Mushrooms are a type of fungi and, like many plants, can be grown as food in greenhouses. Unlike most plants, however, mushrooms do not require sunlight to grow. In fact, mushrooms grow best in cool, dark areas. If you have a space like this in your greenhouse, or if you are able to make a few modifications to create such an environment, you may be able to grow mushrooms yourself
Though a small amount of light will not hurt your mushrooms, they are best grown in darkness. To grow mushrooms in a greenhouse, you may need to make a few modifications to a portion of the greenhouse to block out light. You may also need to take steps to ensure that the temperature stays fairly stable, somewhere between 55 and 60 degrees Fahrenheit. Keep the air in the greenhouse moist, and take precautions against strong drafts which can be fatal to developing mushrooms.
Trays vs. Logs
Two of the most common ways to grow mushrooms are in trays or logs. Mushroom trays are typically at least 2 feet long and 10 to 12 inches deep, and they can be purchased prefabricated or built from scrap wood. Fill the trays with growing medium, then treat with mushroom spawn. If you plan to grow a relatively small quantity of mushrooms, you may choose to use a log instead. The log should be 4 to 6 inches in diameter, at least 40 inches long and cut from an oak or some other hardwood tree during the late winter or early spring. To use the log, drill several holes into the log and plug the holes with mushroom spawn.
Mushroom Growing Medium
While many edible plants and vegetables can grow in soil, mushrooms require a different kind of growing medium. Mushrooms grow best in organic materials that are rich in natural sugars as well as nitrogen. Horse manure mixed with straw makes an excellent growing medium for mushrooms because it is moist and nutrient-rich. It is also possible to make your own mushroom compost using corn fodder, straw, peat moss and water. Unless you plan to grow a large quantity of mushrooms, however, making your own growing medium may not be practical. Many people who grow mushrooms at home choose to purchase mushroom kits that include the growing medium and mushroom spawn.
Mushroom spawn comes in several forms, and the type you need may depend on the growing method you select. Two of the most common forms of mushroom spawn are bricks and flakes. When using flake spawn, mix it directly into the growing medium at a rate of 1 quart per 15 feet of growing space. Break brick spawn into golf ball-sized pieces and plant them 1 to 2 inches deep in the growing medium, spacing the pieces 6 inches apart. During the weeks after being planted, the spawn will begin to grow mycelium, the web-like root system used by mushrooms to retrieve nutrients from the growing medium.
Caring for Mushrooms
Several weeks after planting the mushroom spawn, the growing area should become covered in a white web of mycelium. To encourage growth during these weeks, raise the temperature in the greenhouse to between 65 and 70 degrees Fahrenheit. Watering is also important during this stage to keep the spawn moist - mist the trays or logs with water twice a day for the best results. Once the mycelium forms, drop the temperature back down to 60 degrees Fahrenheit and cover the trays or logs with a thin layer of garden soil or damp newspaper. After another few weeks, tiny mushroom heads should begin to appear.
You can pick mushrooms when they are still small, in the "button" stage, or when they grow to maturity. To harvest mushrooms, use a sharp knife to cut the stem at the base. You may also harvest the mushrooms by hand, pressing down the soil around the stem with one hand and gently twisting the mushroom to separate it from the compost. Once your first batch of mushrooms appears, new growths should appear every 10 to 12 days until the compost becomes exhausted of nutrients. After harvesting your mushrooms, mist the compost twice a day until new growths appear. Do not spray developing mushrooms with water because they will most likely turn brown and die.