Oliver Pemberton
There is something deeply satisfying about pulling your own potatoes from a bag on the patio. No garden? No problem. A sunny corner, a sturdy sack, and a few seed potatoes are all you need to grow a crop that tastes far better than anything from the supermarket. Growing in bags gives you complete control over soil, water, and pests, and it means you can move your crop to catch the sun or dodge the frost. Whether you have a tiny courtyard or a large allotment, bags and containers earn their place.
Why bags and containers work so well
Potatoes are forgiving plants, but they hate two things: waterlogged roots and competition from weeds. Growing them in bags solves both. You can mix a light, free-draining compost that warms up quickly in spring, and you can water precisely without drowning neighbouring plants. Bags also let you escape the worst of soil-borne diseases such as eelworm, because you start with fresh growing medium each year. If blight strikes, you can move infected bags away from healthy ones. For anyone with limited space, containers turn a paved patio into a productive plot. Children love the magic of tipping out a bag and finding buried treasure.
Choosing your bag, container and compost
Purpose-made potato bags are usually 40 to 50 litres and about 35cm deep. That is the minimum size for a decent crop. You can also use sturdy woven sacks, builder's buckets, or old compost bags turned inside out. Whatever you choose, make sure it has drainage holes at the bottom and sides. Clear plastic is best avoided because light encourages green, toxic tubers and algae. A layer of gravel or broken crocks at the base helps water escape.
For compost, use a peat-free multipurpose mix with added loam or John Innes No. 2. This holds moisture without becoming soggy. Do not use garden soil straight from the border: it compacts in bags, drains poorly, and may carry disease. Mix in a handful of slow-release potato fertiliser or a few scoops of well-rotted manure. Fill the bag to about 15cm from the base to begin with.
Chitting and planting your seed potatoes
Buy certified seed potatoes from a garden centre or specialist grower. Supermarket spuds are often treated to stop them sprouting and may carry disease. Around six weeks before planting, stand them in a cool, bright, frost-free place with the rose end (the end with most eyes) facing up. Egg boxes are perfect. Short, sturdy green shoots are what you want; long, pale ones mean the light is too weak.
Timing depends on variety. First earlies can be planted in late February under cover, or late March outdoors. Maincrops go in from late March to mid-April. Plant two or three tubers per 40-litre bag, spaced evenly and with the shoots facing upwards. Cover with 10–15cm of compost and water gently. Keep the bag somewhere sheltered from hard frost; a cold greenhouse or a sunny porch is ideal until the risk passes.
Earthing up, watering and feeding
When shoots reach 15–20cm tall, add more compost to bury the stems, leaving just the top leaves showing. This is called earthing up, and it is the secret to a heavy crop. The buried stems produce extra tubers, and it stops any potatoes near the surface turning green. Repeat every two to three weeks until the bag is full.
Water little and often. Potatoes in bags dry out fast, especially on windy days. Aim to keep the compost moist but never sodden. In hot weather you may need to water daily. From the moment flowers appear, feed weekly with a high-potash tomato feed to swell the tubers. Stop feeding once the foliage starts to yellow.
- Never let the bag dry out completely – this causes hollow heart and cracked tubers.
- Avoid overhead watering in the evening – wet leaves encourage blight.
- Mulch the surface with grass clippings or compost to conserve moisture.
Pests, diseases and troubleshooting
The main threats are slugs, aphids and blight. Slugs love young shoots and hollow out tubers. Keep bags off the ground on pot feet or bricks, and go out with a torch after rain to remove them by hand. Aphids can spread viruses; a strong jet of water or a few ladybirds usually keeps them in check. Blight shows as brown patches on leaves that spread quickly in warm, humid weather. If you spot it, cut off all foliage immediately and wait three weeks before harvesting, so spores do not wash down to the tubers.
Yellowing leaves in early summer often mean hunger or waterlogging. Check drainage and give a liquid seaweed tonic. If tubers are small and plentiful, the plants needed more water during flowering. If they are large but few, you probably planted too few tubers or did not earth up enough.
Harvesting and enjoying your spuds
For new potatoes, harvest when plants are flowering, about 10–12 weeks after planting. Furtle gently with your fingers and take a few eggs from the sides, leaving the plant to grow on. For a full harvest, wait until the foliage turns yellow and dies back. Stop watering for two weeks to let the skins set. Then tip the bag onto a tarpaulin and rummage through the compost with your hands – a fork risks spearing the crop.
Eat any damaged tubers first. For storage, let clean, undamaged potatoes dry in a cool, dark place for a few hours, then pack them in paper sacks or cardboard boxes. Keep them in a frost-free shed or garage. Home-grown potatoes rarely last as long as shop-bought ones, but that is no hardship when they taste this good. Boil them with mint, roast them in goose fat, or simply steam and butter them. You will wonder why you ever grew anything else.
