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Do you know why the potato you buy does not sprout?

A lifted potato is still alive, and the only thing it knows how to do as the months pass is sprout. The one you buy in August has gone since spring without doing it, and that does not happen on its own.

Cold is not the way out

The first thing you think is that keeping it cold is enough. It is not: the European rule itself pushes the other way. When the store drops below a certain temperature the starch in the tuber turns into sugars, and those sugars are what darken the potato when it is fried.

That is why Regulation (EU) 2017/2158, the one that sets out what companies making crisps and chips have to do, writes in its Annex I that «the temperature shall be appropriate to the potato variety stored and it shall be above 6 °C», and that «during storage the level of reducing sugars in potatoes shall be tested».

A few lines further down, the same annex settles the problem it has just created: «sprouting shall be suppressed in long term stored potatoes where permitted, using appropriate agents». Storing warm and not sprouting are incompatible things in a living potato, so a product goes in between the two. On table potatoes no law demands it, but the chain asks for it all the same: a sack with sprouts does not sell.

The product that did that job ceased to exist in 2020

For decades the job was done by a single active substance, chlorpropham, known in the trade by its initials, CIPC. It was fogged into the store and the potato held for months without waking up.

The Commission did not renew its approval. Implementing Regulation (EU) 2019/989, of 17 June 2019, required Member States to withdraw the authorisations of products containing it by 8 January 2020 at the latest, and set that any grace period for using up stocks should expire by 8 October 2020 at the very latest.

That can be checked today in a minute. In the Spanish Ministry's Register of Plant Protection Products, the five Spanish products containing chlorpropham —Altair, Altair Plus, Cryptic, Fruitfog-CIPC and Germidorm C— are still in the database, and all five carry the status «Cancelado», cancelled.

Six years on, chlorpropham still turns up

Here is the part almost nobody tells. The substance was banned, but it did not leave: it stayed stuck to the walls, the floors and the ventilation of sheds that took it in every winter for thirty years. A potato that has never been treated comes out of the store with traces on it.

The European Union has put that in writing in the driest place available, the residue limits table: «monitoring data show that there may be a contamination of potatoes above the default MRL of 0.01 mg/kg when stored in facilities with a history of chlorpropham use».

Out of that comes a temporary limit that steps down as the stores are cleaned: 0.4 mg/kg from 2 September 2021, 0.35 from 14 September 2023 and 0.2 from 6 January 2026, with the next review tied to the data submitted by 16 June 2027. That number is set to tell the inheritance of an old shed apart from the illegal use of a withdrawn product.

0.4Sept 20210.35Sept 20230.2Jan 2026mg/kgdashed line: 0.01, the default MRL
The temporary limit for chlorpropham in potatoes, as the regulations listed at the foot stepped it down.

What is applied today: in the field and inside the shed

The Ministry's register is searched by crop and by substance. In the field, before lifting, maleic hydrazide is sprayed on the leaf (Super Stop Brot 60, no. 22147; Super-Stop-Brot 18, ES-00703): a treatment «in the open air by foliar spraying», done while the plant is still green, months before the potato reaches any store.

Inside the store there are four authorised routes, and all four are applied as a fog or a gas, never onto the potato already in the sack:

That last name has already come up here: it is the same gas that decides the yellow of a banana, and Annex I of Implementing Regulation (EU) 2021/1165 allows it in the strictest certified production in the Union with a condition written in one line, «only for bananas and potatoes». The same molecule ripens a fruit and puts a tuber to sleep, depending on how and when it is used: it is told in what happens to a banana.

Fieldmaleic hydrazideLiftingthe crop endsStore+6 °C · foggingShop«de conservación»
Where each treatment enters: one on the leaf, months earlier; the other in the air of the shed.

What the label says, and what is optional

The potato has its own rule in Spain: Royal Decree 31/2009. It requires the pack to carry who packed it, the nature of the product —«Patatas de primor» (earlies), «Patatas nuevas» (new potatoes) or «Patatas de conservación», stored potatoes—, the name of the variety, the country of origin, the category, the net weight, the batch and the size grade.

Look at what is not on that list. The lifting date appears nowhere, nor the months in store. And the treatment has a line of its own, in the section that opens with the word that changes everything: «Optionally: recommended culinary use, skin colour, flesh colour, tuber shape, particular production circumstances, relative storage and keeping conditions, an indication of whether or not it has been treated with anti-sprouting products» — our translation of the Spanish text, which is the only official one.

In other words: the one fact that would answer the question in this page's title may be printed or left off. Out of the whole sack, the clue that is compulsory is those two words, «de conservación»: they do not say how long, but they say it has been kept.

It is not wrong. It is done badly some of the time

Without a store there is no potato in June, and a shed that works clean and treats only as much as it needs is doing its job well. A shed washed out properly is not the one still dragging thirty-year-old chlorpropham, and that difference does not show on the skin of the potato nor has to be written anywhere.

Four questions settle it, and none of them is aggressive: where it is from, when it was lifted, how long it has been in store and whether it carries a sprout suppressant. On a supermarket shelf they have no answer.

At a farm they do. 103 farms on this list publish their phone number, and the questions that work are written out in what to ask. And almost everybody has a potato grower nearby: among the 150 farms on this list there is someone lifting it close to your house.

Carry on here

Sources: Regulation (EU) 2017/2158 — Annex I: store temperature «above 6 °C», testing of reducing sugars and suppression of sprouting in long-term storage (2026-08-16) · Implementing Regulation (EU) 2019/989 — non-renewal of chlorpropham: authorisations withdrawn by 8 January 2020, grace period expiring by 8 October 2020 (2026-08-16) · Regulation (EU) 2021/155 — temporary MRL for chlorpropham in potatoes of 0.4 mg/kg, applying from 2 September 2021, with the note on facilities with a history of use (2026-08-16) · Regulation (EU) 2023/377 — the same temporary MRL cut to 0.35 mg/kg, applying from 14 September 2023 (2026-08-16) · Regulation (EU) 2025/1163 — the temporary MRL cut to 0.2 mg/kg, applying from 6 January 2026; review with the data submitted by 16 June 2027 (2026-08-16) · Register of Plant Protection Products (Spanish Ministry of Agriculture, Fisheries and Food) — products and statuses cited; database updated 14 August 2026 (in Spanish) (2026-08-16) · Royal Decree 31/2009 — commercial quality standard for table potatoes: compulsory marking and the optional mention of anti-sprouting treatment (in Spanish) (2026-08-16) · Implementing Regulation (EU) 2021/1165 — Annex I: ethylene, «only for bananas and potatoes» (2026-08-16)

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