How to grow potatoes and best varieties

Potatoes are such a versatile vegetable, from new potatoes with their unique flavour to maincrops that can store all winter and be used for all sorts of dishes, from mash to chips.

The Which? Gardening experts share their tips for growing potatoes, plus our Best Buy varieties.

How to grow potatoes: month by month

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Best potato varieties

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Full testing results for potatoes

New potatoes (first earlies)

Salad potatoes (second earlies)

Blight-resistant potatoes

Potatoes for growing in pots

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Types of potatoes

Although any potato will grow and produce a crop, even sprouting ones from the back of the larder, it's best to buy 'seed potatoes' from a garden centre or by mail order. When Which? Gardening magazine compared growing seed potatoes with ones from the supermarket, we found that supermarket potatoes aren't worth growing. They sprout poorly, there's less choice of variety, the variety you want won't necessarily be available at the right time, you'll get a lower yield and poorer quality, there may be disease problems and it's not necessarily cheaper.

Seed potatoes are traditionally sold by weight. A 1kg bag will provide at least 10 tubers - fine for an allotment but too many for a small garden. Look for garden centres that sell small quantities or individual tubers.

Varieties are usually divided into categories according to the speed they produce edible potatoes:

First early potatoes are the quickest to crop and are usually dug fresh and eaten before the skins harden. These are referred to as 'new potatoes' in late June and July.

Second early potatoes are next, from July into August, and include the waxy 'salad potatoes'. Dig these up as required through the summer.

Maincrop potatoes are usually left in the ground until the tops die off and the tubers' skins have set in late summer/early autumn. Dig them up in one go and store them for winter use. Early maincrops will not store much beyond Christmas, so use these first. Late maincrops will take you into spring.

When to plant

Chitting

Unpack seed potatoes as soon as you get them and lay them out on a tray somewhere cool and light. This is known as 'chitting'. Doing it will mean the seed potatoes will grow plump, green sprouts and be ready to grow when you plant them out. Tubers kept in the dark produce long white sprouts that are easily damaged.

Growing in the ground

Grow potatoes on a different patch of ground each year, over a cycle of three, or preferably four, years. This 'crop rotation' helps to stop any pests or diseases building up. Potatoes are greedy crops (ie they take up lots of nutrients) and growing them involves disturbing the soil - it makes sense to spread this around the veg plot.

Grow early potatoes in rows 40cm apart and maincrops in rows 60-75cm apart. This makes digging the crop easier and means you can earth up the base of the plants in one go.

Plant early varieties in late March in mild areas, or early April in cold areas, followed by second earlies and maincrops during April. Space the tubers 40cm apart.

Potatoes will benefit from a generous amount of soil improver. Work this into a trench or spread on the soil surface.

Dig a trench about 25cm deep and 30cm wide. This is especially worthwhile on light soil because you can incorporate some organic matter at the same time.

You don't have to plant potatoes in a trench, but do plant them at least 15cm deep. Remember the new tubers form on the stems above the seed tuber. Use a trowel or an old-fashioned potato planter.

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Growing in pots or potato bags

You can grow potatoes in pots, special potato bags or even an old dustbin as long as it has drainage holes. Fill the container with a Best Buy compost for containers with some controlled-release fertiliser until it is about a quarter full. Bury one chitted seed potato near the bottom.

As soon as the potato shoots grow, keep adding more compost until the container is full. Keep the compost moist, but not too wet - if you don't water enough your crop will be small.

Discover our Best Buy watering cans

To check whether the potatoes are ready to harvest, reach into the compost and feel around. The potatoes are ready when they're the size of an egg.

How to grow big potatoes for baking

Large, evenly sized potatoes are perfect for jacket potatoes. When Which? Gardening magazine looked at the best way to grow this sort of potatoes, we found that the secret is to feed with a general fertiliser, such as Growmore - a 'potato feed' gave poorer results. It's also important to water your plants, especially in dry weather.

Try a Best Buy garden hose

Caring for your plants

Protecting from frost

Potato leaves and stems are very sensitive to frost. If a frost is predicted (and a ground frost may occur if the overnight forecast is below 5C), cover the plants with a double layer of horticultural fleece, grass clippings, straw or sacking.

Keep your plants safe with a Best Buy frost-protective cover

Earthing up

As soon as the shoots emerge, cover them with soil ('earthing up'). This will help increase the number of tubers, stop them turning green, and protect them from frost. Cover them with more earth until there's a ridge around the plants. Alternatively you can use soil improver.

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Watering

Watering is needed when you see flowers, but only if conditions are dry. Water about twice a week and give a decent amount. Stop watering when the leaves are showing more than about 10% yellowing, as plants mature.

How and when to harvest

Early varieties will be ready when the foliage just begins to turn yellow. Sometimes, but not always, the tubers will be ready when the plants flower. If in doubt, feel under the plants for egg-sized tubers. 

For maincrop varieties, wait until roughly a third of the leaves are yellow and then lift the crop on a dry day. Work along the row, pushing a fork in from one side and push under the centre of the plants. Take some time to remove all the tubers, not matter how tiny, or they'll grow next year and disrupt that year's crops.

Storing

Early varieties should be eaten straight away but maincrops can be stored for later use. Lay them in a dark place to dry off completely before storing. Remove any that area rotting (especially if blight affected the foliage), damaged or have slug or wireworm holes. These won't keep, so eat them first, once you have cut out the damaged areas. Store the good tubers in hessian or paper bags (sometimes fish and chip shops will give these away). Tip them out every couple of weeks to check over the tubers and remove any that are starting to rot.  

Common growing problems

Blight

Potato blight or 'late blight' is a devastating fungus disease that spreads rapidly in wet weather. Like a mildew disease, to which it is related, it attacks the foliage, but can get washed down to damage the tubers.

The first signs are small, dark spots, often on the edges of leaves. If the weather is wet, a white mould surrounds these spots, usually on the underside of the leaf. This shows that spores are being produced. The spots grow, covering the whole leaf. They also spread onto stems. Infected tubers have brown and purple skin blotches that go into the flesh of the tuber. The flesh is brown/red and granular. Infected tubers may shrivel and dry, but are often infected by rotting organisms and liquefy in storage, smelling strongly and contaminating other tubers.

Cutting off infected foliage can prevent spores from reaching the tubers. Leave at least two weeks between removing the foliage and lifting the tubers, so viable spores lurking on the soil surface don’t contaminate the tubers as you lift them. Store the tubers in dry, cool conditions to reduce the disease’s activity and subsequent rotting. Check potatoes every month; get rid of rotting ones.

Following recent research by the James Hutton Institute, blight alerts for potato and tomato growers are now being issued under the Hutton Criteria, which has replaced the Smith Period. The minimum temperature needed by the disease, 10°C over two consecutive days, is unchanged, but it's now known that relative humidity only needs to be above 90% for six hours on both consecutive days for the disease to spread, rather than 11 hours, as previously thought. In these conditions, the disease spreads rapidly. In hot, dry weather it temporarily 'dries up', but breaks out again if conditions become favourable. This typically happens during early summer in the west and late summer in the east.

To avoid potato blight, dig out as many tubers as you can when you gather the potatoes. At the end of the season, remove all potato tubers, even tiny ones, and destroy them. Digging over the plot so frost can kill any remaining tubers will help. Throw away, burn or bury deeply any leftover or rotting tubers from storage, so they can’t grow the following year. Protect new crops by earthing up well. A layer of soil will protect tubers from spores falling from infected foliage.

Potato blight persists on living material so you can safely compost the stems and leaves as they are dead, provided the temperature in the compost is high enough, such as in a Hotbin. If you're using an open compost bin it's unlikely to get hot enough to destroy the blight spores, so it's best to burn affected plants or put them in the council green waste bin as their composting facilities run at higher temperatures. There is a possibility that blight spores could overwinter on other plant material but this hasn't been tested scientifically yet. Don't compost the tubers as they are alive and will carry the blight spores; put these in your council green-waste bin.

Frost damage

Leaves that have been frosted will suddenly develop brown, dead patches. This is most common earlier in the year when frost is more likely. Your plants should recover. To help prevent it happening, cover the leaves with earth or compost (earthing up) or put on horticultural fleece on cold nights.

Slugs

Slugs can damage the tubers underground, especially on maincrop potatoes in late summer/early autumn. If you suspect this might be a problem, don't wait until you dig up the tubers. The best solution is to treat the area with a biological control such as Nemaslug as this will reach slugs underground.

Read more about slugs and snails

Wireworm

Wireworms feed on the roots of young plants in the spring and summer. Seedlings of root vegetables in particular wilt and die, due to loss of roots. The damage can be seen as small, dark wounds on the stems of affected plants.Vegetables such as French beans, lettuce, onions, strawberries and other garden plants are also affected. Beans, chrysanthemums and tomatoes may have tunnelled stems; this is how the wireworm travels up from the soil inside the plant. Widely spaced plants can suffer disproportionately as the wireworms concentrate their attack on the nearest available plants. The first sign you will see is the sudden wilting and collapse of plants. Exploring the soil round the plant will reveal the culprit. They also tunnel into potatoes. Dark, narrow mines disfigure the inside of potatoes, making them unusable. You don’t see this attack until you lift the crop, only to find it damaged beyond rescue. Cutworms and especially slugs also attack potatoes, but these two usually make large cavities. In some cases, millipede attacks follow the cutworms, slugs and wireworms, but they are not the primary cause of damage.

Grassland is the wireworms' favourite habitat. Fortunately, they don’t seem to do much damage to the grass. If you have lawn troubles, suspect leatherjackets or chafer grubs. However, if you dig wireworm-infested turf and turn it into a garden, you are likely to run into problems. For the first year or two the wireworms feed on the buried grass, but when that runs out, they will attack garden plants. Weedy, run-down gardens and allotments are also more likely to suffer attacks. Naturally moist or irrigated soils are most at risk. Sandy soils don't suit them, they are too dry.

Check potatoes in September for signs of damage. If they have been attacked, lift and store the tubers. There are no chemical controls. 

Blackleg

When blackleg is present, potato-plant leaves are small and yellowed, and may be distorted. The stem base shows distinct blackening and then dies back. The vascular stands are blackened so cutting the stem across reveals black 'dots'. The 'mother tuber' rots completely and if the bacterium strikes early, the plant may be killed and will not crop. Wet soils tend to exacerbate the problem, which is usually introduced on a symptomless seed potato, often via wounds.

Remove affected plants as soon as you see them. Lift crops in dry weather and only store potato tubers that appear to be in perfect health.

You can help prevent it by buying seed potatoes rather than saving your own. Grow them in a new site every year to avoid 'volunteer' potatoes which may be infected. Improve drainage if your soil is wet. Choose resistant varieties such as 'Charlotte' and 'Vales Sovereign'. 

Common scab

Dry soils and dry summers are a favourite of scab.  It produces corky irregular wide and flat bumps, often in groups. These are frequently pitted and covered in scabs. Stems are also attacked, but not noticeably. 

Once the crop is affected there is no cure for this disease. The tubers may look unappetising but they are still edible if peeled. Storage is not affected.

Avoid common scab by not using lime before planting potatoes. Use plenty of soil improver when preparing the soil. Water during dry spells and grow resistant varieties. 'Accent', 'Anya', 'Pentland Crown', 'Golden Wonder', 'Nadine' and 'Wilja' are relatively resistant, but 'Desirée' and 'Maris Piper' are very prone to attack.

Don't worry if some of the seed potatoes you buy have a bit of scab on them. Scab is legally permitted in seed potatoes in the UK, as it does not pass to the following generation. Make sure you buy certified seed potatoes as these will have passed regulatory inspections to ensure acceptable levels of any problems.

Powdery scab

You'll notice raised irregular scabs which release a powder of spores. This powder is brown and the spores can survive for as long as 10 years in the soil. Before the scabs burst, there may be surrounding areas of discoloured skin. In extreme cases cankers form, disfiguring the tubers with large outgrowths. These aren't spreading and cauliflower-like, as in wart disease. Another feature of powdery scab is the tumour-like growths which form on the roots.

It's associated with heavy soils and wet seasons, but if potatoes are overwatered, it can occur in any summer and on light soils. The spores germinate in the soil and release swimming spores that affect roots by travelling in the soil moisture. More spores are released from these roots; they enter tubers through natural openings such as lenticels and wounds. Here, new scabs are produced. If there's a dry spell followed by wet weather, cankers and tumours are produced. Spores from these cankers then attack newly formed tuber tissues, making more scabs.

Unfortunately there’s no cure. Spores are long-lived so don’t grow potatoes on infected sites for at least three years.

Avoid manure from places where potatoes are fed to animals and reject affected or damaged seed. Look for resistant varieties, such as 'Sante'.

Black scurf

Black scurf is a fungal disease which damages early potato shoots in cold, wet soils. Look out for black speckles, which can be scraped off the tubers. Earlier in the season, watch out for brown stem bases; these infected areas may go right around the stem. The leaves become rolled and wilted. A white powdery collar can sometimes be seen around the stem at ground level, too. In severe cases, where they are planted in cold soils, the young sprouts are killed and the crop does not survive.

It is carried on the seed, or is already present in the soil. It is most likely to occur when the conditions are cool and on light soils.

The spots don't look good, but the potato beneath is sound and can be cooked as usual. Losses are from extra peeling, not reduced yield. Sprout potato seed indoors and delay sowing until the soil is warm; mid-April should be fine. As an extra insurance, a fleece covering will warm the crop up. Try not to grow potatoes on the same spot of ground more often than once in three years.

Internal rust spot

With this problem, the potato tubers look perfectly normal from the outside, but when cut open the flesh within is peppered with small rusty coloured spots. The tubers can still be eaten, although you’ll need to cut out the infected parts. 

Internal rust spot may occur on a wide range of soils, but is most common on those that are light or have a low organic matter content. Inadequate supplies of lime and potassium make internal rust spot more likely. To help avoid it occurring, improve the soil's organic matter content by mulching with or digging in soil improver and consider applying lime well in advance of planting if the soil is extremely acidic. Keep the crop adequately supplied with water. Both 'King Edward' and 'Arran Consul' varieties appear to show resistance to internal rust spot.

Growth cracks

These are when the tubers have deep cracks that have healed over with a rough, callus-like covering, this is a sign that the tuber has grown very fast when wet weather followed dry. In these conditions, the tubers stop growing, then have a spurt of growth when it rains. Viruses can occasionally cause cracks as well, but soil-moisture changes are the main cause. This problem makes the tubers harder to clean or peel, but they are perfectly edible.

Try not to let potatoes dry out completely. Water heavily in dry periods, especially if your soil is prone to drying out. Adding soil improver may help your soil hold moisture, but watering is the only sure way to limit growth cracks

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Hollow heart

The potato tubers appear perfectly normal on the outside and are often quite large, but when cut open there are one or more cavities within. The cavities may vary in shape but are often star-shaped and show dark discolouration. The tubers can still be eaten, although you’ll need to cut out the infected parts before you cook them.

Rapid potato tuber growth encourages hollow heart and the symptoms often occur when the weather has been dry and the crop is then irrigated. An over-wet soil or an over-dry soil may also encourage it, as may the excessive use of fertilisers.

To avoid it occurring, keep the soil just moist at all times and avoid erratic watering or excessive fertiliser use. 

Jobs to grow potatoes throughout the year

How we test potatoes

We grow lots of varieties alongside each other and a sample of each variety grown is cooked and assessed for taste. They are then individually tasted by a group of trained assessors, who describe the appearance, smell, flavour and texture of each variety of potato and give them an overall score.