Potato

Light and exposure

The potato wants sun, an open and well-lit position to develop its foliage and feed the tubers. The more light it receives, the more abundant the harvest.

Avoid the hollows where cold air pools and where late frosts strike hardest in spring. Slightly sloping or raised ground, where the air circulates, limits the risk to the young foliage in May.

Watering

The potato mainly needs water at flowering time and during tuber formation, in summer. Steady watering during this period, when the ground dries out, clearly increases the size and number of the tubers. Water copiously but spaced out rather than little and often.

Avoid wetting the foliage: moisture on the leaves encourages late blight, the main enemy under our climate. In spring, when rain is abundant here, watering is generally pointless. Stop watering as harvest approaches so the skin of the tubers forms properly.

Soil and repotting

The potato likes deep, loose, humus-rich and well-drained soil. Ground loosened deep down lets the tubers swell without constraint. It appreciates an application of well-rotted compost, but not fresh manure, which encourages diseases.

In the region’s heavy, damp soils, good soil work in spring and earthing up improve the drainage around the tubers and prevent them from rotting. Practise rotation: do not put potatoes back in the same spot for three or four years so as not to sustain soil diseases.

Temperature and humidity

The potato grows well in the relative coolness of our summers, but its foliage is very sensitive to frost. A young plant that has emerged from the ground is destroyed in a single night by a frost, even a light one.

This is the critical point of the Belgian calendar. You plant in April, but the foliage often comes up in early May, just when a late frost remains possible around Herve, before the ice saints. If a cold night is forecast while the foliage is up, earth up again to cover it with soil, or cover it with a fleece. The plant recovers if the tubers are not affected, but each frost delays the harvest.

Pruning and upkeep

The potato is not pruned, it is earthed up. Earthing up means drawing the soil into a ridge around the stems as growth proceeds, as soon as the foliage reaches about twenty centimetres, then a second time later. It is an essential gesture: it multiplies the tubers, protects them from greening in the light, and improves drainage.

Earthing up also serves as an express defence against a forecast late frost: by covering the young foliage with soil, you shelter it for the night. Remove the flowers if you wish, but it is not essential; on the other hand, never eat the small green fruits that follow flowering, they are toxic.

Pests and diseases

Late blight (Phytophthora infestans) is enemy number one under our mild, humid climate. It marks the foliage with brown spots that spread fast in a rainy summer, reaching the stems then the tubers, which rot. Choose resistant varieties, space the plants so they dry, earth up well, and cut the affected foliage without composting it at the first outbreaks.

The Colorado potato beetle (Leptinotarsa decemlineata), a yellow beetle striped with black whose red larvae devour the foliage, is the other great pest. Pick off by hand the adults, orange eggs under the leaves and larvae as soon as they appear in June. Watch out too for wireworms, those thread-like worms that bore into the tubers in recently grassed soils.

Propagation

The potato is propagated by planting tubers, called seed potatoes or seed. Buy certified healthy seed potatoes and pre-sprout them a month before planting, in light and cool conditions, so they form small, stocky, green sprouts: emergence is then quicker and the harvest earlier. Plant sprouts pointing upwards, about ten centimetres deep, every thirty to forty centimetres.

Avoid replanting your own tubers from one year to the next for more than a season or two: they accumulate viruses and diseases, and the harvest degenerates. It is better to start again from certified seed potatoes regularly to keep the crops healthy.

Toxicity

Tubers greened by light and all the green parts of the plant (leaves, stems, fruits) contain solanine, which is toxic. Never eat a green potato and keep the tubers in the dark.

Month-by-month care calendar

Green Hub tips

• Pre-sprout your seed potatoes a month before, in light and cool conditions: emergence is quicker and the harvest earlier.
• In May, keep soil ready to earth up: an express earthing up covers the young foliage if a late frost is forecast.
• As soon as an outbreak of late blight spreads, cut the foliage: the tubers keep for a few days in the ground, sheltered from contamination.
• Never eat a greened potato: light develops toxic solanine in it. Always store in the dark.