Mushroom Growth: From Spores To Fruiting

Mushrooms are fungi, which require different conditions to grow than plants. They grow from the tip of the hypha, a sort of bud that extends forward in response to external stimuli. The dominant theory is that an organelle called the Spitzenkorper organises and directs the growth patterns in pulses. The hyphae then quickly begin branching, forming a dendritic network known as mycelium. The mycelium grows, gathering nutrients and water from its surroundings. When it encounters another compatible mycelium, it fuses and swaps nuclei, forming a dikaryotic mycelium. This secondary mycelium continues to grow until it runs out of food or space, or there is another signal like heavy rainfall or a temperature change to start fruiting. The mycelium then condenses into the smallest stage of mushrooms, known as primordia.

Mushrooms are fungi, not plants

Fungi have their own unique set of health benefits that are not found in plants or animals. Mushrooms are the fruiting body of fungi, akin to an apple that spreads spores, similar to how fruits spread seeds. The fungus's mycelium grows underground, like the roots of a plant, and the mushroom fruits above the ground. The mycelium grows into and around the food source, secretes enzymes for external digestion, and then absorbs the already-digested nutrients.

The process of growing mushrooms is also different from that of plants. Mushrooms are grown in a highly controlled environment, and the substrate provides a nutritional balance of organic material to serve as a growth medium. Mushroom spawn, purchased from commercial labs, is mixed with the substrate and transferred to trays or beds. The pinning stage occurs when "pins" of mushrooms push up through the casing, and the mushrooms are then harvested by hand.

The classification of mushrooms as fungi, rather than plants, has important implications for how we understand, support, and engage with them. This classification also affects the methods and equipment used for commercial mushroom growth.

The growth process

Mushrooms are fungi and require different conditions to grow than plants. The growth process for mushrooms is unique and fascinating.

To begin, a grower prepares the basic growing medium, called a substrate. This is a mixture of decayed organic matter, such as synthetic compost or manure-based compost, that serves as a nutritional balance of organic material for the mushrooms to grow in. Mushroom spawn, which can be purchased from commercial labs, is then mixed with the substrate. The spawn is the living tissue of the mushroom, from which single-celled hyphae are sent out. The hyphae quickly begin branching, forming a dendritic network known as mycelium, which is the white cobweb-like substance seen in spawn bags. The mycelium grows, gathering nutrients and water from its environment. When it encounters another compatible mycelium, the two fuse and swap nuclei, forming a dikaryotic mycelium. This secondary mycelium continues to grow until it runs out of food or space, or there is a signal, such as heavy rainfall or a change in temperature, to start fruiting. The mycelium then condenses into the earliest stage of mushrooms, called primordia. With the right conditions, the primordia become fully formed mushrooms, and the cycle begins again.

In a commercial setting, the mushroom spawn mixture is transferred to several hundred beds or trays. These trays are then covered with a casing made of peat moss, which helps to hold in moisture. During the pinning stage, "pins" of mushrooms push up through the casing and are harvested by hand throughout a 16-35 day cycle. After harvesting, the trays are emptied and pasteurized with steam before a new crop is started.

Mushrooms can also be grown at home in a garden or on logs. To grow mushrooms from mushrooms, one must use freshly bought organic mushrooms. The stems are sliced and layered into moist straw, kept dark and moist. Mushrooms may start to form after a few weeks and should be harvested daily once they are large enough to eat. Some types, like button mushrooms, should be harvested with a sharp knife to cut the stem cleanly at the base, encouraging regrowth. When growing mushrooms on logs, hardwood logs such as oak or beech are implanted with dowels no more than six weeks after being cut.

The role of spores

Mushrooms are fungi, and their growth process is unique and fascinating. The role of spores in mushroom growth is critical. Spores are the units of sexual or asexual reproduction in fungi. They are tiny cells that form on special hyphae and are so small that more than 1,000 would fit easily on a pinhead. Spores are adapted for dispersal and survival and can remain dormant for extended periods, even in harsh conditions.

Mushrooms produce billions of spores, which are responsible for the formation of new generations of fungi. The spores are released from the gills on the underside of the mushroom cap. The curved shape of the cap ensures that rainwater runs off, keeping the spores dry. When spores are released, they travel via wind currents and germinate when they land in a moist environment with an adequate food source.

Each spore that lands in a suitable location grows a network of fine threads called hyphae. These hyphae branch out in all directions, forming a colony. The hyphae release chemicals that break down the food, and the resulting nutrients are absorbed by the growing fungus. Over time, the threads of hyphae grow into a tangled mat, eventually forming a mushroom.

The spores of some mushrooms are spread by water droplets or with the help of animals like flies. For example, stinkhorn fungi have developed their spores in a foul-smelling slime that attracts flies. The flies consume the slime and carry the spores, depositing them later in their faeces.

Preparing the growing medium

Selecting the Substrate Materials

The choice of substrate materials depends on the type of mushrooms you want to grow. Generally, there are two types of starting materials for mushroom substrate: synthetic compost or manure-based compost. Synthetic compost can include wheat or rye straw, hay, crushed corn cobs, cottonseed meal, cocoa shells, and gypsum. On the other hand, manure-based compost is made from stable bedding from horse stables or poultry litter.

Mixing the Substrate

Once you've gathered the necessary materials, it's time to mix them together. The process involves converting plant and animal products into a mixture of decayed organic matter. Make sure to blend the right ingredients in the correct proportions to create a quality substrate. The substrate provides the necessary nutritional balance for mushroom growth.

Sterilization and Pasteurization

Before introducing the mushroom spawn, it is crucial to sterilize the substrate to prevent any unwanted contaminants from affecting the growth of your mushrooms. This can be done through various methods, such as steam sterilization or chemical treatments. Additionally, ensure that all equipment and tools are sterile to maintain a sterile environment throughout the process.

Inoculating the Substrate

Obtain mushroom spawn, which can be purchased from commercial labs. The spawn is the living tissue of the mushroom, and it will initiate the growth process. Mix the mushroom spawn with the substrate thoroughly. This mixture can then be transferred to trays or beds, depending on your setup.

Casing Application

Spread a layer of casing over the prepared beds or trays. The casing is typically made of peat moss and serves as a reservoir to hold moisture. This step helps create an optimal environment for mushroom growth and development.

Maintaining Moisture

Mushrooms thrive in moist conditions. Ensure that the growing medium is adequately watered or misted regularly. This can be done using a hose with a spray attachment, a watering can with a fine rose, or a hand mister. Maintaining moisture is crucial for encouraging mushroom growth and preventing the substrate from drying out.

By following these steps, you will successfully prepare the growing medium for mushroom cultivation. Remember that each step requires attention to detail and specific conditions to create an optimal environment for mushroom growth.

Harvesting mushrooms

Timing is Crucial:

When harvesting mushrooms, timing is of the essence. The goal is to harvest them when they are mature enough to have distributed most of their spores, ensuring the species' prosperity. However, if left too long, the mushrooms may stop growing, dry out, or release excessive spores, affecting their texture and flavour.

Signs of Maturity:

For most mushrooms, the key sign of maturity is the transformation of their caps. Generally, you should look for the caps to turn from convex to concave or flatten out. The gills under the cap will also enlarge and begin to drop spores. For oyster mushrooms, in particular, the ideal harvest time is when the edges of the caps start to uncurl and flatten, but before they become too flat.

Harvesting Techniques:

When it comes to harvesting, you can either pluck the mushrooms by hand or cut them. Some believe that cutting is preferable as it minimises disturbance to the surrounding area. However, a 35-year study from Germany suggests that the method of harvesting does not significantly impact the fungi, and environmental factors like weather carry more weight. Therefore, it is more important to focus on timing and maturity than the harvesting technique.

Wild Mushroom Harvesting:

Harvesting wild mushrooms requires extra caution. It is crucial to correctly identify the mushroom species, as many wild mushrooms are poisonous and can be fatal if consumed. Always wear proper clothing and boots when foraging for wild mushrooms, and follow guidelines for minimum cap diameters to ensure sustainability.

Magic Mushrooms:

Harvesting magic mushrooms requires careful attention to timing. Observe the veil, a thin membrane on the underside of the cap, which keeps the spores in the mushroom. Harvest just before the veil tears, as this will maximise future flushes and the potency of the mushrooms.

Frequently asked questions