When to plant potatoes

Potatoes go in once the soil has warmed to about 43–46°F. In the UK and in mild parts of Central Europe, first earlies can be planted from late March, second earlies in the first half of April and maincrops from mid-April to early May. In colder areas of Germany, Austria and Switzerland, plant earlies in April and the rest from mid-April into early May.

The tubers themselves sit safely underground, but the leaves are killed by frost. If a cold night is forecast after the shoots have come up, draw soil over them or cover the row with fleece or straw overnight. That is why many German gardeners plant later varieties only around the Eisheiligen in mid-May.

Chitting gives you a head start. About four to six weeks before planting, from around February, stand the seed potatoes in egg boxes or trays with the end that has the most eyes facing up, somewhere light, cool and frost-free at around 50–59°F. Plant them when they have short, sturdy shoots about 0.4–0.8 in long. Long, pale shoots are a sign the spot was too dark.

Buy seed potatoes from a garden centre or seed supplier. They are certified free of the main diseases, which matters because potatoes carry viruses and blight from one year to the next in the tuber.

Pick a sunny spot with loose, deep soil and plenty of organic matter. Potatoes are hungry plants, so dig in well-rotted compost or manure beforehand, about 3 litres per square metre. Don't lime the bed before potatoes: alkaline soil encourages scab. Slightly acidic soil around pH 5.5–6.5 suits them best.

Set each tuber shoots up, about 4–6 in deep. Rows are easiest: take out a trench or single holes, lay the tubers in, and cover them gently so you don't snap the sprouts. UK guides go to the full 6 in; German advice often plants a little shallower and relies on earthing up.

Space first and second earlies 12 in apart in rows 24 in apart. Maincrops grow bigger and need 14–16 in in the row and 28–30 in between rows. A 120 × 80 cm raised bed fits two rows of four earlies, eight plants, or six maincrops. Earlies suit a raised bed best because they are out before blight usually strikes and leave room for a second crop.

Earth up once the shoots are about 6–8 in tall: draw soil from between the rows up around the stems so only the top few leaves show. Repeat two or three times, every two to three weeks, until the ridge is about 8–12 in high or the leaves meet across the rows. Earthing up keeps light off the tubers so they don't turn green, protects young shoots from late frost and smothers weeds. It isn't thought to add much yield, so no-dig gardeners can skip it as long as the tubers stay covered.

Water matters most once the plants start forming tubers, roughly from flowering until about three weeks after. Dry soil then gives fewer, smaller potatoes and makes common scab much more likely. In dry spells, water deeply rather than a little and often.

With compost dug in at planting, most soils need nothing more. On poor soil, a nitrogen-rich organic feed at the second earthing up helps maincrops.

First earlies are ready from June into July, roughly three months after planting. A good sign is when the plants flower or the flower buds drop, though not every variety flowers. Scrape back a little soil first: if the tubers are the size of a hen's egg, start digging. New potatoes don't keep, so lift them as you need them.

Second earlies follow in July and August. Maincrops are ready from late August into October. For storing, wait until the foliage has died back, then cut it off and leave the tubers in the ground for another two to three weeks so the skins firm up. Don't leave them much longer in a wet autumn, when slugs start tunnelling in.

Lift on a dry day with a fork pushed in well away from the plant. Let the potatoes dry on the surface for a couple of hours, brush off loose soil but don't wash them, and set damaged ones aside to eat first.

Store them dark, cool and frost-free, ideally at 39–43°F, in paper or hessian sacks or slatted crates. Colder than that and they turn sweet; warmer and they sprout. Light turns them green, and green patches contain solanine: cut them out generously, and throw away tubers that are very green or heavily sprouted.

Potatoes are grouped by how long they take. UK catalogues say first earlies, second earlies and maincrop; German ones use Reifegruppen from very early to late. Very early varieties need about 90–110 days, late ones 140–160.

Earlies give tender new potatoes in early summer, take up less room and usually escape blight. Maincrops take the bed all season but give the biggest harvest and the potatoes that store through winter.

If blight hits your garden most summers, look for resistant varieties. The RHS names the Sarpo varieties such as 'Sarpo Mira' and 'Sarpo Axona', as well as 'Carolus' and 'Alouette'. Old favourites like 'King Edward' are very susceptible.

Late blight is the big one. In warm, wet weather, brown patches spread across the leaves within days and the plants collapse; the tubers then rot with reddish-brown marks under the skin. It usually arrives from June. Chitting and growing earlies helps you harvest before it takes hold. Once about a quarter of the leaves are affected, cut all the foliage off at ground level and wait about two weeks before lifting so the skins can harden. Don't compost blighted foliage, and keep tomatoes well away from potatoes: they catch the same disease.

Common scab leaves rough, corky patches on the skin. It is mostly cosmetic: peel and eat. Keep the soil moist while tubers form and don't lime before potatoes.

In Germany, Austria and Switzerland, the Colorado potato beetle arrives in spring. Check the plants often, shake off and collect the striped beetles, and crush the orange-red egg clusters under the leaves. Ladybird eggs look similar but are yellower, so leave those. In the UK the beetle is a notifiable pest: report any sighting to the Animal and Plant Health Agency.

Potatoes belong to the nightshade family, with tomatoes, peppers and aubergines. Leave at least four years before potatoes return to the same bed, and don't follow them with other nightshades. This keeps potato cyst nematodes and soil-borne diseases from building up.

Planting tables often put potatoes next to bush beans, spinach, marigolds or nasturtiums and warn against sunflowers, cucumbers and squash. We found no solid evidence for these pairings; they are tradition.

The one rule with a real reason: keep potatoes and tomatoes apart, in space and in the rotation, because blight spreads easily from one to the other.