How do I grow potatoes?

Potatoes are among the easiest and most productive things to grow, and the one technique that matters is earthing up. Tubers form along the buried stem, so the more stem you bury as it grows, the more you harvest. Light reaching a tuber turns it green and inedible, which is the other reason it matters.

Safety

What you'll need

• Seed potatoes
• Egg boxes for chitting
• Spade
• Potato growing bags (optional)
• Compost or well-rotted manure

Step by step

1. Buy certified seed potatoes rather than using supermarket ones.Seed stock is certified free of the main diseases. Supermarket potatoes are often treated to suppress sprouting.
2. Chit them: stand them eyes-up in egg boxes somewhere cool and light for 4–6 weeks.You want short, stubby green shoots. Long pale shoots mean it's too dark or too warm.
3. Plant once the worst frost risk has passed — typically March for earlies, April for maincrop.Potato foliage is frost-tender. If a late frost threatens after they emerge, cover them or earth up over the shoots.
4. Plant 15cm deep, 30cm apart for earlies and 40cm for maincrop.Rows about 60–75cm apart. In bags, three seed potatoes to a large bag is plenty.
5. Earth up when the shoots reach about 20cm — draw soil up around them, leaving the tips showing.This is the key step. Tubers form on the buried stem, so earthing up directly increases the crop.
6. Repeat earthing up every few weeks as they grow.Two or three times over the season. In bags, add compost rather than soil.
7. Water consistently, especially once flowering starts.Tuber formation coincides with flowering, and that's when water shortage most reduces the crop.
8. Harvest earlies about 10 weeks after planting, when the flowers open.Rummage under one plant to check size before lifting the lot.
9. For maincrop, wait until the foliage yellows and dies back, then leave two weeks before lifting.That fortnight lets the skins set, which is what allows them to store rather than rot.

Tips

• Growing bags work well on a patio and make harvesting trivial — tip the bag out rather than digging.
• First earlies are the best use of limited space: they're quick, they crop before blight season, and new potatoes are the biggest improvement over shop-bought.
• Never compost potato foliage affected by blight, and don't replant potatoes in the same ground for three or four years.
• Store maincrop potatoes in the dark in paper or hessian sacks, somewhere cool but frost-free. Light turns them green.

Common mistakes

• Not earthing up — Tubers form on the buried stem. Without earthing up you get a fraction of the potential crop and green tubers.
• Using supermarket potatoes as seed — They may carry disease and are often treated to suppress sprouting.
• Harvesting maincrop immediately after the foliage dies — The skins haven't set, so they damage easily and won't store.
• Eating green potatoes — Green indicates solanine, which is toxic. Cut away small green areas or discard the potato.

Questions people ask