How to grow potatoes
Which potatoes to buy
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 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:
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.
How to grow potatoes in the ground
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.
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 well-rotted manure or garden compost. 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.
Potato 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 fleece, grass clippings, straw or sacking.
As soon as the shoots emerge, cover them with earth ('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.
In a dry summer, soak the plants once a week for a couple of weeks before harvest.
How to grow potatoes in containers
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 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.
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.
If individual plants show symptoms such as yellowing or crinkled leaves or the stems turn black, this indicates a virus or blackleg disease. Remove and destroy these plants to prevent it spreading.
Check regularly for black patches on leaves and stems, especially after damp weather. This is most likely to be . Cut off all the foliage to stop the fungal spores reaching the tubers. Then leave the tubers in the ground for at least two weeks before harvesting. It's most commonly a problem on maincrop potatoes but can infect earlier potatoes as well.
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.
can also burrow into the tubers and cause similar damage to that caused by slugs. Look for shiny brown grubs. These are common on a new veg plot that was previously under grass. The problem should disappear after a couple of years.
Harvesting and storing potatoes
Early varieties will be ready when the foliage is still green. 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 the tops die down, and leave a couple of weeks for the skins to set, 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.
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.