Growing potatoes in bags, from planting to tipping out

A potato bag is the easiest way to grow potatoes if you don’t have a vegetable bed. Plant two or three seed potatoes in a bag from about five weeks before your last frost, keep topping it up with compost as the shoots grow, and tip the whole thing out for new potatoes in early summer.

Bags suit early potatoes best. They’re quick, they stay compact, and the crop arrives before the bag has had a whole summer of drying out.

When to plant

Potato leaves are killed by frost, but the tubers start underground, so you can plant before your last frost. The window runs from about five weeks before your average last frost to a week after it.

Bags have one advantage over the ground here. They’re easy to move, so an early planting can sit somewhere sheltered, or come into a shed or porch, on a cold night.

Choosing potatoes

First earlies are the best choice for bags. They’re ready about ten weeks after planting, and the plants are smaller. Well-known first earlies such as Rocket and Swift do well in containers.

Second earlies and maincrop varieties will grow, but they take much longer, need more water and give big, sprawling plants. Save them for the ground.

Buy certified seed potatoes and set them in a tray, eyes up, somewhere light and cool for a few weeks before planting. Short, sturdy green shoots (called chitting) give them a head start.

Planting and filling the bag

1. Use a purpose-made potato bag or any large, sturdy container with drainage holes, about 40 litres (10 US gallons).
2. Put in about 15 cm (6 inches) of multi-purpose compost, or compost mixed with some garden soil.
3. Set two or three seed potatoes on top, shoots up, spaced out evenly.
4. Cover them with another 10 cm (4 inches) of compost and water well.
5. When the shoots are about 15 cm tall, add more compost to cover all but the top few leaves.
6. Keep doing this every week or two until the compost is a few centimetres from the rim.

Covering the stems this way is the bag version of earthing up. New potatoes form along the buried stem, and the compost keeps light off them so they don’t turn green.

Stand the bag in full sun, and avoid putting it near tomatoes, which share the same diseases.

Watering

This is where most bag crops succeed or fail. Compost in a bag dries out far faster than garden soil, and potatoes that go short of water give small, few tubers. Check every day in warm weather, and water whenever the top few centimetres feel dry. Once the plants are flowering, they need the most.

A liquid feed every couple of weeks after the bag is full helps too, as the compost runs short of nutrients.

Harvesting

First earlies are usually ready about ten weeks after planting, around when the plants flower. Push a hand down the side of the bag and feel for potatoes. If they’re the size of a hen’s egg, they’re ready.

Tip the whole bag out onto a sheet or into a barrow and pick out the potatoes. The used compost can go on the garden, but not back into a potato bag next year.

Common problems

Few or small potatoes. Almost always dry compost. Water more, and more often.

Green potatoes. Light reached the tubers. Keep them covered with compost. Don’t eat the green parts.

Blackened leaves in summer. Possibly blight, a disease of wet, warm weather. Cut off the foliage and harvest what’s there. Earlies are often lifted before blight arrives.

For potatoes in the ground, see our guide to planting potatoes in the UK, or set your own frost dates on the potato page.