Advanced options
Chit seed potatoes (sprout them in egg boxes on a windowsill, 4-6 weeks before planting): earlies go in March-April, harvest June-July before blight season even starts: the container grower's cheat code. Earth up (or top up the bag) as shoots grow: buried stem = more potatoes. The economics are honest: potatoes are cheap to buy, so grow earlies for the flavour of just-dug new potatoes: the one version money genuinely can't match.
What The Potato Yield Calculator Works Out
- You need: containers x seed potatoes per container, which is three for the standard 40-litre grow bag. Certified seed potatoes cost about 30p to 50p each and buy virus-freedom over supermarket sprouters for pennies.
- Expected harvest: plants x the yield per plant for the type. First earlies return around 0.8 kg of new potatoes per plant, second earlies 1.1 kg and maincrop 1.5 kg or more where space and season allow, so four bags of earlies give 9 kg to 10 kg from a fiver of seed.
- The honest verdict: supermarket potatoes are so cheap that the harvest's shop value barely doubles the seed cost. The case for growing rests on the June early dug an hour before dinner, a flavour the supply chain cannot ship because sugars turn to starch from the moment of lifting.
- Seed potatoes per container and custom yield (advanced): three per 40-litre bag is standard; a 30-litre bucket takes two and a dustbin five. Override the yield with your own record, since a well-watered, earthed-up bag can beat the averages and a dry July can halve them.
- Compost needed (advanced): containers x litres each, rounded up to 40-litre bags. Compost is the real cost of container potatoes: four bags need 160 litres, about GBP 24 of multipurpose compost bought fresh, so the card lets you halve it for a second season or zero it for reused compost.
- Total outlay (advanced): seed plus compost plus any one-off spend on grow bags or containers (GBP 2 to GBP 5 per reusable bag).
- Cost per kg grown (advanced): the total outlay divided by the harvest, set against the shop price. It is usually dearer than supermarket maincrop and cheaper than premium salad potatoes at GBP 2 to GBP 3 a kilo.
- Saving versus the shop (advanced): shop value minus the outlay. A negative figure is normal in year one with fresh compost and new bags; it turns positive once compost is reused and the bags are paid for.
- Portions (advanced): the harvest divided by your portion size, with 200 g per person a typical serving, expressed as family meals for four. Earlies do not store, so plan to eat them within two or three weeks of lifting.