Peanuts, also called groundnuts, have the highest protein of any fruit or vegetable, and they’re high in fibre and also free of cholesterol. Although they aren’t real nuts at all. Peanuts are the fruit of a legume, meaning they’re in the pea and bean family and they’re annuals so the plant only lasts one season. It’s surprisingly easy to grow peanuts in tropical through to warm temperate climates, and even in pots, so give it try!
Archeologists working on the mountain slopes of Brazil and Peru have discovered evidence of peanut farming dating back an amazing 7,600 years. In the USA, peanuts were mostly grown as animal fodder crops until the early 20th century. Peanuts were introduced into China about 400 years ago and they’ve become an important part of Chinese cooking, usually after being boiled. Peanut farming was introduced into Queensland, Australia, during the 1870s gold rush by Chinese migrants and they’re still widely grown around the South Burnett in its rich, open volcanic soils.
A peanut bush is about 50cm (20 inches) high and 1 metre (40 inches) wide. They bear small, yellow, pea-like flowers about one month after sowing. The flowers are self pollinating, and once that’s happened, the flowers quickly fade and shrivel. The ovary base inside the flower then begins to elongate into a long ‘peg’ shape, bending the whole flower stem downwards until it can poke its head into the soil. How weird is that?!
This below ground pod growth explains the plant’s botanical name Arachis hypogaea, as ‘hypogaea’ means ‘under the soil’. It takes about 10 days for the peg to reach the soil and push down under the soil surface. The tip of the peg then enlarges and turns horizontal, developing into a pod containing one to three kernels – or peanuts! This takes around 10-15 weeks.
Peanuts are a subtropical legume crop and need warm temperatures, frost-free conditions and plenty of water – about 500-600mm (18-24 inches) of rain or irrigation during their growing period. The good news is that they’re not too fussy about soil type or pH, as long as the drainage is OK. A very heavy clay soil will probably stay too wet, so you can plant in a wide pot or a raised bed. You should also check that there’s not lots of stones in the soil which can get in the way of the pods developing.
Peanuts are sown in spring to early summer in warm temperate to subtropical areas. In Australia, that’s from September to early January, but in tropical areas it’s best to wait until the dry season, from about April on. They’ve also been grown successfully in Western Australia and South Australia but in colder districts you’ll need to keep them in a pot in the warmest part of your garden.
While you can buy peanut bushes in pots, you can easily grow peanuts from seed if you buy a bag of raw peanuts (not roasted or salted), break them open and sow the kernels (seeds) about 3-5cm (1½ -2 inches) deep. Fresh peanuts are best and handle them very gently to make sure the skin around the seed stays intact; they should then germinate quite quickly in a week or two. And you won’t know what variety you’ve got, so it will be a surprise! As peanuts make a leafy groundcover that shades the soil, they can work well as a companion plant and weed suppressant for other crops, like sweet corn.
There are 3 main types of peanut plants – Virginia, Runner and Spanish. Virginia has large kernels so it’s popular for shell peanuts. Runner have smaller kernels and are used in cooking and making peanut butter. ‘Spanish’ types mature more quickly and will cope with heavier soils and are often used to make peanut butter and peanut oil, as they have a higher oil content. Some cultivars are better at resisting fungal diseases which can spoil the fruit.
There’s an odd thing about peanuts – the developing nuts take their calcium directly from the soil, not through the plant’s roots. So you’ll need to add calcium in the form of gypsum or dolomite just before flowering to make sure the pods develop properly. And don’t forget that peanuts needs plenty of water at every stage – through germination, flowering, pegging and pod enlargement. If they dry out it makes them more susceptible to alfatoxin, produced by the Aspergillus flavus fungus.
So how do you know when to dig up your peanuts? The clue is to watch for when the leaves start to turn brown, in late summer to early autumn/fall as the plant starting to die back is the sign that its fruit is mature. Dig up one or two and check for dark coloured pods inside the shell and that the peanuts have changed from a pinky colour to a golden colour. They should be ready to dig up 140-155 days after sowing.
To harvest your peanuts, you then need to dig up the whole peanut bush, shake off all the dirt and hang it upside down (so the peanuts are now at the top) to dry in a warm, dry place, like in the garage or garden shed. Once they’ve lost about 2/3rds of their moisture after 3-4 days, the stems become brittle, and you can break off the peanut pods, wash off any dirt and, if you like your peanuts raw, eat them! If you prefer roasted peanuts, spread them out on an oven tray and roast them at 160 degrees C (320º F) for 15-20 minutes if they’re already shelled, or for 20-25 minutes if they’re still in their shells.
So sadly, you can’t keep your peanut bush as it’s a totally destructive harvest method, but make sure to keep some raw peanuts to germinate for your next crop! Commercial peanut growers find the soil becomes depleted after peanut growing, so they rotate it with other crops.
Peanuts are a high energy food but release that slowly over several hours because of their high unsaturated fat content, and are high in niacin, vitamin E, folic acid and anti-oxidants, making them an ideal food.
Eat your peanuts raw or roasted, make your own peanut butter, use them boiled in Chinese dishes, or mix them up with chilli for a spicy sauce to go with south-east Asian satay. YUM!
Growing peanuts is a great gardening activity for kids – assuming they don’t have a peanut allergy. The seeds are large, they germinate quickly, the peanut bush doesn’t mind being watered a lot, and there’s the fun of watching the peg elongate and reach the soil and then the getting dirty and digging them up a few months later.
Storing peanuts – peanuts can become contaminated with alfatoxin if they are not stored properly in a cool (under 30ºC/ 85ºF), dry environment, so you should consume your harvested peanuts as soon as possible.
Sadly, peanut allergies have become increasingly common in developed countries, with severe reactions causing anaphylactic shock and even death. The latest research into this is finding correlations between the allergy and roasting peanuts (which is more popular in western countries) rather than eating them boiled or raw. There is also an association with changes in gut flora, perhaps brought about by increased hygiene and also concerned parents giving their children a later and low-dose introduction to peanuts which tends to create sensitivity rather than tolerance.
[NOTE – as with all home-grown vegetables, if you live in the city you should have your soil tested for heavy metals and toxic pesticide residues before you grow any food in it]