Edible mushroom production is a growing horticultural enterprise in Kenya, offering opportunities for income diversification and enhanced food security. Successful mushroom cultivation begins with proper preparation of propagation materials and site selection, which determine the quality and yield of the crop. This chapter guides horticulture professionals through the essential steps of choosing an appropriate site, understanding edible mushrooms, selecting the right tools and materials, and constructing an effective mushroom house. These foundational practices are critical for farmers and agribusinesses aiming to establish sustainable mushroom production ventures.

1.1 Siting mushroom production structure

Selecting the right site for a mushroom production structure is a critical decision that influences the productivity and health of the crop. A mushroom house sited in a hot, dusty or poorly drained place will struggle to hold the humidity and cleanliness that mycelium and fruiting bodies need. This section covers where to place the structure, the definition and characteristics of edible mushrooms, and the tools, equipment and materials used to prepare propagation materials.

Criteria for siting mushroom production structures

Choosing the site involves balancing environmental, logistical and economic factors. A site that scores well on all three gives stable growing conditions and keeps running costs low.

Environmental considerations:

• Temperature range: The site should keep temperatures suitable for the species grown. Oyster mushrooms, for example, fruit well at about 18°C to 28°C, depending on the species, so a hot, exposed site without shade is unsuitable.
• Humidity levels: Natural humidity should be moderately high, or it must be controllable by misting or damp floors. Dry, windy sites lose moisture from the substrate quickly.
• Air circulation: Adequate ventilation prevents the build-up of carbon dioxide and reduces contamination risks. The site must not, however, expose the house to strong, dusty winds.
• Shade availability: Partial shade protects the house and substrate from direct sunlight, which dries the growing media and overheats the structure. Mushrooms do not need sunlight to grow.
• Water accessibility: A reliable source of clean water is needed for substrate preparation, cleaning and humidity maintenance.
• Drainage and surroundings: The ground should drain well so that the floor does not stay waterlogged. The site should be away from manure heaps, rubbish pits and livestock pens, which are sources of competing moulds and flies.

Logistical and economic considerations:

• Proximity to raw materials: Sites near sawmills, coffee-processing units or farms reduce the transport cost of substrates such as sawdust, coffee husks or straw.
• Accessibility: Easy access to a road helps the movement of inputs and of harvested mushrooms, which are perishable.
• Market proximity: Being close to urban centres, hotels and open-air markets allows timely sales and reduces post-harvest losses.
• Land security: Secure land tenure ensures long-term operation without disruption to a structure that has been invested in.
• Cost of land and utilities: Affordable land and the availability of electricity or alternative energy affect the sustainability of the enterprise.

1.1.1 Definition of edible mushrooms

Edible mushrooms are fungi cultivated or harvested for human consumption because of their nutritional and culinary value. Unlike plants, mushrooms lack chlorophyll and obtain nutrients by decomposing organic matter, which makes them unique in horticultural production. Edible species grown in Kenya include Pleurotus species (oyster mushrooms), Agaricus bisporus (button mushroom) and Lentinula edodes (shiitake). These mushrooms contribute to food security by providing high-protein, low-fat food for urban and rural households.

Characteristics of edible mushrooms

• Nutritional value: Edible mushrooms are rich in protein, vitamins (notably B-complex and D), minerals such as potassium and selenium, and dietary fibre, making them valuable in balanced diets.
• Growth substrate dependence: They require organic substrates such as sawdust, straw or coffee husks, which serve as their nutrient source during growth.
• Temperature sensitivity: Different species have different optimal temperature ranges. Oyster mushrooms, for example, fruit well at about 18°C to 28°C, depending on the species.
• Short growth cycle: Most cultivated edible mushrooms mature within a few weeks of the substrate being fully colonised, allowing rapid turnover and several crops a year.
• Non-photosynthetic organisms: Growth does not depend on sunlight but on humidity, temperature and substrate quality, which influences site selection and structure design.

1.1.2 Tools, equipment and materials used

Successful mushroom propagation requires specific tools and materials to prepare substrates, inoculate spawn and maintain growing conditions. Items must be chosen for durability, hygiene and cost-effectiveness, because anything that touches the substrate or spawn can carry contaminants. In a small mushroom unit, for example, a trainee weighs the substrate, mixes in the supplement, packs it into poly tubes and ties them with sisal twine, using the same basic kit for every batch.

Handling points for the kit

• Spawn must be sourced from a reputable supplier to ensure strain purity and a high success rate of colonisation.
• Substrate preparation tools should be cleaned regularly to prevent contamination.
• Sterilisation or pasteurisation is critical to suppress competing fungi and bacteria that reduce yield.
• Humidity control devices help maintain a relative humidity of about 80% to 90% during fruiting.
• All handling should be done in a clean area, using clean hands or gloves and sanitised tools.

1.1.2.1 Weighing scale

A weighing scale is used to measure materials accurately so that every batch is prepared to the same recipe. Without it, the amount of supplement or spawn added is a guess, and results vary from bag to bag. For example, a grower preparing a batch of dry sawdust weighs it on a platform scale before adding the supplement.

• Substrate: Weigh the dry substrate so that the water, supplement and spawn rates can be calculated from it.
• Supplement: Weigh soya bean meal on a small, sensitive scale, since a small error in a small quantity is a large error in percentage.
• Spawn: Weigh spawn per bag so that each bag receives the same quantity.
• Harvest: Weigh harvested mushrooms to record yield and to price them for sale.
• Care: Place the scale on a level surface, check that it reads zero before use, and wipe it clean after use.

1.1.2.2 Poly tubes

Poly tubes are lengths of polythene tubing in which prepared substrate is packed and in which the mycelium colonises it. They are cut to the required length, with one end tied or sealed, then filled, inoculated and closed. A tube cut to about 60 cm, for instance, can be packed in layers of substrate and spawn, and then hung or stacked in the mushroom house.

• Material: Use polythene suitable for heat if the filled tube will be steamed, because thin or ordinary film may melt or tear.
• Cleanliness: Use new or well-cleaned tubes, since dirty ones introduce competing moulds.
• Filling: Pack the substrate firmly and evenly, leaving no large air gaps and no sharp pieces that can puncture the film.
• Aeration: The tube must allow enough air exchange for mycelium development, so small holes or slits are made as the technique requires.
• Sealing: Close the open end with a tie to keep out contaminants and to hold moisture.

1.1.2.3 Lockable drum

A lockable drum is a metal drum with a tight lid that can be fastened. It serves as an improvised steamer for pasteurising substrate in places without a purpose-made steriliser, and as a secure container for storing materials. For example, water is placed in the bottom of the drum, the substrate rests on a raised, perforated platform above the water, the lid is locked and the drum is heated so that steam passes through the substrate.

• Steaming: The locked lid keeps steam inside, so the substrate heats evenly and the competing organisms are suppressed.
• Water level: Keep the water below the platform so that the substrate steams and does not boil in the water.
• Cooling: After steaming, let the substrate cool to ambient temperature before mixing with spawn, because heat kills the fungal culture.
• Storage: A lockable lid protects supplements and clean substrate from rodents, insects and moisture.
• Safety: Handle the hot drum with protective gloves and open the lid away from the face to avoid steam burns.

1.1.2.4 Table spoon

A table spoon is a small, stainless steel spoon that holds about 15 mL and is used to scoop and measure small quantities. It is useful where a scale is not needed or where spawn grains must be placed neatly between substrate layers. A grower may use it to place spawn into a poly tube, for instance, without touching it by hand.

• Material: Stainless steel can be washed and sanitised repeatedly without absorbing moisture.
• Spawn handling: Use it to scoop and spread spawn evenly, reducing hand contact and contamination.
• Supplement: Use it to add small quantities of supplement or other additives to the mix.
• Sanitising: Wash it and wipe it with a sanitiser, or pass it through a flame and cool it, before touching spawn.
• Consistency: Use the same spoon, filled to the same level, so that each bag receives a similar amount.

1.1.2.5 Sisal twines

Sisal twine is a strong natural-fibre string used to tie and hang the poly tubes. It closes the mouth of a filled tube and supports the tube from a rack or pole in the mushroom house. A tube tied at the top and hung from a pole, for example, keeps the substrate off the floor, where it could pick up moisture and contaminants.

• Tying: Tie the mouth of each tube tightly enough to keep out contaminants but without cutting the film.
• Hanging: Use strong twine, as a wet tube is heavy and can break a weak thread.
• Cleanliness: Keep the twine clean and dry before use, since dirty twine carries spores onto the tubes.
• Cost: Sisal is cheap and locally obtainable, and it is biodegradable.
• Storage: Store it in a dry place away from rodents, which chew fibre.

1.1.2.6 Supplement (soya bean meal)

Soya bean meal is a protein-rich supplement added to substrates such as sawdust or straw, which are low in nitrogen. It feeds the mycelium and can improve the speed of colonisation and the yield. It must be used at the correct rate, since too much supplement feeds competing moulds and bacteria and increases the risk of contamination.

• Purpose: It supplies protein and nitrogen that straw or sawdust lack.
• Quality: Use clean, dry, mould-free meal, because damp or stale meal introduces contaminants.
• Rate: Follow the recommended rate for the species and substrate, usually a small percentage of the dry substrate weight.
• Mixing: Mix it evenly through the substrate so that every part of the tube receives some.
• Storage: Keep it dry in a sealed container, for example in the lockable drum, away from pests.

Worked example of a supplement rate, assuming a recommended rate of 5% of the dry weight:

Supplement mass = dry substrate mass × rate

Supplement mass = 20 kg × 5%

Supplement mass = 20 kg × 5 ÷ 100 = 1 kg

The grower therefore weighs 1 kg of soya bean meal for a 20 kg batch of dry substrate.

Chapter Summary

This chapter covered the preparation of propagation materials essential for edible mushroom production, beginning with the definition of edible mushrooms and the key tools and equipment required, such as weighing scales, poly tubes, lockable drums, table spoons, sisal twines, and supplements like soya bean meal. It then detailed the construction of a suitable mushroom house, emphasizing the importance of proper design for successful cultivation. The treatment of starter culture was explored, highlighting the role of organic soils, plant growth regulators, vitamins, amino acids, and various propagation media including grain, liquid, and wood substrates. The chapter also explained the spawning process, describing how to initiate mushroom growth. Practical steps for constructing a mushroom house were revisited to reinforce structural requirements. Finally, the chapter outlined the procedures for treating starter cultures and carrying out spawning using different methods, specifically layering and broadcasting, to ensure effective mushroom propagation.