Cashew nut is scientifically known as Anacardium occidentale, and locally known as Mkorosho, or Mkanju (Swahili). The crop originated from Northern part of South America. The Portuguese introduced cashew nut to Mozambique where it flourished forming extensive forests; eventually spread to the East African region.
In Africa, this crop has spread for over 500 years either naturally or through smallholder cultivation. In Kenya, cashew nut is grown along the coastal primarily in Kwale, Kilifi, Tana River and Lamu counties. Some production also takes place in Taita Taveta and Tharaka Nithi Counties.
Botany
The cashew nut tree (Fig. 1) is a fast growing tree that grows to a height of 10-12m tall. Its trunk is often irregularly shaped. The leaves are spirally arranged, leathery textured, elliptic to obovate, 4 to 22cm long and 2 to 15cm broad, with a smooth margin. The flowers are produced in a panicle or corymb up to 26cm long, each flower is small, pale green at first then turning reddish, with five slender, acute petals 7 to 15mm long.
The nut is attached to the lower portion of the cashew apple which is heart like or conically shaped. The cashew nut (seed) hangs at the bottom of the apple and is c-shaped or kidney shaped. The tree has an estimated economic life span of 45 years
Varieties and Yields of cashew nut in Kenya
Recommended varieties of cashew nut are A75/83, A100, A81 and A82. Cashew nut can either be propagated by seeds or grafted seedlings.
| Variety | Potential Yields /Kg/Tree | Kg/Acre |
| A81 | 50 | 1400 |
| A82 | 55 | 1540 |
| A75/83 | 70 | 1960 |
| A100 | 60 | 1680 |
Cashew nut propagation
Cashew nuts are usually propagated through seed or grafted seedlings
In propagation by direct seeding 3 seeds are planted in the planting hole and two months after germination the weak seedlings are uprooted leaving the strong one to grow. Propagation using grafted seedlings
Propagation through grafting starts by raising rootstock propagated from local cashew nut varieties. First step is visual selection of seeds to remove diseased or deformed seeds. The selected seeds are taken through flotation test in water. Seeds that sink are planted in pregermination beds.
Suitable Soils for cashew nut farming in Kenya
Cashew nut is widely regarded as a robust tree crop that can grow in any soil types, with little or no effect on productivity. While it is true that cashew has few soil requirements and can adapt itself to a wide range of soil conditions, its performance in terms of growth and yields is significantly improved by fertile soils of a suitable type.
The best soils for cashew are deep and well-drained sandy loams without a hard pan, which facilitate the quick development of the tap root and the lateral roots system. Deep sands, sandy loams, gravelly soils and red laterite soils have been shown to be ideal for cashew in a number of African countries. Cashew also grows well on pure sandy soils but this may lead to mineral deficiencies that require special nutritional attention.
Waterlogging and flooding often have a negative impact on cashew nutproduction. For this reason, heavy clay soils with poor drainage are not suitable for cashew cultivation.
According to the FAO (1994), the optimum pH of soil for cashew growth is between 4.5 and 6.5. A soil pH below 3.8 or above 8.0 will negatively affect cashew production. The cashew tree does not Tolerate saline soils well and tends to grow poorly in valleys, floodplains and swampy areas that have poor drainage.
In summary, red sandy loam, lateritic soils and coastal sands with a slightly acidic pH and good drainage are optimal for cashew nut production.
Climate
Cashew nut requires hot temperatures of between 24oC and 28oC but can thrive even in temperatures of 40oC. The optimum monthly temperature for cashew nut growing is 27oC.
Cashew flowering is not affected by day length. Trees normally flower towards the end of the rainy season, when new shoots emerge, and a dry spell during flowering and fruit setting ensures a better harvest and high quality cashew nuts. Heavy rainfall, evenly distributed throughout the year, is not favorable for cashew trees, though they will still grow and sometimes set fruits. An ideal climate for cashew has a well-defined dry season of at least four months to produce the best yields.
By contrast, the combination of excessive rainfall and high relative humidity during flowering may result in flower and fruit drop as well as an increased incidence of fungal diseases.
Planting and Land preparation
The land preparation for planting cashew trees is done in the same way as other annual crops, with ploughing and harrowing. A second harrowing may be necessary in areas with fertile soils and high rainfalls due to the growth of weeds. Alternatively, herbicides can be used to suppress weed growth before transplanting the cashew seedlings, which also facilitates the practice of intercropping.
Cashew nut should be planted at the beginning of the rain season. The best time for planting will depend on available soil moisture. In the Coastal lowlands, the best time for planting is between April to June.
To establish a cashew nut orchard, the following steps are recommended.
- Plough the land thoroughly, removing stems and roots
- Lay out the field by spacing holes 12m x 12m
A spacing of 6m by 6m can be adopted with intention of thinning to 12m by 12m at a later stage when the canopies start to overlap.
- Dig holes one or two months before planting. The depth should be 60cm x 60cm x 60cm (2ft x 2ft x 2ft)
- Mix the top soil with two buckets of well decomposed farmyard manure and 150g (7.5 table spoonful) of DAP
- Carefully remove potting bag without disturbing the roots and plant at the centre of the hole. Plant the cashew nut seedling at the same soil level as that of the soil when the seedling was in the potting bag i.e. avoid burying the graft union. Prepare a shallow basin and cover with mulch and water after planting.
- Water the plant every 3-4 days until it has properly taken
- Intercrop with short duration perennials e.g. papaya or food crops e.g. maize, cassava, cowpeas
- Vegetables e.g. tomatoes, melons, pumpkins, chilies, egg plants (brinjals)
- Ensure that the orchard is always free from all kinds of weeds
Recommended fertiliser rates
Animal and compost manure are the best fertilisers for cashew. However, if manure is not available and intensive production is carried out, chemical fertilisers, such as Diammonium Phosphate (DAP), Calcium Ammonium Nitrate (CAN) and Potassium Sulphate can be applied.
Fertilizer and manure rates for Cashew
| Year |
Fertilizer type and quantity/tree |
||||||
| Manure
(10 kg debe) |
DAP
(g) |
CAN (g) | Potassium Sulphate (g) | ||||
| Long rains | Short rains | Long rains | Short rains | Long rains | Short rains | ||
| I | 2 | 1 | 260 | 180 | 180 | 40 | 40 |
| II | 2 | 1 | 520 | 360 | 360 | 80 | 80 |
| III | 2 | 2 | 780 | 540 | 540 | 125 | 125 |
| Above III years | 2 | 2 | 780 | 540 | 540 | 125 | 125 |
Managing old cashew orchards
The following options are available for improving old cashew orchards depending on their condition.
Pruning
Pruning is done to remove unwanted plant parts.
Selective thinning
This is removal of unwanted trees from the orchard.
Pollarding
Pollarding is severe pruning of the tree at a height of about 3m to reduce canopy to allow easier spraying and harvesting.
Coppicing
Coppicing is cutting down the tree at a height of 1.5 m to 2 m to renew the canopy.
Top-working
Top working is grafting of sprouts from unproductive coppiced trees. Top-work 3-4 sprouts per stem.
Disease and pest management
The most notable pest that affects cashews is the cashew nut bug. Other insect pests include stem borers, thrips, mealybugs, weevils, caterpillars and leaf miners. Diseases that affect cashews include powdery mildew and anthracnose. The following are important pests and diseases of cashew found in the Coast.
| Diseases | Symptoms | Control/Treatment |
| Powdery mildew |
|
Spray with Bayfidan at a rate of 10-15 ml in 3 litres of water per tree per application. Start spaying at onset of flowering and apply 3 times at 14 days intervals. |
| Anthracnosis
|
|
Spray with any of the following:
Antracol Kocide DF Before & after flowering Remove diebacks before spraying |
| Pests | Symptoms | Control/Treatment |
| Cashew nut bug
|
|
Spray with Lebacid |
Harvesting and Post-harvest handling
Harvesting starts from November and extends to May. The peak is November-December.
Cashew nuts planted using seed begin bearing 3 to 4 years after transplanting the seedlings. The nuts should be harvested as soon as possible, especially under wet conditions and should be dried before storage.
Grafted seedlings begin bearing within 2 years of transplanting. Depending on age and maturity of plant, a tree yields between 10 to 100 kilograms of unshelled nuts per year. One hectare can thus produce between 2,000 to 5,000 kilograms of unshelled nuts per year. Although trees are production for 40 to 50 years, commercial harvesting is for 35 years.
The cashew nuts do not mature at the same time. The duration of harvest extends from 45-75 days and the nuts should be collected daily during this period. November to May is the harvesting period, with the peak harvest period from November to January.
To get good quality nuts, clear the area beneath the tree, collect fallen fruits, detach the nut from the apple and dry the nuts under the sun for about 2 hours. The nuts can be graded into Fair Average Quality (FAQ) and Under Grade (UG). FAQ are well matured nuts and they should be full and well dried (12% moisture content). The colour should be grey or pale brown. They should neither be wrinkled nor spotted
- Clear the area beneath the tree
- Collect fallen fruits
- Detach the nut from the apple
- Dry under the sun for about 2 hours
Grade into Fair Average Quality (whitish) and Under Grade (blackish).