The Cashew tree (Anacardium occidentale) is an attractive, flowering evergreen that native to Brazil. Introduced into India in the first half of the 16th century to aid afforestation efforts, these distinctive trees produce clusters of fragrant, rose-coloured flowers that grow into edible fruit. Interested in growing your own? Read on!
You may know the cashew tree for its nuts, but it also produces the cashew apple. Interestingly, both are part of the same fruit. If you look at the fruit of a cashew tree, you’ll see a pear-shaped fruit with a kidney-shaped shell attached to it.
The shell houses the familiar cashew nut. The pear-shaped pedicel is the swollen stem of the fruit, commonly known as the cashew apple. Perfectly edible, the apple is rich in vitamin C, containing around 5 times more than an orange, as well as iron, vitamin B1, and calcium.
How to Grow a Cashew Tree
Cashew trees, categorized in the USDA Zones 10-11, are native to tropical, warm areas. They do best in areas where the daytime temperature averages about 77°F.
They can be grown in cooler climates, but ideally, the temperature shouldn’t regularly drop below 50°F. Cold weather protection can help to protect them against cold snaps, but a deep freeze will kill them off.
Trees grown from seed will take up to three years to bear fruit. A quicker method is to purchase a grafted cashew tree: these tend to bear fruit within 18 months. It’ll take up to seven years before your trees can produce their optimum yield.
Growing a Cashew Tree from Seed
Germination is an easy process: just make sure that you use fresh cashew seeds. (A cashew seed is the cashew nut still inside the kernel.) The seed should be no more than four months old—any older and it won’t germinate. Dry fresh seeds in the sun for three days before sowing.
Start cashew seeds in pots, instead of planting them straight into the ground. By doing this, you can give them a bit of extra attention and protection. You can sow seeds into pots at any time of year, as they’ll will grow happily in pots until they’re ready to be planted out.
Sow cashew seeds either into smaller individual pots or into one larger pot. Sowing more than one seed increases ther chances of producing a healthy cashew tree. Weaker seedlings can be thinned out later on.
The pot should be clean and have drainage holes in the bottom. Cashew tree seedlings are prone to phytophthora root rot. This means that they shouldn’t be allowed to sit in overly wet soil. If there are no drainage holes in your pot, you’ll need to drill some into the bottom.
Fill the Planter with Fresh Compost
A good, general purpose potting compost will be fine. Mix a handful of vermiculite into the soil to help to improve nutrient and moisture retention. Leave a gap of about 1 inch at the top.
Place the seeds in the pot at a slight angle, and at a depth of 5- 10cm. Cover with fresh soil and water in. Keep the pots in a warm, light location. Don’t place them in direct sunlight: too much heat can burn seedling leaves and cause plants to fail. The pots should also be regularly checked to ensure that they don’t dry out.
Germination will take anywhere from four days to three weeks.
As the seedlings grow, make sure that they get plenty of light and water. If you’re unsure of how much water to give a plant, try watering it over a sink or bucket. When water begins to drip through the drainage holes, the soil has taken on enough moisture and you can stop watering.
Planting out Cashew Trees
As the cashew trees begin to outgrow their pots, it’s time to plant them out. The best time to do this is in the spring, as this gives the tree plenty of time to establish itself before winter.
Before you plant out the young trees, allow the plants to harden off for a couple of weeks. This acclimatization period is a vital step in helping tender plants thrive in their new environment.
Positioning your Tree
Position your tree in sandy or sandy-loam soil with a pH level between 5 and 6.5. That said, cashew trees will grow well in most soils as long as it they’re well draining.
The one soil type you should avoid planting your tree in is heavy, clay soil. This soil type tends to retain moisture, meaning that it can easily become waterlogged. Cashew trees that sit in waterlogged soil will almost certainly develop root rot.
The ideal location for your tree is a frost-free spot that faces south or west. It should be protected from strong winds. The location should also be sunny, receiving at least 6 hours of light a day. While cashew trees can grow in shady spots, they’ll struggle to produce fruit in those conditions.
Planting the Tree
Rake the area carefully, and make sure that you remove any weeds. They’ll rob your cashew tree of vital nutrients and moisture, and large rocks from the area.
Dig a hole large enough to comfortably hold the sapling’s entire root ball. When removing the sapling from the pot, it’s vital that you don’t disturb the root system. Damaging it can lead to the plant struggling to establish itself, or even dying.
If you’re planting more than one cashew tree, remember that they’re not only vigorous growers, but also have extensive root system. Basically, they like their space. Mature cashew trees will require an all-round gap of 10m. When the trees are young, they can be planted at distance of 8x5m and thinned out later.
After filling in the hole, water well. Young cashew trees should be staked or given some form of support.
Temperature and Positioning
As we’ve already discussed, cashew trees are native to tropical regions, so they’re very vulnerable to frosts. Generally cashew trees will struggle to survive without protection when the temperature drops below 50°F. Therefore, you’ll need to take precautions to protect your tree from cold spells.
You should plant your tree either near a warm south- or west-facing building wall, or on a sloping incline facing either direction. Either measure will lessen the possibility of frost and cold weather damage. South and westerly facing locations tend to receive more warmth, and aren’t as frost-prone as north- or east-facing locations.
Add a 2-3 inch layer of organic mulch around the base of the tree to help to protect the root system from frosts. Renew these mulch layers regularly to ensure continued protection.
Cashew trees are fairly drought tolerant, especially once established. Of course, regular watering is still needed, particularly for young trees. A weekly watering will double the growth rate, allowing the trees to establish themselves more quickly. Regular watering also encourages fruit production.
In warmer climates you may need to water your trees twice a week. Be careful not to over water, as doing so can harm or even kill the plants. It’s best to wait until the soil around the base of the cashew tree feels dry before giving it a drink.
You should also cease watering temporarily after periods of heavy rain. Too much water can not only lead to root rot, but can also cause nuts to rot or fallen nuts around the tree’s base to start germinating.
Cashew trees require less watering in wintertime than during the spring and summer. You may even be able to cease watering completely for a time. As the weather warms up again, gradually increase the regularity of your watering routine.
Mulching the base of your cashew tree will help to protect it from frosts and cold weather. It can also discourage weeds from growing and help the soil conserve moisture. In fact, this is particularly helpful in sandy soils. Mulch can also help to protect plants from soil-borne pests.
If you don’t want to regularly work organic matter around your tree, black polythene covers can be placed around its base. While this won’t provide the extra nutrients that come with organic mulch, it’ll aid moisture retention and help protect against frosts.
Alternatively, stones and small pebbles can be placed around the tree’s base. These are more attractive than the black plastic covering, but are just as beneficial.
Fertilizing Cashew Trees
Regular fertilization during the growing period, particularly when the trees are in flowering and are developing their fruit.
The fertilizer that you use should contain nitrogen, phosphorus, and zinc. For best results, try a slow-release fertilizer with a NPK 8-3-9 ratio. This combination contains all the nutrients that a cashew tree needs.
The amount you apply will depend on the size of the tree and its growing conditions. Consult the instructions on the packet to work out the exact amount. Generally you will need to fertilize your tree once every two months during the growing season.
You can also work compost or farm manure into the soil around the base of mature cashew trees once a year.
Pruning and Training Cashew Trees
Remove any sprouts that come from the roots during the first year, as the cashew tree works to establish itself. If allowed to grow, these sprouts will take up valuable nutrients that could instead help the tree to grow.
Regularly remove any branches that are broken or appear diseased. This will prevent diseases from spreading and discourage pests from targeting your trees. Also remove tangled and overcrowded branches to encourage growth.
Train cashew tree branches during the first few years to take on a proper shape. This shaping will largely involve removing lower and tangled branches. The ideal time for pruning is during the late summer and early autumn.
Smear any cut surfaces with Bordeaux paste to prevent mildew, mold and fungal infestations.
Regularly remove weeds that are growing at the base of the cashew tree. This enables more moisture and nutrients to get to the tree.
Mulching, or if you have a line of cashew trees, growing grass strips between the tree lines will prevent erosion and discourage weed growth. Grass strips will require regular mowing.
Common Cashew Tree Problems and How to Solve Them
Healthy cashew trees will generally be free from pests and problems. There are, however, a few things that you need to look out for.
These trees are prone to zinc deficiency. Sandy soils, in which cashew trees flourish, often struggle to retain ample zine amounts. If caught early enough, this type of deficiency is easy to fix.
Spraying the leaves with a micronutrient foliar zinc fertilizer can help to alleviate deficiency. An organic alternative is to apply kelp extract. Cashew trees happily tolerate high zinc levels, so don’t worry about overdoing it.
While it can be easy to fix, this type of deficiency can be difficult to diagnose. The symptoms—chlorosis or leaf discoloration—are similar to signs of other nutrient deficiencies. One way in which zinc deficiency differs from others is that it usually becomes apparent on the plant’s lower leaves first.
Other nutrient deficiencies tend to initially manifest on the plant’s top leaves. The only way to confirm a zinc deficiency is to test soil levels.
The most common method boosting soil levels is to work in chelated zinc. Add compost or other organic matter to the soil on a regular basis helps to maintain all nutrient levels.
Cashew Tree Companion Plants
- Legumes, such as beans or peanuts, are popular companion plants. In fact, leguminous cover can help to enrich the soil around your cashew trees with various nutrients. It’ll also help to maintain soil moisture levels.
- Borage, comfrey, chamomile, and cowpea will also add nutrients to the soil as they decay. To establish these plants properly, make sure that you water them regularly. This is especially important if they’re sitting in sandy soil that struggles to retain moisture.
- Casuarina and coconut are also both popular companion plants for cashew trees. Not only do they help to keep nutrients in the soil, they enjoy similar growing conditions.
Plants Cashew Trees Dislike
- Millet, sorghum, and other tall inter crops should be avoided. These can stand taller than your young trees, causing shade and stunting growth.
Cashew trees will generally be pest free as long as they are in good health.
Occasionally they’ll come under attack from Tea Mosquitos, Leaf Miners, Blossom Webber, Fruit and Nut Borers, and Stem Borers. The majority of these pests can be controlled by applying fungicide or, in the case of the Fruit and Nut Borer, stem grease.
The most difficult pest to get rid of is the Western Flower Thrip. This pest has developed a resistance to many pesticides. so you may need to treat the tree more than once.
How to Harvest and Store Cashew Tree Fruits
Flowering can vary depending on the weather and climate. It can also vary from tree to tree. Two trees next to each other—that you treat exactly the same—can flower at different rates. When your tree does flower, it’ll be in bloom for up to three months.
From the point of pollination, it’ll take between six and eight weeks for the fruit to develop. The cashew nut will develop first, and the cashew apple will enlarge significantly in the final 2 weeks before ripening. The fruit will be ready to harvest when it turns dark pink or red, and the shell is a darker shade of grey.
Allow wet nuts to dry fully before storing. You can store unprocessed nuts in a cool, dry location for up to 2 years.
Processing Cashew Nuts
The cashew nut forms in a shell that contains a caustic oil. If this oil comes into contact with your skin, it can cause irritation or burns. As such, you’ll need to protect yourself when processing the nuts.
The safest method is to freeze them, after which point you can safely remove them from their shells. You should still wear a long-sleeved shirt, gloves, and maybe safety glasses just in case.
Alternatively you can roast the nuts.
Before roasting, soak the cashew nuts in water. This makes the kernel slightly rubbery and also helps to rupture the shell, allowing the oil to drain away safely.
Heat the oil to 210°C in a large pan. Drop the nuts—still in their shells—into the oil for two minutes. Any longer and they’ll become too brittle. Note that the nuts may squirt out the caustic liquid when dropped in the oil, so wear protective gear.
When the nuts are ready, place them in a bucket of water to cool. They can then be removed from the shell and dried.
A Few Additional Notes
If you only end up with a few edible nuts the first time, don’t worry. It often takes a few attempts before you get the technique right.
Cashew nuts can be eaten raw, but make sure that they’ve been cleaned and aren’t contaminated with any caustic liquid. Remember that the apple part of the fruit is also edible. This highly perishable fruit is used in pickles, gin, syrup, and wine, but can also be eaten fresh from the tree.
A cashew tree is an attractive addition to any garden, with its rich green leaves and delicate pink flowers. It’s also an easy tree to grow and cultivate. Once established, it’ll require minimal attention, meaning that you’ll be able to enjoy its fruits for many years to come.