POTATOES (solanum tuberosum)
Potatoes are one of the oldest crops cultivated by early man some 5000 years B.C., high in the Andes round Lake Titicaca. The Incas selected more palliative strains of the wild potatoes for a staple food. Brought to England in 1590, they did not become a food staple here until the late 18 th century, after the potato adapted to our long summer days. As most of the nutrients are in or just under the skin, just scrub the skin and remove blemishes, including green bits, for the most food value. The poisonous green bits will give you stomach upsets, and are caused by light reaching the potato for some time.
Select varieties of potatoes to have potatoes in season for as long a period as possible, and for different uses. For the earliest potatoes, try planting a 1st early variety in a large container in the greenhouse or cold frame in February, covered in fleece to prevent frost damage, for eating in early June. Then follow with 1st and second early varieties outdoors, and then finally main crop varieties. Time from planting to harvest is from three to four months.
The different uses are for Salads (small and waxy), floury for roasting and chips, waxy for general use, and the heritage ones with coloured flesh, for novelty (microwave or steam to retain the colour). It is most economical to choose medium sized tubers, if you have a choice.
Chitting of the tubers is recommended to get the potatoes off to a flying start. Chitting should advance the crop by some 2 weeks for earlies. Place the tubers upright in old egg boxes or trays in a cool, light, frost-free place until the shoots are about 1 cm long.
Traditionally, plant the tubers with the shoots up-most, in fertile soil about 20 cm deep, about 40 cm apart, with the rows about 50 cm apart. Plant out your earlies in early March, provided the weather is mild, with the rest of the potatoes being planted out at the beginning of April, but you may have to delay planting if weather conditions are not favourable.
Alternatively, if planting through fabric to cut down on weeding using my methods, see Maintenance and cultivation.
During the growing season keep the potatoes weed-free. Earth up the potatoes when they are about 10 cm high, If you are using the traditional growing method. Many potato varieties will flower and produce round, green seed pods, which are poisonous and must not be eaten. If April, May and June are very dry, you may have to water the potatoes to keep them growing. After that, do not apply water in case the dampness encourages Blight, the disease that caused the Irish Potato famine in 1845-1849, and the death of 1,000,000 people.
For the earliest outdoor potatoes, choose suitable well chitted, first early varieties.To speed up their growth, if you plant a short stemmed potato, such as “Swift”, it is possible to grow them under polythene or fleece. Make sure that the potatoes have continuous adequate moisture while they are growing under cover, or they will split. Try and protect the potato foliage if frost is expected. They will usually recover and continue to grow even if the foliage has been frosted.
Potatoes start to die down naturally when they are ready to be harvested. The foliage goes yellow and you can confirm that they are ready by gently lifting the potatoes with a fork. Carefully lift the potatoes, wash them, and leave them in the air to dry off for and hour or so. Those potatoes that are going to be used in the next 3 or 4 weeks, put them into a mesh sack in a cool, airy, dark place and use as necessary. Never store them in plastic bags, as they will go rotten very quickly.
The long term storage of potatoes, say to March and April, is difficult for the amateur. Commercially, special temperature and humidity controlled storage is used, or horror of horrors, they are sprayed with a chemical after they have been lifted, to prevent the potato sprouting! Storage is easier if the potato variety has a long period of dormancy, i.e., is naturally slow to start sprouting, like Axona. Generally, you should eat the earlies first, and the others before they start sprouting.
Try leaving some main crop potatoes in the ground with an extra 30 cm of soil placed on top to prevent frost damage, for digging up in March and April when the Supermarket ones are poor.
Saving your own seed potatoes is not recommended, unless you know what you are doing. Choose only medium sized tubers, with absolutely no sign of any disease. Similarly, check over all bought seed potatoes and discard any diseased ones. Wash your hands after handling any seed potatoes that have been treated with fungicide powder.
Do not plant supermarket potatoes as seed potatoes, as these have frequently been treated to prevent them sprouting or growing, and they are not certified disease-free stock.
Recent independent tests growing potatoes using supermarket potatoes as seed potatoes, gave alarming results.
Most supermarket potatoes including organic ones, were much slower to sprout, probably due to treatment with sprouting inhibitor chemicals. Once in the ground, you want the potatoes to grow as quickly as possible to prevent rotting of the tubers. About 20% of the supermarket potatoes in the tests, rotted in the ground and produced no crop.
For some of the supermarket varieties tested, the crop yield was half that produced by proper seed potatoes grown as a control.
Some two thirds of the supermarket potatoes were infected with a virus, and you do not want to bring viruses into your ground. Because of the dangers of bringing disease into the U.K., it is actually illegal to plant potatoes from outside the E.U. and Switzerland, even though they are available for eating from supermarkets.
The taste of individual varieties of potatoes is very subjective to the individual person and the way that the potatoes have been cooked, as well as the age of the potatoes. Boiling potatoes leaches out a lot of the flavour, colour and vitamins. Just try boiling Highland Red or Salad Blue potatoes and watch the colour leach out. Micro wave cooking gives the best results to my taste buds and gives superb results for floury potatoes. When potatoes are picked while they are still immature, i.e., the skins can be rubbed off easily with a finger, the taste can be quite sweet. Later, when more mature, i.e., the skin is rough and firm, potatoes become more earthy in taste. After several months storage in a cool, dark place, the taste can become more intense, as some of the moisture will have evaporated away.
Best early varieties for taste, texture and early cropping, from independent tests.
Lady Christl. The early oval tubers cropped early and the smooth, yellow waxy flesh, had a good taste. Not the biggest crop.
Casablanca. High yielding, with a creamy coloured, moist, nutty, buttery flesh with a fresh potato taste.
Vales Emerald. Not the biggest crop. The round tubers have yellow flesh with a moist, waxy texture, new-potato flavour, and smelled earthy and buttery when cooked.
Traditional varieties of potatoes are derived from solanum tuberousum but in the last few years, “Mayan” varieties of potatoes derived from the phureja type have become available. These have a yellow flesh with a nutty flavour and creamy, dry texture. Very good for chips and roasting, but do not boil them as they go mushy. Avoid long term storage of Mayan varieties as they have a short dormancy and sprout very early. Crops are a lot smaller than traditional varieties.
Click for a quick calculation of the quantity of potatoes required to fill a piece of ground. The potato calculator is at the bottom left of the page.
Click here to go to Potato Pests and Diseases.
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