Why do my grown cucumbers taste bitter?

Last updated on October 23rd, 2023 at 08:15 pm

“Bitter is healthy” is the saying. But that doesn’t apply to vegetables that aren’t supposed to taste bitter – like cucumbers or summer squash. What went wrong there?

Why do my grown cucumbers taste bitter?
Cucumbers are almost bitter-free when properly cultivated. Especially in a greenhouse, cold frame or other uniformly warm, humid place protected from wind, they grow stress-free and do not produce the toxic cucurbitacins

Why do my grown cucumbers taste bitter?

Bitter substances are either contained in the form of tannins, for example in green tea, or are found as glucosinolates in foods. Anyone who regularly has heartburn or digestive problems should make their diet more bitter. Bitter substances ensure that the excess acid in the body’s tissues can be broken down and eliminated. The fact that bitter herbs have alkaline properties makes them doubly valuable.

But this is not true for all vegetables. In fact, caution is advised when it really shouldn’t taste bitter at all. If, for example, cucumbers taste bitter (and this also applies to other vegetables from the cucurbit family such as zucchini and pumpkin), these bitter substances, known as cucurbitacins, should be avoided. In higher concentrations, they can become dangerous to humans: After consumption, they can cause symptoms of poisoning such as diarrhea, stomach cramps, heart palpitations or headaches. If vegetables taste unusually bitter, they should therefore not be eaten!
Beware of unwanted crosses

Cucumbers were originally not as tasteless as we know them today. However, the bitter substances were bred out. Fruits from the supermarket can therefore be eaten without hesitation. All cucumber varieties commercially available today are also bitter substance-free. Many of these F1 hybrids are even higher yielding, more vigorous and flowering, and resistant to fungal and bacterial diseases. Only old varieties (conservation varieties) form bitter substances under stress.

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However, for various reasons, cucumbers from our own garden may contain too many bitter substances, cucurbitacin C, which – unlike summer squashes such as zucchini or patisson – are not lethal. Bitter they are then also only if you use self-harvested seeds from the fruits of the previous year. Due to pollination with pollen from summer squash with other cucurbits up to a kilometer away, more often the offspring from these seeds can be bitter next year, even if the fruits were in pristine condition this year. Some old varieties or cultivars of cucumbers even today carry the bitter legacy of their wild ancestors.
Avoid these cultural mistakes

Cucumbers can also become bitter due to stress, such as when the following mistakes occur during cultivation:

  • A prolonged dry spell – so always water cucumbers regularly and evenly.
  • Cold watering causes a shock when the plants are warmed by the sun, for example. It is best to always water only the soil (ideal: drip irrigation or transparent irrigation hose).
  • A too high (nitrogen-rich) or insufficient application of nutrients. Incorrect fertilizer can cause the soil to have too high a carbon content. Organic gardeners prefer organic vegetable fertilizers because they release their nutrients slowly and sustainably.
  • Cool, damp weather and sharp temperature swings, such as when hot “dog days” are followed by clear but cool nights. Outdoor cucumbers should then possibly be covered with fleece.
  • In the case of tied-up cucumbers, strong wind that constantly moves or damages the tendrils.


  • James Jones

    Meet James Jones, a passionate gardening writer whose words bloom with the wisdom of an experienced horticulturist. With a deep-rooted love for all things green, James has dedicated his life to sharing the art and science of gardening with the world. James's words have found their way into countless publications, and his gardening insights have inspired a new generation of green thumbs. His commitment to sustainability and environmental stewardship shines through in every article he crafts.

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