When to Plant Potatoes: An Expert Explains What Matters

Missing the right moment to plant potatoes can cost you kilo after kilo of crop – an expert explains what matters.

As soon as the days begin to lengthen, many amateur gardeners cannot wait to get planting potatoes into the ground so that the store cupboard is full by late summer. Yet the information printed on the seed-potato bag, advice from neighbours and assorted lunar calendars can quickly become confusing. The answer is not a fixed date: it is the combination of soil temperature, weather conditions and well-prepared seed potatoes.

The ideal time to plant potatoes: let the soil, not the calendar, decide

Many gardeners rigidly follow a date in March or April, but this is often wrong. Potatoes are sensitive to cold, wet ground. Planting too early can lead to rot or weak plants; planting too late can mean missing the opportunity for truly early tubers.

“What matters is how warm the soil is at a depth of ten centimetres – not what the calendar says.”

Garden experts advise planting potatoes only when:

• the soil temperature is consistently at least 7 to 10 degrees,
• severe late frosts are no longer expected,
• the soil is no longer saturated and heavy.

A soil thermometer from a garden centre is inexpensive and can prevent poor decisions. If it reads above 10 degrees at planting depth for several consecutive days, the season can begin. Covering the ground with black plastic or dark fleece can often bring planting forward by one to two weeks, as the soil warms more rapidly.

The simple sitting test: using your own sense of temperature

Anyone without a thermometer can rely on a very traditional indicator: their own sense of warmth. Sit on the bare soil for a few minutes. If you do not immediately feel cold and it seems cool rather than icy, conditions are usually suitable for the tubers too.

The planting window varies considerably by location:

• Coastal areas and mild western locations: often from late March
• Central areas and many river valleys: usually from mid-April
• Cooler upland areas and hills: often only from early to mid-May

A practical rule of thumb is to plant a week later rather than start in “concrete-like soil”. Potatoes usually make up a delay of a few days with ease when they are planted into pleasantly warm, airy ground.

Preparing soil for potatoes

Potatoes thrive in loose, deep soil. This allows the tubers to expand without becoming misshapen or rotting. Heavy, compacted ground makes growing them unnecessarily difficult.

“The more easily the soil crumbles in your hands, the more comfortable the tubers will be.”

Here is a quick check: take a handful of soil and squeeze it. If it forms a hard, sticky lump, it contains too much clay and loam, and is either still too wet or naturally too heavy. If the ball falls apart easily, the texture is suitable.

To make the soil more potato-friendly in the long term, it helps to take action in autumn:

• spread 3 to 4 centimetres of mature compost over the area,
• work in a little sand where the soil is heavy,
• loosen large clods with a digging fork rather than over-cultivating the soil.

It is also worth considering crop rotation. Potatoes should not return to the same plot for at least four years. This reduces pressure from diseases such as potato blight and tuber blight, as well as nematodes, which are tiny threadworms living in the soil.

Healthy seed potatoes: where the harvest begins

Even the best planting date is of little use if the starting material is poor. Supermarket potatoes are usually treated with sprout inhibitors and are unsuitable as seed potatoes. Specialist suppliers offer certified seed potatoes that have been inspected and checked for disease.

“Around one and a half kilos of healthy seed potatoes can produce 10 to 20 kilos of eating potatoes – quality plays a part.”

Those wanting an early crop can “chit” the tubers in good time. This gives the plants a small head start for the season.

Chitting potatoes for an early harvest

Around four to six weeks before the intended planting date, place the seed potatoes in shallow trays or egg boxes. The tubers should be:

• arranged in a single layer,
• kept somewhere bright and cool, at around 10 to 15 degrees,
• protected from strong direct sunshine.

After a few weeks, sturdy, short shoots measuring one to two centimetres will appear. These compact sprouts are ideal. Long, thin “windowsill shoots”, on the other hand, snap easily and weaken the plant.

Potato planting day: a step-by-step guide

A sunny site matters on planting day. Potatoes need light and warmth, but do not tolerate waterlogging. In heavy soil, slightly raised ridges or beds help excess water drain away more quickly.

• Measure the planting spacing: Mark rows around 60 to 70 centimetres apart, leaving 30 to 35 centimetres between tubers within each row.
• Make the furrows: Use a hoe or spade to create grooves roughly 10 to 12 centimetres deep.
• Place the tubers: Position the shoots upwards and avoid damaging them where possible. Handle chitted potatoes especially carefully.
• Cover the potatoes: Replace the soil so the tubers sit around 5 to 10 centimetres beneath the surface.

If you only have a balcony or small courtyard, potatoes can also be grown successfully in large containers or sturdy bags. The important points are at least 30 to 40 litres of compost volume per plant and drainage holes to allow surplus water to escape.

Earthing up: the overlooked yield booster

Once the plants reach around 15 to 20 centimetres tall, it is time for an important task: earthing up. Use a hoe to draw soil up around the stems, creating a small ridge.

“Earthed-up potatoes produce more tubers, stay in the dark more effectively and are less likely to turn green.”

A second pass is generally needed after two to three weeks. The same principle applies in a pot on the balcony: keep adding compost so that only the top part of the plant remains above the growing medium. In this way, the container gradually “grows” upwards.

Common mistakes – and how to avoid them

Many reductions in harvest are caused not by pests but by minor oversights. Common examples include:

• Soil that is too wet: Tubers rot before they can sprout. Better: wait for a drier spell and ensure good drainage.
• Untreated supermarket seed potatoes: These carry a higher risk of disease. Use certified seed potatoes instead.
• No crop rotation: Growing potatoes in the same spot year after year weakens the crop.
• Planting too shallowly without earthing up: Tubers turn green and become inedible.

What soil temperature and drainage actually mean

When gardeners refer to soil temperature, they do not mean the air temperature, but the temperature at the depth where the tubers sit. It changes far more slowly than the air: after cold nights, the soil can still be icy in the morning even when the sun is already warming the garden.

Drainage is the soil’s ability to take in water and release it again. Well-drained soil retains moisture without turning into a puddle. Sand and compost improve this quality, while soils made up purely of clay often hold water for too long.

Why the effort is genuinely worthwhile

Following a few clear rules pays off: planting into sufficiently warm, loose soil produces strong plants with deep-reaching roots. They cope better with dry spells and use nutrients more efficiently. This makes the crop more resilient, even during weather extremes.

Potatoes also leave room for creative experimentation: mixed planting with dwarf beans around the edge, flowering strips to deter pests, or trying different varieties – from an early waxy tuber for summer salad to a floury variety for Sunday mash. Anyone who keeps the right planting time and the basics in mind can continue learning through play year after year – while filling the store cupboard with home-grown potatoes.