Edible mushroom production is a promising horticultural enterprise in Kenya, offering opportunities for income generation and improved food security. Preparing propagation materials and establishing an appropriate production environment are crucial first steps that determine the success of mushroom farming. This chapter focuses on how to select suitable sites for mushroom propagation materials and the construction of mushroom houses tailored to Kenyan conditions. Proper understanding and execution of these processes help optimize yields and maintain quality in commercial mushroom farming.

1.1 Siting mushroom production structure

Selecting an appropriate site for mushroom propagation materials and production structures is fundamental for ensuring optimal growth conditions and minimising contamination risks. In Kenya, where climatic conditions vary widely, site selection must consider factors such as temperature, humidity, and accessibility to water and raw materials. This section explores the definition of edible mushrooms, the tools and materials required for propagation, and essential considerations when siting mushroom production structures.

Environmental factors for siting

• Temperature control: Sites with stable temperatures between 20°C and 28°C reduce the need for artificial heating or cooling, lowering operational costs.
• Humidity levels: High relative humidity (80-90%) is necessary for mycelium growth and fruiting, so proximity to water sources or humid microclimates is advantageous.
• Shade and ventilation: Natural shade protects mushrooms from direct sunlight, which can dry substrates, while good ventilation prevents stagnant air and a build-up of carbon dioxide.
• Contamination risk: Avoiding areas near industrial pollution, rubbish heaps or heavy traffic reduces contamination from dust, moulds and chemical pollutants.
• Drainage: A well-drained, slightly raised site prevents standing water around the structure, which would encourage moulds, flies and rodents.

Practical considerations for siting

• Accessibility: Easy access to markets, raw materials (for example sawdust from timber yards) and labour improves operational efficiency.
• Water availability: A reliable supply of clean water is essential for maintaining substrate moisture and environmental humidity.
• Space for expansion: Allowing room for scaling up production ensures sustainability and growth of the enterprise.
• Security and infrastructure: Sites within secure compounds with access to electricity facilitate stable operations and protect investments.
• Separation of work areas: Space is needed to keep the substrate preparation area apart from the spawning and incubation rooms, so that dirty and clean work do not mix.

Example of a well-sited unit

A group of oyster mushroom growers chose a site near a sawmill with abundant sawdust and access to water from a nearby river. The shaded location under large indigenous trees provided a natural microclimate suited to oyster mushroom cultivation, reducing energy costs for humidity and temperature control.

1.1.1 Definition of edible mushrooms

Edible mushrooms are fungi species cultivated or harvested for human consumption due to their nutritional value, flavour, and medicinal properties. They differ from wild mushrooms, which may be toxic, as edible varieties are selected for safety and palatability. The cultivation of edible mushrooms in Kenya focuses on species such as oyster mushrooms (Pleurotus spp.), button mushrooms (Agaricus bisporus), and shiitake (Lentinula edodes).

Characteristics of edible mushrooms

• Nutritional value: Edible mushrooms are rich in proteins, vitamins (especially B-complex), minerals like potassium and selenium, and dietary fibre, making them an important food source in nutrition programmes.
• Growth requirements: They require specific substrates such as sawdust, coffee husks, or maize stalks, which serve as a nutrient base for mycelium growth under controlled humidity and temperature.
• Non-toxicity: Unlike many wild fungi, edible mushrooms have been tested and deemed safe for consumption, reducing the risk of poisoning.
• Reproductive method: They reproduce through spores, which germinate to form mycelium, the vegetative part that colonises substrates.
• Economic importance: Edible mushrooms contribute to income diversification for smallholder farmers and commercial enterprises, supporting the horticultural sector.

1.1.2 Tools, equipment and materials used

Successful mushroom propagation depends on the availability and proper use of specific tools, equipment, and materials. These facilitate substrate preparation, supplementing, packing, spawning, incubation, and fruiting. The table summarises the items used, and the sections that follow explain how the six main items are used in the spawn preparation workshop.

• Autoclaves or pressure cookers are essential for sterilising small batches of substrate, preventing contamination by unwanted fungi or bacteria.
• Selecting appropriate substrate materials is critical, as the nutrient content and physical properties influence mushroom yield and quality.
• Monitoring equipment ensures that the mushroom house environment remains within the ideal temperature (20-28°C) and humidity (80-90%) ranges for propagation.
• All tools that touch the substrate or spawn must be clean and wiped with a disinfectant before work begins.
• Materials such as substrate and supplements must be stored dry and off the floor to prevent moulds from developing before use.

1.1.2.1 Weighing scale

A weighing scale is used to measure the quantity of substrate, supplement and spawn that goes into each batch. Accurate weighing keeps the recipe the same from batch to batch, so that results can be compared and problems traced. For example, a grower preparing 20 kg of dry sawdust weighs the sawdust and the supplement separately before mixing.

• Place the scale on a firm, level surface so that readings are steady.
• Check that the scale reads zero before each weighing.
• Use a clean container and set the scale to zero with the container on it, so that only the material is weighed.
• Do not exceed the stated capacity of the scale.
• Wipe the scale after use to remove dust and substrate residues.

1.1.2.2 Poly tubes

Poly tubes are lengths of heat-resistant plastic tubing that are cut to size and filled with moist substrate to make growing bags. Heat-resistant polypropylene is preferred because the substrate is pasteurised or sterilised with heat, and ordinary thin polythene can soften or melt. A tube is closed at one end, filled with substrate and spawn, then closed at the other end to form a bag for incubation.

• Cut tubes to equal lengths so that bags hold similar amounts of substrate.
• Check each tube for holes or tears before filling, because they let in contaminants.
• Fill firmly, without overfilling, so that the tied end stays secure.
• Make small holes or slits only where the production method requires them for fruiting.
• Keep unused tubes clean and dry in a closed store.

1.1.2.3 Lockable drum

A lockable drum is a clean metal drum with a tight-fitting lid that can be locked. It is used to pasteurise substrate with steam or hot water, and to store materials such as soya bean meal or spawn away from rodents, insects and theft. A drum with a tight lid holds heat and steam around the substrate, which helps to kill competing organisms before spawning.

• Use a drum that is free from rust and from previous chemical or oil contents.
• Keep the substrate above the water level so that it is pasteurised by steam and does not soak.
• Close and lock the lid during pasteurising so that heat is retained.
• Let the substrate cool before spawning, so that heat does not kill the spawn.
• Wash and dry the drum after every batch to prevent mould build-up.

1.1.2.4 Table spoon

A table spoon is a stainless steel spoon used to measure small quantities of supplement and to transfer spawn into the substrate. It is cheap but must be kept clean, because a dirty spoon can introduce contaminants directly into the spawn. For example, one spoon is kept for soya bean meal measuring and a separate, disinfected one for spawn handling.

• Wash the spoon with clean water and soap, then rinse well.
• Wipe it with a disinfectant such as alcohol before handling spawn.
• Use separate spoons for supplement and for spawn.
• Level the spoon each time when measuring so that quantities are consistent.
• Keep the spoon in a clean covered container between uses.

1.1.2.5 Sisal twines

Sisal twine is a strong natural fibre string used to tie the open ends of filled poly tubes and to hang the bags in the mushroom house. A secure tie keeps contaminants out and holds the substrate and spawn in contact. Sisal is strong, cheap, and does not melt when used near warm substrate.

• Tie the bag end tightly just above the substrate, leaving no gaps.
• Use a double knot so that the tie does not slip during handling.
• Cut the twine in equal lengths before the day's work begins.
• Keep twine dry and clean, since damp twine may carry moulds.
• When hanging bags, check that the twine is strong enough for the weight of the bag.

1.1.2.6 Supplement (soya bean meal)

Soya bean meal is a protein-rich supplement mixed into the substrate to feed the mycelium and raise yields. Substrates such as sawdust and straw are low in nitrogen, so adding a small proportion of soya bean meal speeds up mycelium growth. Too much supplement can encourage moulds and cause heating, so the amount must be weighed and mixed evenly.

For example, if the supplement is added at 5% of the dry substrate weight for 20 kg of dry sawdust:

Formula: supplement mass = dry substrate mass × rate ÷ 100

Substitution: supplement mass = 20 kg × 5 ÷ 100

Working: 20 × 5 = 100, and 100 ÷ 100 = 1

Result: supplement mass = 1 kg

• Use fresh meal that is dry, free-flowing and has no musty smell.
• Weigh the supplement on the scale rather than estimating.
• Mix it thoroughly through the substrate so that there are no pockets of concentrated meal.
• Store the meal in a closed, lockable container away from moisture and rodents.
• Discard any meal that is damp or mouldy.

Chapter Summary

This chapter focused on preparing propagation materials for edible mushroom production, beginning with the definition of edible mushrooms and identifying essential tools and equipment such as weighing scales, poly tubes, lockable drums, tablespoons, sisal twines, and supplements like soya bean meal. It then covered the construction of a suitable mushroom house, emphasizing the importance of an environment conducive to mushroom growth. The treatment of starter culture was explored, detailing the use of organic soils, plant growth regulators, vitamins, amino acids, and different propagation media including grain, liquid, and wood. The chapter also discussed the process of mushroom spawning, highlighting methods for inoculating the growing substrate. Practical steps for constructing a mushroom house were revisited to reinforce understanding. Finally, it described how to carry out treatment of the starter culture and perform spawning using various methods such as layering and broadcasting to ensure successful mushroom cultivation.