Potato

Solanum tuberosum · spud

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At a Glance

The potato (Solanum tuberosum) is a herbaceous perennial grown in the UK as an annual crop, forming the backbone of the British vegetable garden. A member of the Solanaceae family and a close relative of tomato, pepper and aubergine, the potato produces edible tubers from underground stems known as stolons. Originating in the Andes of South America, where it has been cultivated for several thousand years, the potato reached Europe in the late sixteenth century and became established in British agriculture and allotments from the seventeenth century onwards. Today the UK grows tens of thousands of hectares of ware and seed potatoes, with main-crop, second-early and first-early types suited to a wide range of soils and climates.

A mature potato plant is upright to slightly sprawling, typically reaching 60–100 cm in height, with compound leaves and modest star-shaped flowers. Tubers form on the stolons and vary in size, shape, skin colour and flesh colour according to cultivar. Potatoes are generally grouped according to the length of their growing season, and this grouping shapes when and how they are grown in the UK.

Overview

The potato is a cool-season crop, performing best in the UK when soil temperatures are between roughly 10 °C and 18 °C. It is grown for its swollen underground stems, commonly called tubers, which are harvested from early summer (for first-earlies) through to mid autumn (for main-crops). Potatoes are versatile in the kitchen — boiled, baked, chipped, roasted or mashed — and in the garden they slot into rotation systems as a useful break crop between legumes and brassicas.

British growers divide potatoes into four broad maturity groups: first-earlies, second-earlies, main-crop, and (more loosely) salad potatoes, which may be drawn from any of the first three groups but are chosen for firm, waxy flesh. These groups dictate the planting date, the period the crop is in the ground, and its end use. Chitting — pre-sprouting seed potatoes in a cool, light place before planting — is a routine British practice that is most often used for first and second-earlies.

In the UK, potatoes are best treated as a rotation crop and grown on a four- or five-year cycle to reduce the build-up of soil-borne diseases such as potato cyst nematode and common scab.

Appearance

The potato plant produces multiple stems from each planted tuber, each stem bearing dark green, slightly rough compound leaves composed of a terminal leaflet and several pairs of lateral leaflets, with smaller leaflets between. The growth habit is bushy when young and more open by mid summer. Stems are succulent, angular in cross-section and can sprawl if not earthed up.

Flowers appear in early to mid summer and are usually white, pale lilac, pink or purple depending on cultivar, with a yellow central cone of anthers. Many varieties also produce small green or green-purple berry-like fruits, which are toxic and should not be eaten. Once flowering peaks, the tubers beneath the soil are reaching a useful size, which is why flowering time is sometimes used as a visual cue for beginning to harvest first-earlies.

The part of the plant that is eaten is the tuber — a modified underground stem with eyes (axillary buds) from which new shoots can sprout. Tuber skins range from white through cream, yellow, pink and red to deep purple, and flesh from white and cream to buttery yellow. Tuber shape varies from round to long-oval, with shallow, medium or deep eyes, all of which are characteristics used to identify and classify cultivars.

Growing Conditions

Potatoes grow well across most of the UK, including cooler northern regions and exposed sites, provided the soil is well prepared. They prefer a sunny, open position with at least six hours of direct light in summer. Light shade is tolerated but reduces yield.

Soil type matters more than soil texture. Ideal ground is a deep, fertile, slightly acidic loam with a pH of about 5.0–6.0. Very alkaline soils (pH above about 7) are associated with an increased risk of common scab, while very light sandy soils dry out too quickly to support the consistent moisture main-crop potatoes need. Heavy clay can be improved with organic matter and raised-bed cultivation, but it should not be cold and waterlogged at planting time.

Because the top growth is frost-tender, planting is timed to avoid late spring frosts damaging the emerging shoots. As a rough guide, first-earlies go in from mid to late March in southern England, a week or two later in the Midlands, and into April further north and in colder inland areas. Main-crop potatoes are planted from mid April through to mid May.

Planting and Care

Seed potatoes and chitting. Buy certified seed potatoes from a reputable supplier; using tubers from a previous crop risks introducing virus and bacterial diseases. Chitting is optional but recommended for first and second-earlies: place seed tubers in a single layer in egg boxes or trays, eyes upwards, in a cool, frost-free, light place from about six weeks before planting. Short, sturdy, greenish shoots about 2 cm long are ideal; long, pale, etiolated shoots are easily damaged at planting.

Planting. Dig a trench 10–15 cm deep, or forking individual planting holes through a bed. Space first-earlies about 30 cm apart with 45–60 cm between rows, second-earlies 35–40 cm apart, and main-crops 40–45 cm apart with 65–75 cm between rows. Place each tuber with its shoots pointing upwards and cover with soil.

Earthing up. As shoots reach about 20 cm, draw soil up around the stems to form a ridge, leaving the top few centimetres of foliage exposed. Repeat two or three times at two- to three-week intervals. Earthing up prevents shallow tubers from being exposed to light and turning green (and therefore toxic), suppresses weeds, and stabilises the plant.

Watering. Consistent moisture is the single most important factor in producing a heavy crop of well-sized tubers. Once tubers have started to form — usually around the time plants are flowering — apply about 20–25 mm of water per week during dry spells. Irregular watering leads to problems such as common scab and hollow heart, and second growth (where tubers restart growth unevenly after a dry period).

Feeding. Potatoes are hungry. Incorporate well-rotted manure or garden compost into the planting trench in the previous autumn, or apply a balanced organic fertiliser at planting. A high-potash feed, such as a tomato fertiliser, can be applied every couple of weeks once tubers begin to form. Avoid fresh manure at planting, which can encourage scab.

Pruning and training. No pruning is required. The only canopy management is earthing up, as above. Remove and destroy any plants that show severe symptoms of virus or blight to limit spread.

Propagation. Potatoes are propagated vegetatively by seed tubers. True potato seed, collected from the berries, is used in breeding programmes but produces highly variable offspring and is not used in the home or allotment garden.

Seasonal care. In summer, monitor for blight and water during dry spells. In late summer, cut down and remove the top growth of main-crop plants a few weeks before harvesting if blight is present, to limit infection of the tubers. In autumn, lift main-crops on a dry day, dry them off for an hour or two, and store only sound, undamaged tubers in hessian or paper sacks in a cool, dark, frost-free place.

Common Problems

Potato blight (Phytophthora infestans). The most damaging disease in the UK, especially in warm, wet summers. Brown-black lesions appear on the leaves, often with a pale green water-soaked margin, and a white fungal growth can be visible on the underside in humid conditions. Tubers become reddish-brown and rot. Destroy infected haulm and tubers; do not compost. Resistant cultivars are available, and earlies are usually lifted before the main blight pressure.

Common scab (Streptomyces scabies). Causes rough, corky patches on tuber skins. Worse on dry, alkaline soils. It is mainly cosmetic; flesh underneath is unaffected. Maintain even soil moisture during tuber initiation and avoid liming potato ground.

Potato cyst nematode (Globodera rostochiensis and G. pallida). A notifiable quarantine pest in the UK, with statutory controls on infested land. Symptoms are poor, patchy growth and cysts on the roots, which are just visible as small round bodies. Crop rotation and resistant cultivars are the main management tools; movement of soil and uncertified seed can spread the pest.

Blackleg and bacterial soft rot. Caused by Pectobacterium and related bacteria. Affected plants wilt, stems blacken at the base, and tubers rot into a wet, smelly mass. Remove and destroy affected plants. Avoid waterlogged soil and damage at harvest.

Virus diseases. Cause mosaic patterns, leaf distortion or stunting and reduce yield. Spread by aphids and through infected seed tubers. Buying certified seed and roguing out affected plants are the main controls.

Pests. Potato tops are also attacked by slugs, particularly in damp seasons, and by wireworm on land recently converted from grass.

Toxicity. All green parts of the potato plant — leaves, stems, flowers, and any tuber that has turned green from light exposure — contain glycoalkaloids such as solanine and are poisonous. Green tubers and any sprouted, shrivelled or bitter-tasting tubers should not be eaten. Store bought potatoes in the dark to prevent greening.

Popular Varieties

• 'Charlotte' — a popular second-early salad potato with long, oval, yellow-skinned and yellow-fleshed tubers. Waxy texture and good flavour; widely available as seed in the UK and a common choice for boiling and salads.
• 'Maris Piper' — a main-crop variety with white skin and cream flesh, long associated with UK chipping and baking. Floury rather than waxy, and a staple of British potato fields for several decades.
• 'King Edward' — a traditional main-crop with pink-blotched white skin and creamy flesh. Long considered a benchmark baking potato in the UK, though yields are modest compared with more modern cultivars.
• 'Rocket' — a very early first-early with white skin and waxy flesh, valued for its speed to crop and its performance in cooler northern parts of the UK.
• 'Desiree' — a red-skinned main-crop with yellow flesh and a smooth, fairly waxy texture. Often recommended for allotment and garden use because of its tolerance of drier conditions.
• 'Sarpo Mira' — a main-crop cultivar bred with significant resistance to late blight, with red skin and white flesh. Used in UK trials as a high-resistance option where blight pressure is severe.

Cultivars described as suitable for organic or low-input systems are listed in current AHDB / GB Potatoes resources, but specific claims vary by season and trial data, and growers are advised to check the most recent recommended lists before committing to a variety.

Pests and Diseases

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Potato in our guides

• Composting at Home: A Complete Beginner Guide for UK Gardens
• Containers for Growing Vegetables
• How to Grow Potatoes: From Chitting to Harvest
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• How to Grow Strawberries in the UK: A Complete Guide
• Summer Garden Care