Potatoes Institut de Beauvais

Planting

Potatoes need light, deep, and rich soil. Choose a sunny location. Add well-rotted compost in the previous autumn, by hoeing it into the soil to a depth of 5cm (2in), after loosening the soil. Planting takes place under shelter in February-March for early varieties. For other varieties, plant them from mid-March to May, depending on the climate. Wait until the soil is at least 10°C (50°F). The flowering of lilac is often a sign to start planting. Plant several varieties in your vegetable garden for a varied menu.

Loosen the soil deeply and form rows 10cm (4in) deep, spaced 70cm (28in) apart. Place the tubers, sprout upwards, every 40cm (16in) (or 30cm (12in) for early varieties). Cover with fine soil. When the plants reach 15cm (6in), mound up by bringing fine soil to the base of the stems, to a height of 20cm (8in). Mounding up encourages tuber formation and water drainage. You can mound them up again a month later. Mulch the base of the plants with successive thin layers of grass clippings mixed, if possible, with dead leaves. This protection keeps the soil moist and limits weeding.

Potato cultivation does not require watering, except in case of high temperatures. In this case, water the base without wetting the foliage to prevent the appearance of fungal diseases.

Diseases and pests

Potatoes are susceptible, like tomatoes, to late blight. This is a fungal disease caused by the fungus Phytophthora infestans. Late blight develops in warm and humid weather. Small spots appear, which are white underneath the leaves and brown on top. As a preventive measure, here are some tips to limit the risk of late blight:

• do not grow several plants of the Solanaceae family (such as potatoes, tomatoes, aubergine, peppers, and chili peppers) in adjacent rows, as they are susceptible to the same diseases

• in terms of rotation, wait 4 years before growing a Solanaceae plant in the same location

• space the plants, both within and between rows, to encourage air circulation and prevent rapid disease spread

• if you need to water, do not wet the foliage

• spray preparations such as horsetail decoction or garlic purin

Harvesting can also be hindered by the Colorado potato beetle, an insect of the Coleoptera order. You will recognise it by its yellow head and its yellow and black striped body. The best solution, although a bit time-consuming, is to remove them as they appear. As a preventive measure, sow blue flax seeds between your rows of potatoes. Sow from April to June in shallow furrows. Besides its repellent effect against Colorado potato beetles, flax will brighten up the vegetable garden with its pretty little blue flowers. You can also interplant peas between your rows of potatoes.

Other planting methods

The detailed planting method above is the most common. Other methods exist, such as mulch planting and tower planting.

Mulch planting involves placing the tubers on the ground and covering them with a layer of mulch. This protection is supplemented as the plant grows, with the tubers always being kept away from light.

Tower planting or bag planting is practical for small spaces but requires regular watering. The tower can be built from various materials (wood, wire mesh, tyres). The tubers are placed on a bed of potting soil or compost. As the plant grows, it is covered with more potting soil, leaving only the topmost leaves exposed, until reaching the top of the tower, letting the tubers form throughout the height of the container. Harvesting is done when the foliage has dried up.