There is something quietly satisfying about lifting your own potatoes, and you do not need a vegetable plot to do it. A decent-sized bag, a sunny corner of the patio and a bag of multi-purpose compost will get you a surprisingly generous crop. I have grown spuds in bags on a cramped paved yard for years, and the method is forgiving, tidy and easy to fit around a busy week.

Why grow potatoes in bags?

Bags suit small spaces because they lift the whole operation above the ground. You can tuck them against a warm south-facing wall, move them out of the way when you want the patio back, and avoid the backache that comes with digging a trench. Drainage is easy to control and there are no slugs hiding in the soil from last year.

Yields are better than most people expect. A well-tended 40-litre bag planted with three seed potatoes will typically give you somewhere between 2kg and 3kg of tubers — enough for several meals, plus a few precious new potatoes eaten within an hour of lifting.

Choosing and chitting your seed potatoes

Start with proper seed potatoes rather than supermarket ones, which are often treated to stop them sprouting. Buy them in late January or February and look for:

• First earlies such as 'Rocket', 'Swift' or 'Pentland Javelin' — fast, reliable and perfect for bags.
• Second earlies such as 'Charlotte' or 'Kestrel' — a little slower but excellent flavour and storage.
• Salad or speciality types if you fancy something different, though these are less forgiving in a bag.

Stand the tubers upright in an egg box, rose end (the end with the most eyes) pointing upwards, in a cool, bright, frost-free spot. Within four to six weeks you want short, sturdy shoots about 1–2cm long. A dark, warm cupboard gives long, pale, useless sprouts, so keep them near a window in an unheated room.

Planting into the bag

Use a purpose-made potato bag or a heavy-duty compost sack with plenty of holes punched in the base and lower sides. Sit it on pot feet or a couple of bricks so water drains freely and the base does not sit in a puddle.

Add about 10–15cm of multi-purpose compost, then space three chitted tubers evenly across the surface, shoots pointing up. Cover them with another 10cm of compost and water gently until it settles. Position the bag in full sun, sheltered from strong wind, and keep the compost just moist while you wait for shoots to appear — usually two to four weeks.

Earthing up as shoots grow

This is the step that separates a decent crop from a disappointing one. As the shoots reach about 15–20cm tall, add more compost around them, leaving roughly 5cm of leafy growth showing above the surface. Repeat this earthing up two or three times as the plants grow, until the bag is nearly full.

• Burying the stems encourages more tubers to form along them.
• It also stops any potatoes near the surface turning green, which makes them bitter and unsafe to eat.
• If a late frost is forecast, drape fleece over the bag overnight and remove it in the morning.

Watering and feeding

Bags dry out far faster than open ground, especially once the foliage is thick. Check the top 5cm of compost with your finger daily in warm weather and water thoroughly until it runs out of the drainage holes. Little and often is worse than a good soak every day or two, because it encourages shallow roots and weak plants.

Once the plants start flowering, give them a weekly feed with a high-potash tomato fertiliser to push energy into the tubers rather than the leaves. Keep watering consistently — a drought followed by a soaking can cause splitting and hollow centres, and it also makes the crop more prone to common scab.

Harvesting and planning a second crop

First earlies are usually ready around 10–12 weeks after planting, when the flowers have dropped and the foliage is just beginning to fade. You can steal a few new potatoes earlier by carefully feeling around in the compost with your fingers — a technique gardeners cheerfully call furtling — but leave the rest to size up.

For maincrops, wait until the foliage yellows and dies back, then stop watering for a fortnight so the skins firm up. Tip the bag onto a sheet of polythene, sort out the tubers, and let them dry somewhere cool and dark for a few hours before storing. Spent compost can be spread on borders or reused for a late salad crop.

And if you fancy potatoes with Christmas dinner, plant a couple of second-cropping tubers in fresh compost in late July or early August, keep the bags in a warm spot and move them under cover before the first hard frost. There is no better way to finish the growing year than lifting your own spuds in December.