Cashew Family

Exquisite nuts or toxic leaves, how much do you know about the cashew family?

Cashew nuts still attached to the tree (Vinayaraj) CC BY-SA 3.0

Expensive, delicious, and nutritious, cashews (Anacardium occidentale) are treat that you just might be able to grow at home. Before you start planting, however, there is more to the cashew family than meets the eye. 

Cashew fruits and nuts

In most cases, these trees, shrubs and vines have female and bisexual flowers while others have male and bisexual flowers. If you want to grow your own, you will probably need two or more plants, with one of each gender.

Did you know that those delicious cashew nuts are not really nuts at all? Instead, they are drupes, much like the pits found in stone fruits, such as almonds, cherries, and peaches. In the same way that those trees, fig trees, strawberries, and pineapples produce accessory fruits, cashew trees do, too. The only difference is that cashew nuts hang underneath their accessory fruits, known as cashew apples. Cashew apples are used to make sweet, astringent drinks and liquor.

Young cashew fruits (Vinayaraj) CC BY-SA 3.0

If you start taking a cashew drupe apart, you will find that the seed coat is very thin and that there is little or no endosperm, also like a strawberry. [You can think of a seed using endosperm to grow the same way we would use a peanut butter sandwich, while accessory fruits are more like drinking juice - both cases provide nutrition, but in different ways.] Before you try this, be sure to don some rubber gloves. More on that in a minute.

Ripe cashew apples (Abhishek Jacob) CC BY-SA 3.0

Members of the cashew family

There are hundreds of members of the cashew or sumac family. Along with delicious cashews, the cashew family includes some favorite edibles, and a few you may not have heard of before:

• mangos (Mangifera indica)
• pistachios (Pistacia vera)
• hog plums, aka Tahitian apples, Jamaican plums (Spondias dulcis, S. mombin, and S. purpurea) - tropical fruit often sold pickled with chili
• kaffir plum, aka wild plum (Harpephyllum caffrum) - from Africa
• marula (Sclerocarya birrea) - from Africa
• Peruvian pepper trees (Schinus molle) - commonly planted as sidewalk ornamentals; not true black pepper plants, though their pink fruits are often sold as pink peppercorns
• sumac spice (Rhus coriaria) - powdered drupes give a tart, lemony flavor to Arab cuisine

Here, in North American, smooth sumac (Rhus glabra) and stag horn sumac (R. typhina) are used to make a drink called “sumac-ade”. The cashew family also includes mastic trees (Pistacia lentiscus) and varnish trees (Toxicodendron vernicifluum), which are the trees that give us varnish, lacquer, and useful oils. Natural varnish is made from tree resin.

Like many other families, there is heated debate about who belongs and who does not. Not too long ago, pistachio plants were brought into the cashew fold, but there are still discussions about this in scientific corners. Cashew family taxonomy includes dozens of genera, most of which are not edible. Watch out, though - some of them might try to hurt you!

Cashews - beware!

Did you know that raw cashews are poisonous? They are. They contain the same chemical found in poison ivy, poison oak, and poison sumac. That’s because they are all in the same family! The sap of all cashew family plants, called urushiol, is something to be reckoned with as it can be highly toxic. Just under the bark, these plants have resin canals filled with the stuff. ​

Pacific poison oak (Eekster) CC BY-SA 3.0

Atlantic poison oak (USDA) Public Domain

Poison ivy (D. Gordon E. Robertson) CC BY-SA 3.0

Poison sumac (Freekee) Public Domain

If that weren’t bad enough, the seed coat of cashew drupes contains a toxic oil that is acidic enough to burn your skin. If you are still interested in growing your own cashews, read on. If not, read on anyway! Who knows what you’ll learn?

How to grow cashews

Being native to tropical and subtropical places such as India, Thailand, Sri Lanka, and Papua New Guinea, cashew tree might be difficult to grow, depending on your Hardiness Zone. If you are determined, however, it can be done. Keep in mind, before you get started, that mature, full-sized cashew trees can grow to nearly 50 feet in height. Dwarf varieties are far more manageable at only 20 feet.

Cashew trees prefer loose, sandy soil with plenty of sun and excellent drainage. Do not try using grocery store seeds - they are not viable. You will need to get seeds from a reputable supplier. Viable seeds should be planted 4 inches deep and about 30 feet away from each other. These plants can handle temperatures as high as 122°F, but cold and damp will be the death of them. Heavy, soggy clay soil nearly always causes root rot in cashew trees. They don’t handle wind very well, either, so be sure to provide tree supports while trees are young and do not plant them in windy areas.

Keep your young tree properly irrigated and feed trees twice a year using a mix determined appropriate by your soil test results. Generally speaking, cashew trees use a lot of nitrogen, phosphorus, and zinc. After 3 or 4 years, you should be able to harvest your first crop of cashews. You will know your crop is ready to harvest when the cashew apple is either red or yellow and the drupe shell has turned gray.

Hog plums (Forest & Kim Starr) CC BY 3.0

Peruvian pepper tree (Liz Upton) CC BY 2.5

Cashew tree (MJEHermann) CC BY-SA 4.0

Before you start nibbling, however, remember that the seed coat of cashew drupes contains a toxic oil. You will need to roast those nuts in a covered container at 375°F for 10 to 20 minutes. Traditionally, they are roasted covered in sand. Apparently, the toxins released as fumes during this process will ruin your cookie sheet or whatever lid you opted for, so choose accordingly and be sure to ventilate the area as you work. Since the oils within cashew shells is extremely acidic, it can burn your skin, so wear long sleeves and eye protection.

Next, shake the nuts in a sieve, if they were roasted in sand, and then wash them in soapy water to remove any residual toxins. Crack open your priceless cashews now and use a knife to remove the thin seed hull. Finally, saute your cashews in oil at 300°F for 5 minutes or so to neutralize any last bits of toxins.

Did you know that cashew shells have been used to make lubricants, paint, and military arms?
I didn’t either.

I think I’m beginning to understand why cashews are so expensive…

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For anyone unlucky enough to have a chance meeting with poison ivy (Toxicodendron radicans), Pacific poison oak (T. pubescens), Atlantic poison oak (T. diversilobum), or poison sumac (T. vernix), you know all too well how those plants can make you devastatingly uncomfortable. Believe me, I speak from experience.

"Leaves of three, let it be; berries white, take flight; root hairs red, recoil"
​
[I made up that last bit.]