How to Grow Beautiful Organic Potatoes (pomme de terre) and Sweet Potato

Person planting different potato varieties in beds of hay and soil during a wet winter at the Seed Savers' Network Byron Bay, Australia

Potatoes, made famous by the Irish, due to their blight, and the Scottish, through their ambassador Ronald Mcdonald and his oddly named French Fries, actually originated in South America - joining a long list of edible Solanums from that region including tomatoes and some capsicums.

They were first thought to have been domesticated around 4000 BC by the inhabitants of the High Andes. Potato remains have been found in Chilca canyon south of Lima dating back to this period and definite evidence of cultivation has been found in northern and central Peru dating back to AD 1000. This comes in the form of unusual pottery, made by the coastal Moche culture, made in the shape of potatoes, which have been uncovered in burial sites.

The tuber was widely cultivated in Inca times, circa 1400, and was naturally freeze-dried and turned into what they call Chuno, a product which is still sold today. The process involves putting sliced or whole potatoes out in the cool dry mountain air for a time.

The first European experience of the humble spud dates from 1537 when Cieza de Leon travelled to present day Columbia, publishing his findings in 1553. Another description, written in the 1560s by Juan de Castellonos in his Elegias described the potato as being like a truffle, about the size of an egg, round or elongated, and white, purple or yellow, which were, "of good flavour, a delicacy of the Indians and a dainty dish even for the Spaniards".

Actual fair dinkum sightings of the potato in Europe were made by La Sangre hospital in Seville in 1573 which received them in an autumn vegetable supply, though this may have been the sweet potato.

potato flower

By 1601 it was reported by Clusius as being commonly grown in German and Italian gardens, and from there it spread throughout Europe (though Sir Francis Drake may have brought a few back to England from Virginia in 1586)

The early descriptions of potatoes grown in Europe were of a very tall plant with stems between 1.5 to 2 metres tall, which produced their tubers in late autumn, which is consistent with those wild ancestors of the Andes in Columbia, where flowers and tubers only form after the autumn equinox.

Modern potatoes can mature as early as July in the Northern hemisphere, and December/ January in the South.

Potato cultivation

Potatoes are usually cultivated by planting whole or segmented potatoes, which then multiply in the soil, according to conditions. One planted potato can produce anywhere from 4 to 30 new potatoes in a few months.

It is suggested that sprouting potatoes are used for planting - ie those which have started growing green stems - and it is also advisable to expose them to sunlight for twenty hours before planting.

For the home gardener you can try using potatoes bought from a vegetable seller (choosing the most healthy looking ones, without signs of damage), organic ones are generally better than others. It is also good to try planting a few different varieties to see which ones suit your particular area.

Generally these sprouted potatoes are planted in spring, after the last frosts in cooler areas, and are best harvested (for storage) when the green stems have flowered, then died. But you can also collect a few small ones before this has happened for cooking straight away -- these are called baby potatoes and they can be plucked from underneath the plant about 6-8 weeks after planting. Be careful not to expose the other potatoes though as they will turn green and stop growing.

Do not eat green potatoes, they are poisonous.

Once the potatoes have started to grow it is better to keep adding mulch such as straw or well-broken down compost around the stems of the plant, until you have quite a substantial mound over them -- making sure not to totally cover the green shoots. This will keep the growing potatoes being exposed to direct sunlight and should increase your crop.

Make sure to keep them well watered during the whole process, especially in places where you have long, hot, dry summers. But too much water may lead to disease, so make sure the soil is well drained.

Ideally your soil will have a high percentage of broken down organic matter added and be quite friable and easy to crumble. Very sandy soil, or very hard, compacted soil, should be avoided. In it's native South America potatoes can be found growing on rock ledges under leave mulch.

Search around for potatoes of all different colours and shapes, including black, bluish purple, red skinned varieties. There are thousands of different types.

Sweet Potatoes (Ipomoea batatas related to morning glories)

For sub-tropical climates it may be advisable to grow potatoes in winter, and it might also be advisable to just grow sweet potatoes, which are less work, and love long hot summers with high humidity.

Sweet potatoes can be grown in much the same way as potatoes but remember that they form a kind of ground cover, so need more space. They don't really need to be mounded either.

There are heaps of different sweet potato varieties for people with longer summers (not really Ireland I'm afraid, but southern United States is okay, as is Australia, ideally north of Coffs Harbour, NSW). Sweet potatoes require ample potash for a good crop and will mature within about 90 days in the tropics, they come in whites, reds and oranges and are pretty easy to grow. Try using them as ground cover in an orchard for instance (making sure to allow them a fair bit of sunlight, and to not place them too close to the tree's base - about two-three metres away from a small (not fully matured) mangoe tree (2-3 metres in height), or peach, or macadamia is okay, probably avoid citrus). Fertilise them well with potash and seaweed and manure solutions.

sweet potato leaves

Propagation is by pieces of sprouted tuber (similar to potatoes) or by separating stem cuttings later in the year. Place the pieces a few centimetres under the ground and wait for them to grow. You can also just put whole sweet poatoes in the ground in the same way. The stems sprawl over the ground and "dig in" to form more tubers as they go. The leaves are pointed and often 3 to 5 lobed at the base, as well as often being in the shape of a heart -- oh, how sweet.

Plant sprouted tubers in spring. Just the ones you get from markets are fine, trying again to get a few different colours and sizes to increase your chances of success. Once you've found one or two (or more) that thrive in your area you'll easily be able to grow as many as you can eat in just a couple of square metres.