Journal/Vegetable Garden · 7 min read
When to Harvest Potatoes (and How to Tell They're Ready)
By Arthur Meade · Vegetable Garden & Seasons
Flowering, dieback, skin set: the three signals that tell you when to dig new and storage potatoes — plus curing, storage and the green-potato rule.
Quick answer
New potatoes are ready roughly 50–55 days after planting, usually once the plants start to flower — sneak a hand in and feel for egg-sized tubers. Storage (maincrop) potatoes wait until the foliage has yellowed and died back; leave them in the ground about two more weeks after that so the skins set, then dig on a dry day. If the skin doesn't rub off under your thumb, it's ready to cure and store.
Potatoes are the vegetable garden's best-kept secret: the crop forms underground, invisibly, while the plant above tells you almost nothing you can't misread. Dig too early and you get marbles; dig too late into wet autumn soil and you're racing slugs and rot for your own dinner. The good news is that the plant does signal readiness — three times, in fact — and by late summer the signals are coming thick and fast. Here's how to read them.
Signal one: flowers mean new potatoes
When potato plants begin to flower — typically 50 to 55 days from planting for early varieties — tuber formation is under way beneath them. This is the moment for new potatoes: small, thin-skinned, sweet, and unlike anything from a supermarket. You don't have to sacrifice a whole plant to check. Slide a gloved hand into the soil at the side of a plant, feel for tubers of hen's-egg size, take a few, and firm the soil back so the rest keep swelling. Growers call it 'grabbling'. Not every variety flowers reliably, so treat the calendar as a backup: from about eight weeks after planting, it's worth a feel regardless.
Signal two: dieback means the crop is finished growing
For storage potatoes, ignore the flowers and watch for the opposite spectacle: sometime in late summer the foliage yellows, flops and withers away. This alarms first-time growers and delights experienced ones — dieback means the plant has finished investing in its tubers and the skins can start to thicken. From this point the potatoes are as big as they will ever get. Cut away the dead haulms (stems) if they're untidy or blighted, but resist digging the crop just yet.
Signal three: set skins mean they'll keep
Leave the tubers in the ground for roughly two more weeks after dieback. This pause is what turns a potato you must eat this week into one that stores for months: the skins toughen, minor scuffs heal, and the tuber seals itself. The test is gloriously low-tech — dig one potato and rub the skin firmly with your thumb. If skin slips or peels, wait longer; if it stays put, the crop is ready to lift and store.
How to dig them up without stabbing them
- Pick a dry day if you can — dry soil falls away cleanly and dry potatoes store far better than wet ones.
- Start the fork a good 30 cm out from the stem and work inwards, lifting the whole root zone rather than aiming for individual potatoes.
- Expect escapees: sweep through the loosened soil by hand afterwards, because every tuber you miss is a rogue potato plant next year.
- Set aside anything speared, scuffed or slug-nibbled for the kitchen this week — damaged potatoes don't store.
- Brush soil off; don't wash tubers destined for storage. Washing invites rot, and the soil film does no harm.
Curing and storing
Storage potatoes repay one last step: curing. Spread them in a single layer on newspaper or trays somewhere dark, airy and coolish — around 10–15°C — for one to two weeks. The skins harden further and small wounds heal over. Then move them into paper sacks, hessian bags or ventilated boxes in a dark spot at roughly 4–7°C: a cellar, garage or cool cupboard. Checked occasionally and kept dark, a good maincrop haul lasts six to eight months. New potatoes, by contrast, are a treat, not a pantry item — eat them within a couple of weeks.
Pro tip: if blight strikes the foliage before natural dieback, cut all the haulms off at soil level immediately and wait two to three weeks before digging. The tubers below are usually still fine, the pause still sets the skins, and removing the foliage stops blight spores washing down onto the crop as you lift it.
Warning: any potato that light has turned green has been making solanine, a bitter, toxic alkaloid — and light in storage does the same thing. Cut away small green patches generously, discard any badly greened tuber, and store the crop in genuine darkness, not just shade.
When the foliage confuses you
The awkward truth about potatoes is that the two most important diagnoses — natural dieback and late blight — both start with yellowing leaves. One means 'wait two weeks and feast'; the other means 'act today'. If your potato foliage is yellowing and you're not sure why, photograph it in PlantMe: the app identifies 500+ plant diseases with 93% top-3 accuracy, so you'll know within seconds whether you're looking at ripeness or an emergency.
Frequently asked questions
How long after flowering are potatoes ready?
New potatoes can be taken as soon as flowering starts — roughly 50–55 days from planting for earlies. For full-sized storage potatoes, keep waiting: the crop isn't finished until the foliage has died back, typically several weeks to a couple of months after flowering depending on variety.
Can I leave potatoes in the ground after the plants die?
Yes — about two extra weeks after dieback is actively good for them, because the skins set and the crop stores far longer. Beyond that, risk rises: slugs, wireworms, disease and waterlogged autumn soil all take a toll. Lift the crop once skins pass the thumb-rub test rather than leaving it indefinitely.
Why are my potatoes so small?
Usually one of three things: they were dug too early (tubers do most of their swelling in the final weeks), the plants were stressed by drought during tuber formation, or too much nitrogen pushed leafy growth at the expense of the crop. Water consistently from flowering onwards and hold your nerve until dieback.
Is it safe to eat potatoes that have sprouted?
A firm potato with small sprouts is fine once you've snapped the sprouts off and cut away the eyes generously — the sprouts themselves, like green skin, are high in glycoalkaloids such as solanine. A soft, wrinkled, heavily sprouted potato belongs in the compost, not the pan.
Try it yourself
Diagnose it instantly with PlantMe
Snap a photo of any plant or leaf. Get the species, the diagnosis, and a care plan in seconds.
Download on theApp Store