The cashew tree (Anacardium occidentale) is a flowering evergreen. Despite its ornamental attraction it is primarily grown for its fruit, the nut and apple. This versatility makes it a popular choice for people when choosing fruit trees for their garden. Originating in Brazil, the plant has been grown in India since its introduction in the 16th century. Today it is cultivated in many areas of Africa and Asia.
The cashew tree is a popular addition to a garden for both its ornamental and fruiting qualities. They are best grown in warmer climates away from the danger of frost.
If you live in a warm climate and wish to add the cashew tree to your garden, this guide will take you through everything you need to know.
How To Grow A Cashew Tree
The cashew tree originates in warm, tropical areas. Doing best in areas where daytime temperature average around 77°F they are categorized in USDA zones 10-11.
Gardeners in cooler climates, where the temperature rarely drops below 50°F will also be able to grow the plants. However you will need to provide protection during cold snaps. Be warned, even with protection a deep freeze is likely to kill a cashew tree.
Selecting a Cashew Tree Seed
As long as the seed is fresh, germination is an easy process.
The distinctive fruit of the cashew tree. Here the kernel, housing the nut which doubles as the plants seed, emerges from the bright red apple.
The seed is simply the nut still inside the kernel. Seeds should be no more than 4 months old. Older seeds will fail to germinate. Seeds can be harvested straight from the plant. Allow them to dry in the sun for 3 or 4 days before sowing.
Seeds are best sown undercover, in a container. This allows you to give them a little extra protection as they grow.
How to Sow the Seed
You can sow seeds at any time.
Fill a large container with fresh compost. A handful of vermiculite can be mixed into the compost before planting. This helps to improve the drainage properties of the soil. The container should be clean and have drainage holes in the bottom.
Sow a couple of seeds at a depth of 5-10cm. Place the seeds at a slight angle in the soil, cover and water in. Sowing multiple seeds increases the chances of a healthy plant emerging. Weaker seedlings can be thinned out later on.
While seeds can be sown at any time, it is best to sow in the fall or winter. Saplings can then be grown on undercover until they are ready for planting out in the spring. This will give the saplings plenty of time in the ground before winter arrives.
Place the container in a light, warm location. Regularly check the soil to ensure it isn’t drying out. Don’t place the container in full sun. Too much heat can burn seedling leaves. It can also cause plants to fail.
Germination times vary. Some people will see results within a couple of days other people may need to wait 3 or 4 weeks.
Following germination keep the growing seedlings well watered. They should also receive plenty of light. Allow the seedlings to grow on in the container until you are ready to plant out.
A Grafted Cashew Tree
You may choose to bypass the growing from seed process by purchasing a grafted cashew tree. These are available from commercial growers as well as fruit nurseries.
Plants grown from seed will take up to 3 years to bear fruit. Grafted specimens will usually bear fruit within 18 months. Grafted plants also bear consistent fruit. This means that the fruit will bear the same characteristics of the parent plant. Like other fruit trees a cashew tree grown from seed will not always grow true to type.
Whichever method you choose, remember it will take 7 years before the tree is producing its optimum yield. A cashew tree can take up to three years to begin bearing fruit. Full maturity, and maximum yield production, won’t be realised until the plants are at least seven years old.
Planting Out a Cashew Tree
When the cashew tree begins to outgrow its container you will need to start hardening off the plant. This is an acclimatization period that helps tender, young plants adjust to their new environment.
The best time to harden off and plant out is in the spring. This allows the plant time to establish itself in its new location before winter.
Positioning your Cashew Tree
The cashew tree thrives in sandy or sandy-loam soil. A pH level of 5-6.5 is preferred. They will grow in most soil types as long as the location is well draining. The only soil type that should be avoided is heavy, clay soil. This can easily become waterlogged causing plants to develop root rot.
Digging the soil over before planting will help to break up large clumps of earth, weeds and stones that may stunt the root system. It also allows you the chance to enrich the soil by working in organic matter such as compost.
Your chosen location should be a south or west facing, frost free spot. It should also receive at least 6 hours of sunlight a day. Plants growing in shady locations may struggle to fruit. Finally there should be some shelter from strong winds.
How To Plant A Cashew Tree
Before planting rake or dig over the soil, breaking up large clumps of earth and removing any weeds or rocks.
Dig a hole that is large enough to comfortably hold the saplings root ball.
Carefully remove the sapling from the container. Try not to disturb or damage the root system. This can lead to the plant struggling to adapt to its new position or even failing.
If you are planting more than one tree, try to give it enough space to flourish. Remember the root system of a fully grown plant is far larger than its canopy.
Place the sapling in the hole. Fill the hole with soil and gently firm it down, being careful not to compact the soil.
This is now the time to place a stake or some form of support in the soil. Saplings require support to ensure that they grow straight and don’t topple over.
After planting water in well.
Cashews have a vigorous growth habit. Saplings will need to be spaced out to an all round gap of 10 meters or 30 feet.
Caring for a Cashew Tree
Once planted in its final position there are certain things you can do to help your cashew tree thrive.
Despite being fairly drought tolerant regular watering is required. Saplings and young plants in particular require more water than older plants. You will also need to water more often when the plants are in fruit.
Water young plants weekly. Not only will this help the plants to establish themselves, but it will double their rate of growth. Continue to water weekly until the plants are mature. In warmer climates you may need to water twice a week, if the soil around the base of the plant feels dry. Tap water or rainwater harvested from the garden can be used to keep plants hydrated.
Don’t over water the plants. This can cause soil to become waterlogged and roots to rot. It can also cause fruit to fall or rot.
Water plants regularly, especially when they are in flower. Incorporating a liquid plant feed into your watering routing will help to give plants the nourishment they require.
During wet periods and the winter months the plants will require less water. Water only if the soil feels dry. As the spring temperatures increase, gradually increase the amount of water you provide.
Fertilize plants regularly during the spring and summer months. This is particularly vital when the plants are in flower and fruit is forming. A fertilizer with a NPK 8-3-9 ratio will contain all the nutrients your cashew tree needs.
The dose you give will depend on the size of the plant and the growing conditions. Consult the packet for instructions on how to work out the correct amount.
While this may also vary, in general you will need to fertilize the cashew tree once every two months during the growing season.
Working in home made compost or manure around the base of mature plants will help to give it an extra nutrient boost.
Regularly weed around the base of the cashew tree. Weeds can take valuable moisture and nutrients away from the plant. Treat weed ridden soil with home made weed killer before planting your saplings.
Mulching as well as growing grass strips between lines of plants will discourage weed growth. It will also help to prevent soil erosion. Growing grass strips between plants discourages weed growth. Alternatively mulching around the base of a plant will have the same effect. It will also help the soil to retain valuable nutrients and moisture.
Adding mulch to the base of the plant will protect its root system from cold weather and mild frosts. It will also help the soil to conserve moisture, offer some protection from soil borne pests and discourage weed growth. Organic mulches, such as home made compost, will also add an extra nutrient boost to the soil. However synthetic mulches or stones and pebbles can also be used, and will offer some protection.
Pruning and Training a Cashew Tree
As the sapling establishes itself, during the first year, remove any sprouts that emerge from the base or roots of the plant. These sprouts can take valuable nutrients away from the cashew tree, stunting its growth.
Regularly prune away broken or diseased branches. This helps the plant to stay healthy. You will also need to remove branches that are becoming entangled or seem overcrowded.
Train young sapling branches by removing low or tangled branches. This will help the plant to take on a proper shape.
Damaged or diseased branches should be pruned away as soon as you notice them. Otherwise try to leave pruning until late summer or early fall.
Training young plants and branches will help the plants to maintain a healthy growth habit. There should be enough room between main branches for air to easily circulate. This will help to keep the plants healthy and discourage disease. It also gives the fruit more room to form.
Trees planted near south or west facing buildings or on south or west sloping inclines will enjoy some natural protection from frosts. Applying a 2-3 inch layer of mulch to the base of the cashew tree will also offer some protection. Organic mulches such as compost or manure will add nutritional value to the soil as they break down. Remember to regularly renew the layer during the winter months. This will provide continued protection to your plant.
Common Cashew Tree Problems
Healthy, well cared for plants will largely be pest and problem free. Occasionally the plants may come under attack from pests such as Blossom Webber, Stem Borer or Leaf Miners. Most pest infestations can be controlled with an application of fungicide. Stem grease will cure infestations of both Fruit and Nut Borer.
The most difficult pest infestation to deal with is the Western Flower Thrip. This has some resistance to pesticides. Consequently you may need to treat the cashew tree a number of times to fully get rid of an infestation.
If cared for correctly the cashew tree is a largely problem free plant. The major issue to watch out for is a zinc deficiency. Once identified, however, this is easily treated.
The cashew tree, particularly those growing in sandy soil, is prone to developing a zinc deficiency. If caught early enough this problem is easily treated. However zinc deficiency can be difficult to diagnose. Symptoms, such as leaf discoloration, can also indicate a deficiency of another nutrient. Unlike other deficiencies, zinc deficiency first becomes apparent on lower leaves, working its way up the plant. Other deficiencies tend to appear higher up on the plant, working their way down through the foliage. Ultimately the only way to confirm a zinc deficiency is to test the zinc levels in the soil. .
To boost the zinc levels in the soil, work in a quantity of chelated zinc. Home made compost or organic matter can also be regularly worked into the soil to help maintain zinc levels.
Spraying the leaves with micronutrient foliar zinc fertilizers or kelp extract will alleviate the symptoms. Don’t worry about overdosing the plant, the cashew tree will happily tolerate high levels of zinc.
Legumes, such as peanuts or beans, will provide ground cover, helping to enrich the soil. They can also help to maintain moisture levels and prevent soil erosion.
An attractive plant, that is popular with pollinators, borage is a good choice as a companion plant. Helping to prevent soil erosion it also works to add beneficial nutrients to the soil.
Finally, plants such as cowpea, comfrey, borage and chamomile will all add beneficial nutrients to the soil as they decay. These companions will need to be watered regularly, especially if you are growing in a quick drying, sandy soil.
Plants to Avoid
Avoid growing tall plants such as millet near a cashew tree. These can shade young saplings, stunting their growth.
How to Harvest and Store Fruit
When a cashew tree flowers depends on various conditions such as the weather and local climate. Even two plants growing next to each other may flower at different times. When your cashew tree does flower it will bloom for up to 3 months.
Once the flowers have been pollinated fruit will begin to form. This can take up to 8 weeks. You will first see the nut forming. In the 2 weeks before the fruit ripens the apple will enlarge. When the apple turns a dark pink or red, and the shell of the nut is a dark shade of gray, the fruit is ready to harvest.
The swelling and reddening of the apple is a sign that the fruit is ripening. Remember that as well as the nut, the apple is also edible.
Harvest the fruit as quickly as possible, especially if the weather is wet. Wet fruit may go rotten or, if left on the ground, begin to germinate.
Allow the nuts to dry before storing. Nuts can be stored in a cool, dry location for up to 2 years.
Processing Cashew Nuts
The nut sits in a shell filled with caustic oil. This oil can irritate or burn skin. You should wear gloves, long sleeved clothing and possibly safety glasses when opening the shells.
The safest way to process the shells is to freeze them. They can then be safely opened.
Take care when removing the nut from the kernel. It is surrounded by a caustic oil that can cause harm if it comes into contact with the skin.
The shells can also be roasted. Prior to roasting, soak the shells in water so that the kernel becomes slightly rubbery. This will help the shell to break snap, meaning the oil can safely drain away. Place the shells in hot oil, around 210°C for no more than two minutes. After removing the shells, place them in a bucket of cool water. Once cooled the shells can be opened and the nuts removed. Dry the nuts before storing.
While the kidney shaped shell houses the nut, the pear shaped pedicel is also edible. This swollen stem is known as the cashew apple. Rich in vitamin C this fruit is highly perishable. You can eat it fresh or juice it. They can also be used in syrups, wines, gins and pickles.
While the plant is mainly grown for its nut, remember that the apple is also worth using. The cashew tree also has ornamental properties, making it a worthwhile addition to the garden.
A cashew tree is an attractive, evergreen addition to any garden or orchard. It’s delicate pink flowers can add interest during the spring and summer months. Once established they require minimal care and attention, allowing you to enjoy their fruits and foliage.