When to Plant Potatoes: Soil, Timing and a Rich Harvest

Many amateur gardeners spend March and April watching the weather app: the bags of seed potatoes are ready, the neighbour has “already planted theirs ages ago” – yet uncertainty remains. A close look at the soil, weather and planting stock determines whether you end up with just a few miserable tubers or a well-stocked store cupboard.

The right time to plant potatoes: the soil matters more than the date

Dates printed on seed packets or given in gardening guides offer only broad guidance. Professionals use a different measure: soil temperature. Potatoes will only establish strongly when the ground is sufficiently warm and dry.

“A soil temperature of around 7 to 10 degrees at a depth of ten centimetres is ideal – the tubers should not go into the ground before then.”

For an exact reading, buy a soil thermometer from a garden centre. It is inexpensive and can save considerable frustration. Once it consistently reads above 10 degrees, you can begin. In many regions, this roughly means:

• Mild areas, coastal locations and the Upper Rhine: usually from late March
• Central Germany and many urban areas: often from mid-April
• Cooler locations and upland areas: more likely from early to mid-May

If you do not have a thermometer, use a simple test: sit directly on the bare soil for several minutes. If your bottom immediately feels cold, it is still too chilly for potatoes. If you can sit comfortably, planting time is approaching.

Later is better than too early: protection from cold pays off

Impatience leads many gardeners to put their tubers into freezing-cold clods of soil. They then sit in wet, cold ground for weeks, sprout reluctantly and can easily rot. Waiting a little longer usually produces markedly better results.

“It is better to wait a week than plant into frozen ground – potatoes reward patience with vigorous plants and larger tubers.”

Gardeners in cold areas, or anyone hoping for a particularly early harvest, can give the soil a helping hand. Black mulch sheeting or black plastic warms the ground by two to three degrees and can often allow planting one to two weeks earlier. Crucially, lay the covering over the prepared bed several days before planting, so that the layers beneath it have time to warm up properly.

Potato soil: loose, humus-rich and free-draining

Potatoes form their tubers beneath the soil. The looser and more airy it is, the more easily the roots can grow and the more evenly the tubers develop. A simple hand test reveals the condition of the soil: if a handful can be squeezed into a sticky, firm ball, it is too heavy and clay-rich.

Gardening professionals recommend the following for productive potato beds:

• Spread three to four centimetres of mature compost over the area in autumn
• Work in some sand where soil is very heavy to improve its texture
• Loosen the ground deeply and break up large clods
• Wait at least four years before growing potatoes in the same spot again

This break in cropping greatly reduces the risk of diseases such as blight or nematodes. Those with only a small garden can use large containers or potato-growing bags instead, giving the beds a rest.

The right tubers: why certified seed potatoes beat supermarket potatoes

Cheap eating potatoes from the supermarket are often used as an emergency substitute in the vegetable patch. Specialists advise against this. Many such tubers have been treated with sprout inhibitors, may carry diseases and frequently produce unexpectedly poor yields.

“Certified seed potatoes have been checked for health – they establish more vigorously, sprout more evenly and crop more reliably.”

Certified seed potatoes also make planning easier: around 1.5 kilograms of planting stock will yield roughly 10 to 20 kilograms of potatoes, depending on the variety and care provided. If you want an earlier harvest, give the plants a head start by chitting them, which starts the shoots before they are planted out.

Chitting potatoes: a four-to-six-week head start

To chit seed potatoes, place them in shallow trays or empty egg boxes four to six weeks before the intended planting date. Position the tubers close together but do not stack them. A bright, cool room at around ten to fifteen degrees works well, such as a north-facing windowsill or a light hallway.

• Arrange the tubers with most of their “eyes” facing upwards
• Choose a bright position, but not one in full sun
• Do not use running water or a spray bottle – the potatoes must remain dry
• Wait until the shoots are around one to two centimetres long

Chitted potatoes get going immediately once planted and produce the first new potatoes several weeks earlier than unchitted ones.

Planting day: spacing, depth and sun step by step

On planting day, the soil must not be soaking wet; it should only be slightly moist. Ideally, the plot is in full sun and can dry quickly after rain. Waterlogging in spring is disastrous for tubers.

1. Make furrows: Use a hoe or spade to create trenches ten to fifteen centimetres deep.
2. Keep the correct spacing: Leave around 30 to 35 centimetres between tubers in each row and roughly 60 to 70 centimetres between rows.
3. Position the tubers correctly: Place chitted potatoes in the furrow with their shoots pointing upwards.
4. Cover lightly: Fill the furrows with loose soil without snapping off the shoots.

The same principle works in large containers or potato-growing bags: add a layer of loose soil at the base, place the potatoes on top, then cover them with more soil. As the plants grow, gradually add more soil or loose growing medium.

Earthing up potatoes: the secret to more tubers

Once the young plants are around twenty centimetres tall, it is time for a crucial job: earthing up. Pull soil in from between the rows to form small ridges that partly cover the stems.

“Earthed-up potatoes stay in the dark, grow more reliably and often produce more and larger tubers.”

Earthing up again a few weeks later strengthens this effect. It also suppresses many weeds and prevents developing tubers from being exposed to sunlight. Potatoes that turn green at the surface develop toxic substances and should not be eaten.

Regional differences: why planting cannot always start in March

What is happening in your own garden matters far more than comparisons with friends elsewhere in the country. While potato beds in mild wine-growing regions may already be green in March, snow can still lie along the woodland edge in the Alpine foothills.

For greater certainty, observe your surroundings carefully for a year or two: when do forsythias flower, when do fruit trees come into leaf, and from when are night frosts rare? These natural signals often match the window in which potatoes begin growing reliably remarkably well.

Practical extra tips for a plentiful harvest

Alongside planting time and soil preparation, the choice of variety and ongoing care are important. Early potatoes provide tender, thin-skinned tubers for the barbecue as early as June or July. Late varieties are suitable for storage and can supply the household through winter.

Variety	Maturity group	Typical use
Annabelle	early	salads, baked potatoes
Siegfried	second early	mashed potato, purée
Bintje	late	chips, storing potatoes

Low-growing vegetables such as spinach or radishes can be planted between the rows. They make use of the space while potato plants are still small and are usually harvested before the foliage casts heavier shade across the bed. This produces a considerably greater yield from a small area.

Why crop rotation and cleanliness keep diseases away

Potatoes belong to the nightshade family, as do tomatoes and peppers. Growing these crops in the same spot year after year practically invites disease organisms in. Clear rules help prevent this:

• Leave at least four years before growing potatoes in the same bed again
• Do not plant tomatoes or peppers directly after potatoes in that spot
• Do not compost diseased foliage; dispose of it with household waste instead

This keeps the soil healthy in the long term, so plants have fewer problems with fungal disease or pests.

Extra guidance: watering, mulch and smaller risks

Potatoes need steady moisture but cannot tolerate permanently wet conditions. Extended dry periods while the tubers are forming lead to smaller harvests and can sometimes cause potatoes to split. A light organic mulch of grass clippings or chopped straw retains moisture in the soil more effectively and reduces the amount of watering needed.

Take particular care when growing in potato bags or containers: the growing medium dries out more quickly, while heavy containers can also become waterlogged. Water must always be able to drain away freely from the bottom.

The final stage is especially rewarding: carefully dig out the first new potatoes by hand or with a small digging fork, a short distance from the plant, without lifting the entire plant. The remaining tubers can then stay in the ground and continue growing. By choosing the right planting time and following these few rules, you can fill storage boxes in the cellar without stress by late summer.