Solanum tuberosum
Family: Solanaceae

One of the most important food crops in the world, and the staple food of temperate climates, the potato is produced in nearly every country. Cultivated in Central and South America as long as 4000 years ago, and introduced to Europe by the Spanish conquistadores in the 16th century, it took some 200 years to become a popular food in Europe. At the beginning of the 20th century, there were more than 1000 known varieties, while today fewer than 100 varieties are in cultivation. However, there has been renewed interest in recent years in many of the more unusual cultivars, and so more of these are becoming available to home gardeners. These are all varieties of Solanum tuberosum, the low-growing perennial, cultivated for its starchy, edible tubers (the swollen ends of underground rhizomes). The potato is grown throughout the UK and Ireland. Filling and quite nutritious, it is a versatile vegetable which can be served boiled, mashed, fried, baked or layered with cream or yoghurt, and cooked in curries, soups and stews.

Cultivation

Propagate by planting 'seed potatoes', using the small, whole tubers or pieces obtained by cutting the tuber into sections, each with one or two buds (eyes). Tubers can be selected from an existing crop or from purchased potatoes, but it is much better to buy certified seed potatoes, as these are guaranteed to be disease-free. (True potato seed, which forms inside the fleshy green or purple fruits, resembling tiny tomatoes, is used only for breeding.)

Next, the seed tubers are encouraged to form sturdy shoots before planting, a process known as chitting or sprouting. In late winter spread the tubers out on trays, with the 'eyes' facing upwards, and keep them in a cool, frost-free place with good light. When shoots are 2.5 cm (1 in) long, the tubers can be planted. Chitting takes about six weeks.

Planting is carried out in spring, starting in early spring with the early cultivars. These are followed by second-early potatoes, then finally the main-crop cultivars. Plant tubers 10-12 cm (4-5 in) deep and 35 cm (14 in) apart, in rows spaced 45 cm (18 in) apart. Maincrop cultivars are planted 75 cm (30 in) apart in rows spaced 80 cm (32 in) apart. This allows access for weeding, feeding and earthing up. Shoots should emerge within three to four weeks. At this stage, they are very frost-tender.

Use a well-drained soil that is slightly acid and contains some organic matter. When plants are about 25 cm (10 in) high, they should be earthed up, in other words the soil should be mounded on each side of the plant. This helps smother weeds, and, more importantly, prevents the tubers from turning green. Potatoes need a plentiful supply of nutrients and regular watering if the weather is dry. Complete fertilizer can be laid in bands alongside the rows.

Harvesting can begin as plants die down, but new potatoes can be dug from about four weeks after flowering. These must be used quickly as they do not store well. Green colouring on potatoes is poisonous and unplanted seed pieces should be destroyed or buried deeply and not fed to live-stock.

Pests that may attack potatoes include potato cyst, eelworm, wireworms, cutworms and slugs. Among the diseases that may be encountered is potato blight. This is a serious and frequent, fungal disease that is worse in warm, humid conditions. Common scab is another frequent disease, most troublesome if the soil is alkaline. Copious watering deters it. It is best not to grow potatoes on the same piece of ground more than once in every four years, to prevent a build up of soil-borne pests and diseases. Crop rotation is therefore advisable.

Climate

Zone 10, but grown as an annual, summer crop in all climates.