Every year, Kenyan farmers lose a significant portion of their harvest to poor storage. Maize develops aflatoxin. Beans get weevils. Tomatoes rot within days. Potatoes sprout or go soft. These losses are not inevitable. They are the result of specific problems (Moisture, temperature, pests, and poor handling) that have practical, affordable solutions.

For farmers, reducing post-harvest losses is often more profitable than increasing production. Growing an extra bag of maize requires land, seed, fertiliser, and labour. Saving a bag that would otherwise spoil requires only better storage practices and sometimes simple, low-cost equipment. This article covers practical storage techniques for Kenya’s most common crops, focusing on methods that work at smallholder scale without expensive infrastructure.

The information here is for farmers growing maize, beans, potatoes, onions, tomatoes, and other perishables. It is also relevant for agribusiness investors who want to understand where value is lost in the supply chain and how to capture that value by reducing waste.

Understanding Why Post-Harvest Losses Happen

Before looking at solutions, it helps to understand the main causes of spoilage. Different crops face different risks, but most losses fall into four categories.

• Moisture is the biggest enemy of dried grains and pulses. Maize and beans stored before they are fully dry develop mould, including aflatoxin-producing fungi. Even properly dried crops can reabsorb moisture from humid air or from contact with damp floors and walls.
• Pests cause the second major category of loss. Insects including maize weevils, larger grain borers, and bean bruchids lay eggs on or inside grains. The larvae eat the kernel from within, reducing weight, nutritional value, and marketability. Rodents also consume and contaminate stored produce.
• Temperature and humidity affect both drying and storage. High temperatures speed up insect breeding cycles and mould growth. Humidity above 65 % allows many stored products to reabsorb moisture, triggering spoilage.
• Physical damage from poor handling—dropping bags, using dirty sacks, stacking improperly—creates entry points for pests and fungi. Broken grains and bruised fruits spoil much faster than intact ones.

The good news is that each of these causes can be addressed with simple, low-cost techniques.

Proper Drying Before Storage

Drying is the most important step for grains, pulses, and oilseeds. No storage method can save poorly dried produce.

For maize, the target moisture content is below 13.5 percent. Farmers can test moisture by biting a kernel. Properly dried maize cracks cleanly with a sharp snap. If the kernel squashes or feels soft, it needs more drying. Shelled maize dries faster than maize left on the cob, but cobs allow better air circulation if stacked properly.

For beans and other pulses, target moisture is below 15 percent. Dried beans should be hard enough that a fingernail cannot dent them easily. Beans that are still slightly soft will develop mould or support weevil breeding.

The best drying method is sun drying on clean tarpaulins, mats, or raised platforms. Avoid drying directly on bare ground, which introduces soil contaminants and moisture from the ground. Spread produce in thin layers, ideally no more than 5 centimetres deep. Turn regularly for even drying. Cover during rain or heavy dew. In humid coastal areas, drying may take several days longer than in drier inland regions.

For farmers without tarpaulins, raised drying racks made from local timber and mesh wire work well. The key is keeping produce off the ground and allowing air to circulate underneath.

Hermetic Storage for Grains and Pulses

Hermetic storage means sealing produce in airtight containers. This method kills existing insects by depleting oxygen and prevents new insects from entering. It also maintains moisture levels, preventing mould growth. Hermetic storage is one of the most effective low-cost technologies available to smallholders.

Hermetic bags, sold under brand names like GrainPro and AgroZ, are specially designed plastic bags with two or three layers. After filling, the bag is tied or heat-sealed. As the stored grain continues to respire, oxygen levels drop and carbon dioxide rises. Insects cannot survive in this environment. No pesticides are needed.

A 50-kilogramme hermetic bag costs between KSh 150 and KSh 300, depending on brand and quantity. This is more expensive than a traditional woven sack costing KSh 50 to KSh 80, but the hermetic bag can be reused for three to five seasons. Over time, the cost is lower than repeatedly losing grain to pests.

For farmers who cannot access hermetic bags, modified methods work well. Thick food-grade plastic liners placed inside woven sacks and tied tightly can create a similar effect, though they are less durable. Used plastic jerrycans with tight lids work for small quantities of beans or maize for household use.

The key requirement is that the produce must be properly dried before sealing. Hermetic storage preserves dry grain; it does not dry wet grain. Sealing damp maize will lead to fermentation and spoilage within days.

Traditional Storage Structures Improved

Many Kenyan farmers use traditional granaries made from timber, mud, or woven grass. These structures work reasonably well when maintained properly, but small improvements can significantly reduce losses.

Raising the granary off the ground on stones or wooden posts prevents moisture rising from the soil and blocks rodent access. Fitting metal rat guards—smooth metal bands around the support posts—prevents rodents from climbing. Sealing cracks and holes with mud or cement keeps out insects and mice.

Inside the granary, hanging bags from rafters rather than stacking them on the floor improves air circulation and reduces contact with rodents. For maize stored on cobs, the traditional method of hanging cobs in bunches from the roof allows excellent air movement.

Smoke from cooking fires inside the granary, where culturally acceptable, repels many insects. This traditional practice has real scientific basis. The compounds in wood smoke are mildly insecticidal and create an unfavourable environment for pests.

Storage for Root Crops: Potatoes, Sweet Potatoes, and Cassava

Root crops require different storage approaches than grains because they are living, respiring products. The goal is to slow down sprouting, shrivelling, and rotting.

For potatoes, the best low-cost storage is a dark, cool, well-ventilated room. Light causes potatoes to turn green and produce solanine, a toxic compound. Warm temperatures trigger sprouting. High humidity encourages rot. Spread potatoes in a single layer on racks or shelves, never in deep heaps. Remove any sprouting or rotting tubers weekly. Under good conditions, potatoes can store for two to three months.

Sweet potatoes are more perishable than Irish potatoes. They are sensitive to cold damage below 10°C. Store them in a warm, humid place (around 25°C to 30°C) with good air circulation. Curing sweet potatoes immediately after harvest by keeping them in warm, humid conditions for four to seven days heals minor cuts and extends storage life. Farmers can create a simple curing chamber by covering stacked crates with plastic sheeting in a warm shed.

Cassava roots spoil within three to five days after harvest unless processed or stored using specialised methods. For short-term storage, leaving cassava in the ground and harvesting only as needed is the best approach. For longer storage, cassava can be chipped and sun-dried or fermented in water.

Onion and Garlic Storage

Onions and garlic need to be cured before storage. Curing means drying the necks and outer skins until they are papery and the neck is completely closed. This takes two to three weeks in a well-ventilated, shaded area. Spread onions in a single layer on racks or hang them in bunches. Do not cure onions in direct sun, which causes sunburn and reduces storage life.

Once cured, store onions and garlic in a cool, dry, well-ventilated place. Ideal temperatures are 5°C to 25°C, but the more important factor is low humidity. High humidity causes sprouting and rooting. Store in mesh bags, slatted crates, or hanging strings that allow air circulation. Plastic bags trap moisture and cause rot. Under good conditions, cured onions store for three to six months.

Farmers should sort stored onions regularly and remove any that go soft or begin sprouting. One rotten onion can spread mould to neighbouring ones.

Simple Cold Storage for Fruits and Vegetables

For tomatoes, leafy greens, capsicums, and other perishable produce, cold is the most effective preservation method. Smallholder farmers without electricity can use evaporative cooling structures, commonly called zero-energy cool chambers or charcoal coolers.

A zero-energy cool chamber is a simple brick or wooden structure. The walls are double-layered, and the space between the layers is filled with clean river sand or charcoal dust. Water is poured into the top of this filling, and it drips down through the sand. As the water evaporates from the outer surface, it cools the inner chamber. With daily watering, the interior stays 10°C to 15°C cooler than outside temperatures.

These coolers can be built for KSh 5,000 to KSh 15,000 depending on size and materials. A medium-sized cooler stores 50 to 100 kilogrammes of vegetables, extending shelf life from two days to up to two weeks for tomatoes and leafy greens. Farmer groups can share a larger cooler.

For farmers without a cool chamber, simple methods help. Harvest in the cool early morning, not mid-day. Keep produce shaded during transport to market. Use clean, ventilated crates rather than plastic bags, which trap heat and moisture. For leafy greens, sprinkling clean water and keeping them in a cool, shaded place can extend life by one to two days.

Airtight Container Storage for Tomatoes and Chillies

Drying is another option for perishable produce, particularly for tomatoes and chillies that will be sold as dried products rather than fresh. Sun-dried tomatoes fetch good prices in urban markets and have a shelf life of many months when stored properly.

Slice tomatoes thinly and spread on clean drying racks. Cover with mesh to protect from insects and dust. Drying takes three to seven days depending on sun intensity and humidity. Once fully dry and brittle, store in airtight containers in a cool, dark place. Dried chillies store well whole or crushed.

The key is ensuring complete dryness before storage. Any remaining moisture will cause mould. Farmers should also be aware that drying reduces weight dramatically; five kilogrammes of fresh tomatoes yield approximately one kilogramme of dried product. The higher price per kilogramme must account for this weight loss.

Pest Control in Storage Without Dangerous Chemicals

Many Kenyan farmers use pesticides inside storage, including products not approved for use on stored produce. This practice is dangerous and unnecessary. Simple, low-toxicity methods work well.

Diatomaceous earth is a fine powder made from fossilised algae. When dusted on grains or beans, it scratches the outer waxy layer of insects, causing them to dehydrate and die. It is harmless to humans and animals. Food-grade diatomaceous earth costs KSh 300 to KSh 500 per kilogramme and treats one to two tonnes of grain. Mix thoroughly with the grain before storage.

Neem leaves have traditional use as a storage protectant. Dried neem leaves mixed with beans or maize repel many insects. The active compounds are volatile and dissipate over time, so leaves need replacement every two to three months. For small quantities, this is a free and effective method.

Cleanliness is the most important pest prevention strategy. Sweep and wash storage areas between uses. Remove all old grain, dust, and debris before adding new harvest. Cracks and crevices in walls and floors harbour insect eggs and larvae. Sealing these cracks with cement or mud removes hiding places.

Recognising and Managing Aflatoxin Risk

Aflatoxin is a poison produced by certain moulds that grow on maize, groundnuts, and other crops. It causes liver damage and is linked to cancer. High levels can cause immediate illness and death. Aflatoxin contamination is a serious problem in many parts of Kenya, particularly during drought years or when maize is stored damp.

The only way to prevent aflatoxin is to prevent the mould from growing. This means drying maize to below 13.5 percent moisture before storage and keeping it dry. Hermetic storage helps because the low oxygen environment suppresses mould growth even if moisture is slightly above ideal levels, but it is not a substitute for proper drying.

Farmers who suspect aflatoxin contamination should not consume or sell affected maize. Discoloured, musty-smelling, or visibly mouldy grain should be destroyed. Simple testing is not available at farm level, so prevention through proper drying and storage is the only practical approach.

Practical Takeaways for Kenyan Farmers

• Dry all grains and pulses thoroughly before storage. Test by biting or by feeling for hardness. Sun-dry on clean surfaces, not bare ground.
• Use hermetic bags for maize and beans to eliminate insect damage without pesticides. For farmers without hermetic bags, use thick plastic liners inside woven sacks and seal tightly.
• Raise traditional granaries off the ground, fit rat guards, and seal cracks.
• For potatoes and sweet potatoes, store in dark, cool, well-ventilated spaces and remove rotting tubers weekly.
• Build a zero-energy cool chamber for tomatoes and leafy greens.
• For onions and garlic, cure thoroughly before storing in dry, airy conditions.

Keep storage areas scrupulously clean between harvests. Never use unapproved pesticides inside stored produce.

Better Storage Means Better Income

Post-harvest losses are not a natural disaster. They are a solvable problem. The techniques described here require little cash investment, mostly labour, attention, and changed habits. For farmers who adopt them, the payoff is immediate: more food for the family, more produce to sell, and better prices from buyers who recognize quality.

Start with one or two changes this season. Dry maize more thoroughly. Buy a few hermetic bags for the best beans. Build a simple rack for potato storage. Each improvement reduces losses and increases income. Over time, good storage practices become routine, and the old pattern of losing a third of the harvest to spoilage becomes a memory.

Farmers seeking hermetic storage bags, diatomaceous earth, and expert guidance on post-harvest handling can contact Organic Farm for quality products and practical advice. Visit the website at www.organicfarm.co.ke, call or WhatsApp +254712075915, or send an email to oxfarmorganic@gmail.com.