Indoor mushroom cultivation is a rewarding way to produce fresh fungi while controlling the entire growth environment. This process mimics the natural life cycle of a mushroom within a sheltered space. By maintaining precise conditions of temperature, humidity, and airflow, you can successfully cultivate a variety of species, from culinary favorites like Oyster mushrooms to medicinal varieties like Lion’s Mane.
Selecting Supplies and Substrates
Choosing the right mushroom species is the first step, as their specific needs dictate the supplies you purchase. Beginner-friendly varieties, such as Oyster mushrooms, colonize rapidly and fruit reliably on simpler substrates. More advanced growers may select species like Shiitake or Lion’s Mane, which often require richer, pasteurized hardwood sawdust blocks.
The initial mushroom culture can be sourced as spores, liquid culture, or pre-made grain spawn. Grain spawn, which is sterilized grain colonized with mycelium, offers the most reliable starting point for beginners. Spores are the cheapest option but carry the highest risk of contamination and require more technical skill.
The substrate serves as the nutrient source for the mycelium. Common choices include sawdust, straw, and coco coir mixed with vermiculite. Substrates must undergo preparation, either sterilization (to eliminate all competing organisms) or pasteurization (to reduce the microbial load).
You will also need equipment to monitor conditions. A grow chamber, such as a plastic tub or humidity tent, is necessary to contain the substrate. A combined thermometer and hygrometer allows you to track the temperature and relative humidity, which must be precisely controlled throughout the different growth phases.
The Incubation and Colonization Phase
The colonization phase begins immediately after inoculation, where grain spawn is introduced to the prepared substrate. Mix the spawn thoroughly throughout the substrate to ensure the mycelial network can expand. The inoculated substrate is then placed in the grow chamber for incubation.
During this period, the environment should be kept warm and stable, typically between 70°F and 80°F (21°C and 27°C). Mycelium thrives in this warmth, establishing its network without needing light. Keeping the environment dark helps maintain a consistent temperature and prevents premature fruiting.
The goal is for the mycelium—the white, thread-like vegetative body—to completely permeate the substrate block. This passive growth stage usually takes two to four weeks, depending on the species. Colonization is complete when the substrate turns solid white as the mycelial network fully encapsulates the material.
Contamination, often appearing as green, blue, or black mold, is most likely during incubation. Maintaining the correct temperature is important, as temperatures exceeding 84°F (29°C) can suppress mycelial growth while promoting contaminants. A fully colonized block is uniformly white and ready for the environmental “shock” that triggers the next stage.
Triggering the Fruiting Environment
Once the substrate is fully colonized, you must introduce environmental changes to signal the mycelium to produce a mushroom. This transition, known as the “fruiting trigger,” mimics natural weather patterns. The primary adjustments involve lowering the temperature, increasing humidity, and introducing fresh air.
The temperature should be reduced to a cooler range, typically between 60°F and 70°F (15°C and 21°C). This temperature drop initiates the formation of “pins”—the tiny, initial mushroom fruit bodies. Simultaneously, relative humidity must be dramatically increased and maintained, ideally between 85% and 95%.
High humidity is often achieved through regular misting of the chamber walls or by using a dedicated fruiting chamber. This humidity must be balanced with a significant increase in fresh air exchange (FAE). If CO2 concentration rises above 1,000 parts per million, the mushrooms will develop long, thin stems and small, malformed caps.
To manage FAE, introduce fresh air several times a day by fanning the chamber or using ventilation systems. Low-level ambient light is also necessary during this phase to provide directional cues for the developing pins. This light helps the mushrooms grow upwards, forming a natural shape.
Harvesting and Subsequent Flushes
The final stage is harvesting the mature mushrooms and preparing the substrate for subsequent growth cycles. Mushrooms are ready for harvest when their caps have nearly flattened and the veil is about to break or has just broken. Harvesting before the veil breaks prevents the release of spores, which can signal the mycelium to cease production.
The correct technique for harvesting is to gently twist and pull the mushroom from the substrate block, or cut the stem close to the surface. Ensure no significant remnants are left behind. Leaving tissue behind can create a breeding ground for mold and bacteria, compromising future growth. After the first harvest, the substrate is ready for the next round of production, known as a “flush.”
The mycelium will recover and prepare for a second, third, or even fourth flush, though the yield typically decreases with each harvest. To prepare the block for the next flush, you must rehydrate the substrate, as the first flush significantly depletes its moisture content. This is commonly done by soaking the entire block in clean water for several hours.
After rehydration, the block is returned to the fruiting environment, maintaining high humidity and fresh air exchange conditions. The next flush of pins will typically appear within two to three weeks. Repeat this process until the substrate shows signs of irreversible contamination or the flushes stop yielding a significant harvest.