When to plant potatoes, earth them up and harvest them

Plant your potatoes when the soil reaches 8 °C, not on a fixed date. In Belgium and Luxembourg, that generally falls from mid-April to mid-May. Chitted seed potatoes go in from mid-March in soil that has already warmed. After that, the plant gives the signal. You earth up when it is about twenty centimetres tall. You harvest by its flowers and its foliage.

When to plant: soil temperature decides

The variety catalogue of the Luxembourg Ministry of Agriculture says it in one line. Plant from mid-April to mid-May, from 8 °C of soil temperature. Chitted seed potatoes can go in from mid-March, in a warmed soil that has drained. A drained soil has lost its excess water.

Even in good conditions, emergence takes time. In the Belgian trials of the Sarpira variety, the comparison varieties took 31.5 days on average to come up. This is counted from planting until half the plants have emerged.

Frost matters too, but later. The shoots coming out of the ground fear spring frosts. The RHS, the British horticultural society, advises covering them for the night if frost is forecast. A cloche, hessian, straw or simply soil are enough.

Chit to gain a few weeks

Chitting means getting short, strong sprouts to grow before planting. The Luxembourg catalogue advises it for earlies, dry soils and vegetable-garden growing. Its method comes down to four steps.

1. Lay the tubers in trays or egg boxes, in three layers at most.
2. Leave them for a day or two at 15 to 20 °C to wake them up.
3. Then keep them for three to four weeks at 10 to 12 °C, in natural light.
4. Aim for stocky, coloured sprouts of 1 to 2 cm.

The RHS starts in late January in mild regions, up to early March in the coldest. It counts four to six weeks and lets the sprouts reach about 5 cm. Both methods rely on light, which gives short, green sprouts rather than long, white ones. Chitting your potatoes puts a figure on the gain from the trials.

How to plant

The RHS digs a trench 15 cm deep and sets the seed potatoes sprouts up. Spacing depends on the type of variety.

The RHS gives no spacing of its own for second earlies. Start from the one for first earlies. For a small area, the Luxembourg catalogue counts 3 to 4 tubers per square metre in the vegetable garden.

With no garden, a container at least 30 cm wide and deep is enough, with one seed potato per 30 cm of diameter (RHS). The step-by-step is in Potatoes in a bag or a tower.

Earth up when the plant is about twenty centimetres tall

Earthing up means drawing soil up around the base of the stems to form a ridge. The tubers then stay out of the light. Exposed, they turn green and load up with solanine, a bitter substance. The longer the light lasts, the more they accumulate (University of Alaska Fairbanks). The RHS throws away green potatoes at harvest.

Farmers do the same, on their scale. In the CRA-W trial at Gembloux in 2025, planting took place on 28 April and the final ridges were formed on 9 May. Earthing up also serves as weeding. At Gembloux, the next two passes, on 15 and 28 May, weeded the ridges. The detail is in Earthing up your potatoes.

In dry weather, the RHS waters. For a maincrop variety on poor soil, it adds a nitrogen-rich organic fertiliser around the second earthing up.

When to harvest: watch the plant

First earlies

The RHS harvests them in June and July in the UK, sometimes as early as 12 weeks after planting. Wait until the flowers open or the buds drop, with tubers the size of a hen's egg. Feel under one plant with your fingertips before lifting the whole row.

Maincrop varieties

They are harvested from late August to October. If they are healthy, they can stay in the ground until mid-autumn (RHS). To make them keep, follow these steps.

1. When the leaves turn yellow, cut all the haulm and remove it.
2. Wait 10 days, so the skin of the tubers hardens.
3. Lift with a fork pushed in at least 30 cm from the plant, so as not to hurt them.
4. Let them dry for a few hours in the sun, then brush off the soil.

Then keep only intact, dry tubers, in a cool, dry, dark, frost-free place. Check them every few weeks. The RHS advises having eaten them before the start of spring. Harvesting and storing your potatoes covers the cellar, the clamp and the storage moves.

And blight?

Potato blight is the same organism as on the tomato. It strikes in summer. In 2025, a rather dry year in Wallonia, the first blight appeared on 24 July on the Bintje in the Gembloux trial. On 14 August, half the foliage of the Agria variety was destroyed.

When blight hits the foliage, the RHS says you can generally still harvest and eat the crop if you act fast. These tubers do not keep. Potato blight gives the moves specific to the potato. For the tomato, read Tomato blight.

The choice of variety matters a lot. The CRA-W bred Sarpira, scored 8.3 out of 9 for blight resistance in 2021, in a trial with no treatment. Blight-tolerant potatoes compares the varieties tested in Wallonia.

The app calculates the planting date for you, set to the weather in your garden. Start here.

FAQ

When to plant potatoes in Belgium?

When the soil reaches 8 °C, generally from mid-April to mid-May. Chitted seed potatoes can go in from mid-March if the soil is warmed and drained.

Should you chit potatoes?

It is not compulsory. The Luxembourg catalogue advises it for earlies, dry soils and the vegetable garden. Count three to six weeks in the light, out of the frost.

How high to earth up?

Start when the stems are about 23 cm tall, letting only 10 cm show. Repeat until you have a ridge of 20 to 30 cm (RHS).

When to harvest new potatoes?

When the flowers open or the buds drop. The tubers are then the size of a hen's egg. Feel under one plant to check.

Why cut the haulm before harvesting?

So the skin hardens. The RHS cuts the haulm when it yellows, waits 10 days, then lifts. The tubers keep better.

Photo: Markus Spiske, Unsplash

Sources

1. Ministère de l'Agriculture du Luxembourg, Commission des variétés, Catalogue des variétés de pommes de terre 2025 (plantation de mi-avril à mi-mai à partir de 8 °C de température du sol, dès mi-mars pour des plants prégermés, profondeur, butte, densité au potager, prégermination)
2. RHS (Royal Horticultural Society), Potatoes: grow your own (prégermination, dates selon le type, écartements, buttage, gel, récolte, conservation)
3. CRA-W, Fiwap et Biowallonie, Pommes de terre robustes en agriculture biologique : essai variétal 2025, rapport scientifique (Gembloux : plantation le 28 avril, buttes le 9 mai, récolte le 15 septembre, premier mildiou le 24 juillet)
4. University of Alaska Fairbanks, Cooperative Extension Service, Green potatoes: causes and concerns (verdissement à la lumière, solanine, buttage, stockage au noir)
5. Pleinchamp et CRA-W, Sarpira, la nouvelle variété de pomme de terre développée au CRA-W (13 avril 2023 : levée et fermeture des lignes en jours après plantation, note de mildiou)