Mushrooms are the reproductive structures of fungi, an entirely different biological kingdom from plants. Unlike plants, fungi are heterotrophs, meaning they must absorb nutrients from their environment rather than using photosynthesis. This fundamental difference dictates that while water is indispensable for their life cycle, simply placing a mushroom in plain water will not result in a new harvest. However, water plays a direct, yet temporary, role in specific cultivation techniques used to propagate the fungal organism.
Clarifying the Role of Water in Fungi Cultivation
Water is necessary for all stages of a fungus’s life, but its function changes depending on the phase. The vegetative body of the fungus is the mycelium, a vast network of thread-like cells called hyphae that colonize a food source. This mycelial network absorbs nutrients and must be established before the fruiting body—the mushroom we eat—can form.
To fruit, the mycelium requires a dense, nutrient-rich substrate like sawdust, grain, or compost, which provides the necessary moisture. Plain water lacks the complex carbohydrates, proteins, and minerals required to fuel the energy-intensive process of creating a physical mushroom structure. Water in cultivation is primarily used for hydration, maintaining humidity during the fruiting phase, and as the solvent base for initial microbial growth.
Growing Mycelium in Liquid Culture
The most direct way to grow fungus in water is by creating a Liquid Culture (LC), a sterile, nutrient-rich broth used to rapidly expand mycelium. This method creates an active, injectable solution used to inoculate a larger substrate later. The liquid medium is water mixed with a small amount of simple sugar, such as light malt extract, dextrose, or honey. A common recipe uses 3 to 4 grams of sugar-based nutrient for every 100 milliliters of water. The solution must be sterilized to eliminate competing microorganisms, typically by placing sealed jars into a pressure cooker at 15 pounds per square inch (psi) for 20 to 45 minutes.
After cooling, the sterile liquid is inoculated with pure mycelium tissue or a spore suspension. The mycelium rapidly colonizes the liquid, forming a fluffy, white mass suspended in the broth. The resulting liquid culture is a ready-to-use inoculum that dramatically speeds up the colonization of grain or sawdust substrate. To use it, a sterile syringe draws up the liquid and injects it into the final growing medium.
Propagating Mushrooms from Stems
Another common method involving water is propagating or “cloning” a store-bought mushroom from its stem. This technique is often what beginners envision when attempting to grow mushrooms in water, as it leverages the robust nature of the fungus’s tissue. To begin, the base of a fresh, healthy mushroom stem, particularly from species like Oyster or Lion’s Mane, is separated and placed into a container with water. The goal is not to fruit the mushroom in the water, but to encourage the vegetative mycelial network to grow outward from the stem tissue.
Within a week or two, a fine, fuzzy white growth of mycelium becomes visible around the base of the stem. This newly grown mycelium cannot be left indefinitely in the water, as it will exhaust the minimal available nutrients and will not produce a mushroom. The next step is to transfer the colonized stem butt and its mycelial growth to a solid, pasteurized substrate like coffee grounds, cardboard, or wood chips.
Necessary Environmental Controls for Water-Based Methods
Success in water-based cultivation hinges on maintaining stringent environmental controls, especially concerning sterility and gas exchange. Contamination, often from airborne bacteria or mold spores, is the single greatest cause of failure when working with nutrient-rich water solutions. For liquid culture preparation, every component, including the water, nutrients, and the container, must be sterilized using high-heat and pressure to eliminate competing organisms.
Once inoculated, the mycelium requires a steady temperature, typically ranging from 70 to 80 degrees Fahrenheit, for optimal growth. The fungal organism is aerobic, meaning it requires oxygen to thrive, which necessitates a system for gas exchange, such as a filtered lid on the jar. Regular, gentle agitation or shaking of the liquid culture jar is also necessary to break up large mycelial clumps and ensure the fungus has access to all the nutrients and oxygen throughout the solution.