How Peanuts are Grown
Peanuts are legumes with a very unique growth cycle. There are four principal varieties under commercial cultivation around the world: Virginia, Runner, Spanish, and Valencia.
Virginia and Runner peanuts are low, bushy plants which have two large seeds per pod. Spanish and Valencia are more erect and have smaller seeds. Each different variety is suited to certain soils and climatic conditions - and today, Australian agricultural scientists are developing a wide range of sub-types of these four basic variants to extend the plants further.
In the USA, peanuts are also widely known as goobers, goober peas, ground peas, ground nuts or earth nuts. Here in Australia, though, we generally call them peanuts wherever they're grown and regardless of the variety being cultivated.
Peanuts grow best in loose, well-drained soils. Some species do better under irrigation but others manage quite well in fairly dry climates.
However, all types of peanuts do poorly in badly drained or tight, clay soils. And all types are susceptible to frosts.
As a result, peanuts tend to be grown over the Spring and Summer months in northern Australia. The main types grown in the South Burnett are Red Spanish and Virginia peanuts and these usually require a minimum of 120 to 150 days to reach maturity.
Furthermore - because yields can drop by 10% each time if the plants are continuously cultivated (right down to 60% below a full yield) - peanuts tend to be grown in rotation with other crops anywhere they're farmed.
In Bundaberg and Childers, for instance, they're often rotated with sugar cane.
Peanuts are usually planted in rows, 6 to 10 plants per metre. Seeds are lodged just a few centimetres below the soil and the young plants usually emerge within a few weeks of seed planting. They generally begin to bloom about 30 to 40 days after that.
Peanut plant flowers are small, bright yellow and pea-like in appearance. After pollination and fertilization of the flowers occurs, the stalk (peg) below the fertilised plant ovary elongates and curves downward towards the soil.
It usually takes about 10 days after fertilisation for this "peg" to penetrate into the soil.
Then - about a week after soil penetration - this peg tip enlarges and pod and seed development begin. The fruit (ie peanuts) then matures over the next 9 to 10 weeks.
Peanut harvesting generally occurs when the foliage begins to yellow in late Summer and/or early Autumn.
Harvested plants are usually allowed to dry for several days before being shelled and roasted. This is because raw peanuts (taken straight from the ground) contain a very mild toxin. To eliminate it, peanuts are dried as the final stage of the production process to prepare them for consumption.
In Australia, peanuts can also be subject to all manner of pests. The worst of these is aflatoxin (a fungus) but insects and weeds can also pose problems. Peanut farmers need to care for their crops continuously over the growing cycle.
Most peanuts also need lots of calcium in the soil to develop good nuts (which is usually supplied with gypsum).
And although peanuts can generally make good use of any fertilisers left over from other crops - making them a great "soil cleaner" - some calcium top-up is usually necessary to ensure that the nuts develop fully before any new crop is planted