Tree · Anacardiaceae
Cashew
Anacardium occidentale
A warm-rooted tropical tree that carries two harvests on one branch: the fleshy cashew apple above and the kidney-shaped nut hanging below, where it stays sunny and well drained.
Full sun
Every 7–14 days
USDA 10–13
20–39 ft · 6–12 m
Overview
The cashew is a fast-growing tropical tree in the same family as poison ivy and mango, native to the warm lowlands of Brazil and now grown wherever frost stays away. Heat is its engine and cold its undoing, so it survives only in the warmest zones. Left room, it builds into a broad, low-branching tree that can rise past 40 feet (12 m), its wide canopy spreading nearly as far across as the tree is tall.
Up close the fruit is an odd, two-part thing. The plump, fleshy red or yellow swelling is the cashew apple, a thickened stalk rather than the true fruit, and the hard, kidney-shaped nut dangles from its lower tip, on the outside. That curved, gray-shelled nut is the prize, yet the shell wrapping it is steeped in a caustic oil that must be cooked away before the pale kernel inside is fit to eat.
For all its size, the cashew gets by on very little once its roots are set. It puts on growth in poor, sandy ground that would starve other trees, and it shrugs off drought after the first few years. The single thing it will not tolerate is wet feet, so fast-draining soil counts for far more than rich earth from the moment it goes in.
Care
The short version: plant it in full sun in deep, sandy, fast-draining ground. Water it steadily only while it is young, then ease off as it matures. Keep it warm and frost-free, and never let the roots sit in soggy soil.
Light
The cashew wants full sun and bears poorly in shade, so set it in an open, bright spot with nothing throwing shadow over the broad crown. Strong light is what keeps the flower clusters opening and the young nuts swelling.
Water
Young trees want frequent water while their roots reach out, then much less, because a mature cashew is highly drought tolerant and dislikes soggy ground. Let the top half of the soil dry out between drinks, around every 7 to 14 days, and keep it leaning toward dry.
Soil
Give it deep, well-drained sandy or sandy-loam soil, even the lean, low-fertility kind that stalls other trees. A pH of 5.0 to 6.5 suits it, and quick drainage matters far more than rich ground.
Temperature
This is a true tropical tree, comfortable from 50°F to 104°F (10°C to 40°C) and killed by frost. Keep it only where cold never settles in, in tropical or frost-free subtropical climates.
Humidity
The cashew favors humid air, around 50% to 80%, like the tropics it sprang from. Even then, an open canopy that lets the broad leaves dry off keeps disease from settling on them.
Feeding
Through the warm growing season it takes a balanced NPK of nitrogen, phosphorus, and potassium, with zinc added where the soil runs short. One seasonal feeding is enough for so tough a tree.
Pruning
Train a young tree to a single strong leader, then cut away the dead, diseased, crossing, and low limbs. Opening the dense crown lets air drift through the leaves, the best defense against the fungal diseases cashews are prone to.
Repotting
A field-grown cashew stays put for years, while a potted one wants a larger container every 2 to 3 years. Roots circling the pot, water running straight through, and new shoots that stall all signal it has outgrown its home.
Size & spacing
A common cashew fills out into a broad tree of 20 to 40 feet (6 to 12 m) tall and nearly as wide, so it asks for real room. Place it well clear of buildings, paths, and power lines, since the spreading crown can reach 33 feet (10 m) from side to side.
When to plant
The cashew follows tropical seasons rather than a temperate calendar. Start the nuts in nursery bags a couple of months ahead, move the young trees out once the soil has warmed and frost is past, then watch the flower clusters open in the dry season, with nuts and apples filling in a few months behind them.
Northern hemisphere
Southern hemisphere
Typical months for a temperate climate: start earlier in warm zones, later where spring frosts linger.
- Sow: Seeds sown in nursery bags 2 to 3 months before transplanting in warm climates
- Plant: After all frost danger when soil is warm; tropical and frost-free subtropical regions only
- Harvest: Flowers in dry season; nuts and cashew apples harvested several months later, typically late dry season
Hardiness
USDA hardiness zones: 10–13
Temperature: down to -1°C
Troubleshooting
Cashew problems tend to surface first on the soft new flushes, the flower clusters, or down at the roots, and lingering damp is usually what triggers them. Spotted early, a fungicide or sharper drainage settles things. Match the look of what you see to the symptoms below before the trouble works its way through the canopy.
Black, sunken spots on leaves and shoots with dying twigs
Those dark, sunken lesions pressing into the leaves, shoots, and young nuts are anthracnose, a fungus that takes hold when warm air stays wet and the fresh flushes and flower clusters hang damp for hours. Cut out and destroy the marked shoots, thin the crown so air moves through, and apply a labeled fungicide as the tree flushes and flowers. Wide spacing and dry foliage stop most of it before the dark spots ever appear.
Fix:
- Prune and destroy infected shoots
- Improve canopy air circulation
- Apply a labeled fungicide during susceptible flushing and flowering
Wilting, scorched leaves where the soil stays wet and soggy
Leaves that wilt and scorch brown while almost no fruit sets in heavy, waterlogged ground point to root rot, not drought, with the roots themselves turning dark and discolored. The slide shows up right after heavy watering or standing water. Sharpen the drainage, cut back the watering, and on heavy soils lift the tree onto a raised mound. A mature cashew shrugs off dry spells, so soaked roots are the real threat.
Fix:
- Improve drainage
- Reduce irrigation
- Plant on mounds in heavy soils
Grayish-white powder dusting flowers and tender new nuts
A grayish-white powdery film coating the flower clusters and the tender young nuts is powdery mildew, which settles onto soft new growth during cool, dry flowering spells. Left alone, it drops flowers and small nuts and thins the crop. Dust with sulfur or a labeled fungicide at flowering, strip off the worst-coated clusters, and keep the crown open.
Fix:
- Apply sulfur or a labeled fungicide at flowering
- Remove badly affected panicles
Toxicity
The roasted, shelled kernel is a safe snack, but the raw nut is a different creature. The hard outer shell and the thin papery layer hugging the kernel are loaded with a caustic oil called CNSL, dark, sticky, and carrying the same urushiol found in poison ivy, which scorches skin and mouth on contact. Keep raw shells, husks, sap, and prunings clear of children and pets, and handle them only in gloves.
Toxic to
Cats · Dogs · Horses · Rabbits · Livestock · Birds
Safe for
People
Cats Caution
The rich, oily kernel brings on drooling, vomiting, and loose stools, and a cat that licks or bites the raw shell can scald its mouth on the caustic oil weeping from it. Keep both well out of reach.
Dogs Caution
A few stolen nuts usually mean vomiting and diarrhea, and a bigger helping of the fatty kernel can trigger painful pancreatitis. Gnawing the raw shell adds urushiol burns across the mouth and skin.
Horses Caution
Horses should stay clear of the raw shells, the sticky sap, and the prunings, where the same urushiol that scars human skin can blister the soft lips and mouth. Clear fallen shells and trimmings out of any paddock.
Rabbits Caution
The caustic shell oil and the dense, fatty nut are both wrong for a rabbit's gut. Offer neither, and watch for soft stools or a stalled appetite if one gets into dropped shells.
Livestock Caution
Cattle, goats, and sheep can scorch their mouths on the raw shell liquid and sour their stomachs on the oily kernels. Fence stock away from the tree and rake up the scattered shell waste after harvest.
Birds Caution
Backyard birds should never get the raw shells or husks, since the irritant oil burns soft tissue. A crumb of plain roasted kernel now and then does no harm, though the fat does them no favors.
People Roasted nuts safe
Properly roasted and shelled cashews are a wholesome snack and safe to eat. The raw nut and its shell are another matter, since the urushiol they carry is the same irritant as poison ivy and burns skin and mouth, which is why nobody should handle or eat them unprocessed.
Wear gloves when handling raw shells, husks or sap; never let people or pets contact or chew unprocessed nuts. Roasting in the open can release irritant fumes.
Helpline numbers
United States
ASPCA Animal Poison Control: (888) 426-4435 (fee applies)
United Kingdom
Animal PoisonLine: 01202 509000 (fee applies)
Australia
Animal Poisons Helpline: 1300 869 738
Varieties
Cashews are sorted mostly by how big they grow and how quickly they start to bear, and two broad forms account for most of what you will run into.
Common (medium/tall) cashew
The common medium to tall cashew is the traditional plantation tree, a broad, spreading giant that reaches 12 m or more and is slow to begin bearing.
Dwarf precocious cashew (e.g. anao precoce types)
Dwarf precocious cashews, such as the anao precoce types, are compact, low-growing selections that flower and fruit within a few years and stay small enough to plant close and pick easily.
How to propagate
A cashew comes either from a fresh nut or from a clone of a tree someone has chosen, and the path you pick decides how soon it fruits and how faithfully it copies its parent.
SeedEasy
Sow fresh viable nuts in the warm season · Germinates in 2 to 3 weeks; bears in about 3 years
Seed. Sow fresh, viable nuts in the warm season, keeping the curved, kidney-shaped ones that sink in water, and the seedlings break the surface in 2 to 3 weeks. Drop them straight into the ground or into bags, since the long, deep taproot resents being moved once it forms. Seedlings differ one from the next, and a tree raised this way takes about 3 years to start bearing.
GraftingModerate
Onto vigorous seedling rootstock in warm conditions · Bears in roughly 2 to 3 years
Grafting. Joining a chosen clone onto a vigorous seedling rootstock in warm weather gives uniform trees that crop sooner. A softwood, cleft, or veneer graft is the usual union, and the tree bears in roughly 2 to 3 years.
Air layeringModerate
Warm humid growing season · Several weeks to root before severing
Air-layering. Air-layering through the warm, humid growing season makes a clone of the parent tree. The wrapped stem needs several weeks to push roots before it is cut free, and the method sees far less use than grafting on a commercial scale.
Myths
The cashews labeled raw in stores are genuinely raw, and any nut straight off the tree is edible.
Cashews sold as raw have already been steamed or heat-treated and shelled before they reach the shelf. A nut pulled straight from the tree still holds caustic shell oil, the urushiol and anacardic acid that burn skin and mouth. No cashew is safe to eat or handle until it has been roasted and processed.
The fleshy red or yellow cashew apple is the fruit, with the nut tucked inside it.
The plump, juicy cashew apple is not the true fruit at all but a swollen stalk, an accessory fruit the tree puffs out below the flower. The real fruit is the kidney-shaped nut hanging outside and below the apple, never enclosed within it.