Bitter squash: should you be worried?
In short: a squash, pumpkin or courgette that tastes clearly bitter must not be eaten, even cooked: the bitterness comes from cucurbitacins, irritant substances that cooking does not destroy. The risk mainly concerns garden squash grown from saved seed or sprouting by itself on the compost heap, but sometimes shop-bought squash too. The right reflex: taste a small raw piece and spit it out if it is bitter. Ornamental gourds are never for eating.
Every autumn, gardeners ask the same question: can you eat that fine pumpkin that grew by itself on the compost heap? And every autumn, poison centres remind us that some squashes make people ill. Between rumour and real danger, here is what we know, what is exaggerated, and the simple steps that are enough to avoid poisoning.
Why some squashes are bitter
Wild squashes are naturally bitter. They produce cucurbitacins, substances which, according to the French food safety agency ANSES, help them repel the insects that eat them, such as caterpillars. Cucurbitacins are very bitter and very irritating to the digestive tract.
Over the centuries, the varieties we eat (pumpkins, red kuri squash, butternuts, courgettes, pattypans) have been selected to be mild, almost free of cucurbitacins. But bitterness has not disappeared from the squash gene pool: it can reappear after a cross. The German Federal Institute for Risk Assessment (BfR) points out that cucurbitacin levels depend on the variety but also on growing conditions.
A key point: cucurbitacins survive cooking. A soup or gratin made with a bitter squash remains toxic.
What is the real risk?
The risk is real, but it needs to be kept in proportion.
| Where | What was observed | Source |
|---|---|---|
| Belgium | 37 calls and 43 people poisoned by squash in 2018 | Belgian Poison Centre, quoted by La DH (2019) |
| France | 353 people with symptoms between 2012 and 2016, no life-threatening cases, 4% of moderate severity | Poison centres, quoted by ANSES |
| France | Squash from the family vegetable garden in 54% of cases, bought in a shop in 46% | ANSES |
| Germany | A 79-year-old man died in 2015 after eating a dish of bitter home-grown courgettes | BfR, German press |
Symptoms appear soon after the meal, and a small amount is enough, the Belgian Poison Centre points out: vomiting, intestinal cramps, sometimes bloody diarrhoea that can lead to dehydration, as well as dizziness, heavy salivation and palpitations. Children and people who are poor at detecting bitterness are most at risk.
The German case remains exceptional: the BfR notes that, in general, the bitter taste prevents people from swallowing a dangerous amount. Provided they don't ignore it.
Compost-heap squash
This is the most common case in the garden. A seed from last year germinates in the compost, the plant grows with astonishing vigour and bears fine fruit. Is it safe to eat?
Xavier Mathias, a former organic market gardener, trainer and author of a French book on squashes and cucurbits, explains in a recent video that these squashes often come from seeds produced by a cross, with another variety in the garden or the neighbour's. The result is unpredictable: a lucky draw or an unlucky one. He has eaten some very good ones, but has also come across squashes so bitter that you could not swallow a spoonful.
ANSES is more cautious: it recommends not eating squashes that have come up by themselves in the garden, and not resowing seed from your own harvest, buying new seed each time you sow. The Belgian Poison Centre gives the same advice.
This year's cross does not poison this year's fruit
This is the most widespread myth, and it is wrong. If you grow courgettes next to ornamental gourds, this season's courgettes do not become bitter as a result.
The reason is botanical. The fruit develops from the ovary of the female flower, which is already there before pollination: it is tissue of the mother plant, which keeps its own characteristics. Foreign pollen only changes the seeds inside the fruit. Iowa State University's extension service sums it up: a cross between two varieties of the same species does not show in the first year; you discover the result when you sow the seed, and it is sometimes inedible.
Another useful detail: crosses only happen within the same species. Courgettes, pattypans, Halloween pumpkins and most ornamental gourds all belong to Cucurbita pepo and can cross with one another. Butternuts (Cucurbita moschata) and winter pumpkins or red kuri squash (Cucurbita maxima) are different species.
Colocynth: the false and the true
The French word coloquinte covers two very different plants.
Ornamental gourds sold in autumn, in fanciful shapes and colours, are mostly Cucurbita pepo squashes, the same species as the courgette. Xavier Mathias suggests calling them "false colocynths". Selected for their looks rather than their flavour, they remain rich in cucurbitacins. ANSES considers them all toxic: they are for decoration, never for cooking. Check the label, as they are sometimes found on the fruit and vegetable shelves.
True colocynth (Citrullus colocynthis) is a relative of the watermelon, from the dry regions of the Mediterranean, Africa and Asia. It bears small round, extremely bitter fruits, long used as a purgative. The medical literature describes haemorrhagic colitis after eating it, and high doses can be fatal. You won't come across it in Belgian gardens, but it circulates as a traditional remedy.
True or false: myths about bitter squash
| Myth | Verdict |
|---|---|
| "Cooking removes the bitterness and the danger." | False. Cucurbitacins survive cooking. |
| "My courgettes have become toxic because my neighbour grows ornamental gourds." | False for this year. The cross only affects the seeds, so next year's plants if you resow them. |
| "A squash that sprouted on the compost is bound to be toxic." | False, but the risk is real: the result of a cross is unpredictable. Health authorities advise against eating them. |
| "Shop-bought squash is never bitter." | False. In France, 46% of poisonings with a known origin involved a bought squash. |
| "A bitter squash can be recognised by its look or smell." | False. According to ANSES, it looks exactly like an edible squash. At home, taste is the only reliable test. |
| "A little bitterness doesn't matter if you only eat a bit." | Don't try it. The BfR treats an unusually bitter taste as a warning sign: spit it out and throw it away. |
The right steps
Before cooking a squash, pumpkin or courgette, especially one from the garden:
- Taste a very small raw piece. An edible squash tastes neutral or slightly sweet.
- If it is bitter, spit it out and throw away the whole squash. Don't try to "rescue" it by cooking it or mixing it with other vegetables.
- Don't resow the seeds of your squashes: buy new seed.
- Don't eat squashes that came up by themselves, on the compost or elsewhere.
- Keep ornamental gourds for decoration, away from the squashes you cook.
- Take a photo of the squash before preparing it and keep some of the dish: if someone feels unwell, this helps identify the cause.
Other garden plants can be deceptive too: see our article on datura, and our Christmas plant myths for holly, mistletoe and poinsettia.
Sources
ANSES. (2019, 31 October). Attention aux courges amères ! French Agency for Food, Environmental and Occupational Health & Safety. https://www.anses.fr/fr/content/attention-aux-courges-ameres
ANSES. (2024, 15 October). Cette année encore, attention aux courges amères ! https://www.anses.fr/fr/content/cette-annee-encore-attention-aux-courges-ameres
Bibliothèque nationale de France. (n.d.). Mathias, Xavier (1970-....) [Authority record]. BnF catalogue. https://catalogue.bnf.fr/ark:/12148/cb140348653
Bundesinstitut für Risikobewertung. (2015a, 4 September). Caution when eating bitter-tasting courgettes (zucchini) [BfR Communication No. 027/2015]. https://www.bfr.bund.de/cm/349/caution-when-eating-bitter-tasting-courgettes.pdf
Bundesinstitut für Risikobewertung. (2015b, 4 September). Vorsicht beim Verzehr von bitteren Zucchini [Mitteilung Nr. 027/2015, full version]. https://www.bfr.bund.de/cm/343/vorsicht-beim-verzehr-von-bitteren-zucchini.pdf
Der Standard. (2015). Tödliche Zucchini. https://derstandard.at/2000021020598/Toedliche-Zucchini
Goldfain, D., Lavergne, A., Galian, A., Chauveinc, L., & Prudhomme, F. (1989). Peculiar acute toxic colitis after ingestion of colocynth: a clinicopathological study of three cases. Gut, 30(10), 1412-1418. https://doi.org/10.1136/gut.30.10.1412
Iowa State University Extension. (n.d.). Cross-pollination between vine crops. Yard and Garden. https://yardandgarden.extension.iastate.edu/how-to/cross-pollination-between-vine-crops
Jimenez, L. (2019, 31 October). Halloween : gare à l'intoxication aux courges amères, voici les techniques pour les repérer. La DH. https://www.dhnet.be/actu/belgique/2019/10/31/halloween-gare-a-lintoxication-aux-courges-ameres-voici-les-techniques-pour-les-reperer-EZUXH6R6QBBATGETSL7IQC3J6I/
Khan, S. A., Shelleh, H. H., Bhat, A. R., & Bhat, K. S. (2003). Colocynth toxicity: a possible cause of bloody diarrhea. Saudi Medical Journal, 24(8), 904-906. https://doi.org/10.15537/1658-3175.2140
Mathias, X. [Xavier Mathias]. (2026, 25 October). Courges toxiques ? [Video]. YouTube. https://www.youtube.com/watch?v=i5Knm_h1WfU