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Introduction to mushroom growing

Introduction to mushroom growing

A mushroom is a macro fungus with a distinctive fruiting body. The fruiting body is large enough to be seen by the naked eye. Mushroom are heterotrophs.


Vegetative growth – involving linear growth of mycelia.
Reproductive growth.-under favourable conditions mycelial growth produce fruiting bodies.

1. Nutritional value.
2. Food
3. Income generation
4. Cleaning the environment by recycling farm wastes
5. Medicinal value


-wheat straw
-rice straw
-saw dust
-cotton seed hulls
-sugarcane burgesses
-bean straw
-Maize straw
N.B oyster mushroom grows on almost all substrates containing lignin and cellulose.


  1. Cost of substrate
    ii. Availability of substrate
    iii. Cleanliness (the substrate should be contamination free) eg. mould.
    iv. Yield
    v. Ease of use
    vi. Age of the substrate


  1. a) SHREDDING– cut the substrate into small pieces measuring 3-6cm, this is done for straw. When using saw dust it’s important to compost it first because it contains some poisons revered to as lignin phenols. It’s heaped to 1.8m high and watered regularly until it attains a watery state. 1% lime is added as a P.H buffer and 1% urea is also added to increase the nutrient content of the substrate.
    b) SOAKING-the substrate is soaked for about twelve hours. However some substrate needs no soaking.
    c) BRENDING–after soaking the substrate is left to loses water for 1hr. the moisture content of the substrate can be checked by squeezing. After draining the water the substrate is mixed with 20% bran and 2% lime as a PH buffer.
    d) BAGGING–polythene bags are used in bagging the substrate. 9 by 15inches and 10 by 15inches.
    e) STERILIZATION BY STEAMING—for sterilization a metallic drum is used. A wooden rack (platform) which is about 21cm is placed at the bottom of he drum. About 40litres of water is put in the drum.
    – the bags containing the substrate are the arranged in the drum on top of the platform. The bags are arranged in such a way that they will allow steam movement.
    -the bags are then steamed for 4-4 and a half hr. the flames should not be allowed on the side of the drum, this is because dry heat would burn the polythene bags.
    – Temperature should be maintained at around 95 degrees. The drum should have a hole or two to allow steam to escape.
    -too vigorous boiling wastes fuel without reading to any increase in temperature. It may also lead to evaporation of all the water and this would lead to the polythene bags containing the substrate getting burnt. After pasteurization the heat is turned off and the drum allowed to cool down for sometime before it is opened. The substrate is allowed to cool to 28 degrees. It should be left in a clean environment for 24hrs.
  2. f) SPAWNING-introduction of mushroom spawns in the bags of substrate.
    This requires a clean aseptic condition to prevent contamination of the substrate. A spawning chamber should be used for spawning, after the bags are ready for spawning.

    The rubber band tying the outer pp bag is removed before he bags are put in the spawning box. This is to make the spawning quicker. The cotton wool will provide the oxygen required for the growth of the mycelia. Without adequate aeration the mycelia will grow very slowly hence the removal of the rubber band.

    A number of bags (about 20) are put in the box. Spawn is first shaken to loosen it and the spawn bottle put in the box which is the closed. The inside of the chamber is then sprayed with 70% alcohol. Some farmers use methylated spirit to sterilize the inside of the chamber. The alcohol fumes kill the microbes in the chamber and now spawning can be done. Care should be taken because alcohol is flammable so naked flames or sparks can easily ignite the alcohol.

    The worker also sprays some alcohol on his hands. Spawning requires a careful hand and speed. The cotton plug is removed from the mouth of the bag and piece of spawns poured into the bag using the other hand. The cotton plug is then replaced as soon as the spawns are added. The plug should be tight enough to keep insects from entering the bag.

    A ¼ litre bottle is enough to spawn 25bags. One litre of spawn spawns 100bags. The bags should not be left open for long as this gives the contaminants enough time to enter the substrate.


The spawned bags are arranged on shelves in the growing house and left alone for about 4wks. During this time the white mycelia will be seen growing from the top to the bottom of the bag. The optimum temperature for the growth of mycelia is 25 degree. Light is not necessary for this stage of growth but some diffuse light does no harm. That’s why it is possible to do incubation in the same room used for fruiting. Some farmers however construct a dark room for incubation. In oyster mushroom production the provision of a dark room is optional.

Aeration will be provided by the cotton plug. Spraying with water is not necessary at this stage. Although when the temperatures are too high spraying can be done to cool the growing house. When the mycelia have grown to the bottom of the bags, his marks the end of incubation and the mycelia are ready for fruiting.

Insects should be checked and controlled for they spread infections. They may also lay their eggs on the cotton wool and the substrate. The bags should be checked for contamination and any bag sawing signs of contamination should be removed from the growing room to avoid spread of the infection. Such bags should be discarded far away from the growing house.


The four environmental conditions required for fruiting (light, temperature, relative humidity, and aeration) should be optimum for best results. The bags are opened by removing the PVC neck and cotton wool .this allows space for mushrooms (fruiting body) to grow as they cannot grow through the plastic. The bag is rolled back to expose the top of the substrate for fruiting.

As soon as the bags are opened spraying starts .the floor, wall and all surfaces are sprayed with water to raise the relative humidity to above 95%.the mycelia are also sprayed with a very fine mist of clean water from a distance of 2 feet. Bigger droplets disturb mycelia and could delay fruiting or even stop it completely. As soon as fine droplets start trickling down on the mycelia spraying should stop because too much water on the substrate attracts bacterial growth. Spraying is done 2-3 times in a day depending on the prevailing environmental conditions.

Spraying also lowers the temperatures which is necessary for fruiting of mushroom. For many species of mushrooms a cold shock triggers the fruiting. Aeration should be provided by opening the windows. Under poor aeration the mushrooms will have very long stems, small caps and most of them will abort. If the windows are too big then it will be hard to provide high relative humidity as the moisture will be blown away by wind.

After opening the bags tiny mushrooms will start growing from the surface of mycelia. They will first be visible as bumps then as pinheads which later grow to full sized mushrooms (first flush). The mushrooms are picked before the margins start rolling. Picking is done by holding the mushrooms from the base, pulling and twisting them to break them off the substrate. A knife should never be used never be used for harvesting as it leaves a stump which could later be attacked by bacteria leading to rotting of substrate.

After picking the scars are left to dry out for a day, it’s not recommended to spray directly on the scars immediately after harvesting. Under the above conditions (high relative humidity and light) the bags will produce another flush of mushrooms after five to seven days. Good strains will keep producing mushrooms up to eight flushes. Between the flushes it is sometimes necessary to scrap old mycelia on the surface to expose fresh mycelia (this activity encourages fruiting).

The last flushes are very weak though and now the bags can be removed from the growing house.
With good care a kilo of dry substrate can produce 1-2kg of fresh mushrooms.

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