65 and 75 degrees Fahrenheit (18 to 24 degrees Celsius). While the mycelium grows best in the dark, initiating mushroom formation requires a sudden change, including a slight drop in temperature and exposure to indirect light, such as a windowsill that receives no direct sun.