PotatoSolanum tuberosum

The potato wants full sun and air: a well-ventilated row dries quickly after rain, which delays blight. Avoid damp hollows and enclosed corners where the morning mist lingers. It is ideal for opening up a new plot or an old lawn, as its earthing up and dense foliage smother weeds. Keep it away from tomatoes, which share blight, and do not replant it in the same place for four years, rotation being the only real defence against Colorado beetles and nematodes. A row of broad beans or French beans alongside suits it very well.

Soil that is loose to thirty centimetres, rich in humus and on the acidic side makes the best potatoes. In autumn, spread three to four kilos of mature compost per square metre or well-rotted manure, and loosen with a broadfork. Never add fresh manure or lime in spring: they encourage scab, those corky crusts on the skin. In clay soil, growing on ridges or under a thick hay mulch, without digging, avoids compaction and makes harvesting easier. Remove stones and couch grass roots, which pierce the tubers.

Buy certified seed potatoes, 28 to 35 millimetres in size, rather than cooking potatoes, which are often treated against sprouting and carry viruses. Choose according to use: an early such as Charlotte or Nicola to eat from June, a blight-robust variety such as Sarpo Mira or Alouette for storing. Allow two and a half kilos for ten metres of row. From mid-February, set them to chit in a crate in a bright room at 10 °C: within five weeks, short purplish sprouts appear. A chitted seed potato comes up ten days earlier and stands a better chance of escaping July blight.

Plant earlies around 15 March under fleece and the other varieties from 1 to 25 April, when the soil reaches 8 to 10 °C and the lilac is about to flower; a late frost blackens the haulms but the plant grows back. Dig trenches ten to fifteen centimetres deep, seventy centimetres apart, set a seed potato every thirty-five centimetres, sprouts upwards, without breaking them, and cover with ten centimetres of fine soil. In the no-dig method, lay the seed potatoes on the soil and cover with twenty centimetres of hay: the tubers form under the mulch and are gathered by hand.

The potato grows happily in a grow bag, a large bin with holes in it or a container of at least forty litres. Put in fifteen centimetres of a compost-and-soil mix, set two or three chitted seed potatoes on it, cover with ten centimetres, then add more compost as the haulms grow, right up to the top of the container: this is earthing up in a pot. Choose an early, which is quicker, and place the container in the sun. Water regularly, as the compost dries out fast, without ever waterlogging. Expect one to two kilos per container, harvested by simply tipping the whole lot onto a tarpaulin in June or July.

Planting unchitted tubers in March in cold soil, where they rot or come up in May. Using shop-bought potatoes, which do not sprout or bring in viruses. Liming or adding fresh manure in spring, and harvesting scabby tubers. Forgetting to earth up: the potatoes turn green in the light and become toxic. Planting close together, which encourages blight and gives small tubers. Letting Colorado beetles settle in for a week without picking them off. And putting potatoes back in the same place the following year, then wondering about the poor harvests.

In Belgium, the potato usually gets by on rain. The only time water really matters is tuber formation, which begins at flowering: if the weather is dry from mid-June to mid-July, water generously once a week, fifteen to twenty litres per metre of row, at the base and in the morning. Soil that swings between drought and rain gives cracked or hollow tubers. Do not wet the haulms, as blight germinates in the droplets. Stop watering three weeks before harvesting maincrop varieties so the skins harden.

Earthing up is the key task of the crop. When the haulms reach fifteen to twenty centimetres, use a hoe to draw soil from between the rows against the stems, until only the tops of the plants show. Repeat three weeks later to form a ridge twenty-five to thirty centimetres high. This multiplies the tubers, which form on the buried stem, protects them from the light that turns them green, and buries weeds. A thick mulch of hay or straw can replace the second earthing up, keeps the soil cool and makes for a clean, easy harvest.

The autumn base dressing is enough; excess nitrogen in spring produces huge haulms and floury tubers that store badly. If the soil is poor, a handful of wood ash per metre of row at earthing up provides the potash that favours tubers. After the last earthing up, mulch the ridges with ten centimetres of straw, hay or dried grass clippings: the soil stays cool, weeds are smothered and tubers near the surface do not turn green. This thick mulch is also the best protection against cracking caused by sudden rain after a dry spell.

Blight strikes after three warm, humid days, often in early July: brown spots edged with white under the leaves. Prevent it by planting early, spacing widely, choosing resistant varieties and spraying a horsetail decoction every ten days from mid-June in stormy weather. At the first spots, cut off the affected haulms; if the attack is widespread, cut everything down to the ground and wait two weeks before harvesting. Against the Colorado beetle, collect adults and larvae every morning into a bucket of soapy water, and crush the orange eggs under the leaves. Slugs tunnel into the tubers in damp soils: harvest early.

February: setting seed potatoes to chit in crates. Mid-March: planting earlies under fleece. April: planting maincrop varieties, fleece when frost is forecast. May: emergence, first earthing up at twenty centimetres, first Colorado beetle patrol. June: second earthing up, mulching, flowering, horsetail in damp weather, harvest of earlies from the end of the month. July: daily watch for blight, watering in drought, cutting off affected haulms. August: yellowing of the haulms, watering stopped, harvest of second earlies. September: lifting maincrop varieties in dry weather, drying and sorting. October: storing in the cellar, green manure on the plot.

Earlies are harvested as needed from flowering, by slipping a hand under the mulch or lifting a plant with a garden fork, when the skin rubs off under the thumb. Maincrop varieties wait until the haulms have died back completely, two to three weeks after yellowing, so the skins harden. Lift in dry weather, pushing the fork in thirty centimetres from the plant, leave to dry on the ground for two hours, sort and bring in without washing. To spread the harvests, combine an early planted in March, a second early and a maincrop variety. A second planting of earlies in mid-July gives new potatoes for All Saints' Day.