Bitter cucumbers: toxicity, possible reasons & fixes

Nothing is more disappointing than discovering that your homegrown cucumbers, which you have lovingly nurtured, are bitter. Cucumbers can taste bitter for a variety of reasons, which we will go over and teach you how to fix your cucumbers so that they taste great.

Cucumbers (Cucumis sativus), especially those grown at home, should taste fresh, light and even slightly sweet. However, issues with pollination and stressed cucumber plants can cause the fruits, or part of them, to taste too bitter.

Why do cucumbers taste bitter?

Cucumbers, like courgettes (Cucurbita pepo) and squash (Cucurbita), are members of the cucurbit plant family (Cucurbitaceae), which all contain some extremely bitter cucurbitacin compounds. These compounds are usually only found in the plant’s stems and foliage, but under certain stressful conditions, they can find their way into the fruits or parts of them, making them taste bitter.

Cucumber plant stress and the subsequent bitter tasting fruits can be caused by a variety of factors, including poor watering, temperature fluctuations, a lack or imbalance of soil nutrients and even pests and disease.

Another issue that can cause cucumbers to taste bitter is cross-pollination. Indoor cucumber varieties intended for greenhouse cultivation are often bred to only produce the fruiting female flowers that do not need pollinating, known as parthenocarpe varieties. As a result, it is generally recommended with these cultivars to remove any male flowers that appear during the growing season, as pollination can cause the fruits to become bitter tasting.

Are bitter cucumbers safe to eat?

Unfortunately, the only way to tell if a cucumber is bitter is to try it. When a cucumber fruit becomes bitter due to the cucurbitacin, the bitterness is usually only in the skin and top of the cucumber, so peeling and eating the central parts may taste better.

Is it safe to eat a bitter cucumber or is it poisonous? It is widely agreed that a small quantity, as long as it looks healthy, is not toxic and will not affect adults. However, larger portions can be. Do not let children eat bitter cucumbers.

In some parts of the world, bitter cucumbers are even thought to have some health benefits. The Asian bitter cucumber (Momordica charantia), sometimes known as balsam pear, is different to our typically homegrown cucumber, but it is also a member of the cucurbit family. Its fruits, like cucumbers, are long and pale green, but they have a warty skin that makes them easy to identify. The fruit has a distinctly bitter taste and is widely grown in Asia and the Caribbean for its health benefits, which include lowering blood sugar and cholesterol levels.

How to make cucumbers less bitter

Choosing the correct cucumber variety is the first step in avoiding bitterness. Older varieties, especially heirloom cucumbers, tend to be more susceptible to stress and also often produce both male and female flowers, which following pollination can cause the fruits to be bitter. If you want to grow these varieties, make sure to look for and remove any male flowers are soon as they appear.

If you are not sure how to tell the difference between male and female cucumber flowers, or if you would rather not have to remove them, a simpler solution is to only grow a female only variety. This will prevent any pollination. Another option is to choose bitter-free cultivars.

Caring for your cucumber plants correctly helps to minimise any stress and also helps prevent your cucumbers from tasting bitter. One of the most common causes of cucumber stress is over or under watering as cucumber plants require their soil to be kept moist to grow well. However, they will struggle if their root systems become waterlogged or dry out completely. Water temperature also plays a role, as overly cold water can severely stress the plants, causing growth irregularities and bitter cucumbers.

Unsurprisingly, pest and disease damage can also cause cucumber plants to struggle, leading to stress and bitter tasting cucumbers. Cucumber plants can succumb to a number of different diseases and pests, which are far better prevented where possible because treatment options are limited. See our specialist article for help with identifying and treating cucumber diseases.

Cucumbers prefer a steady temperature and high levels of humidity when grown in a greenhouse or polytunnel. Extreme temperature fluctuations can cause stress, so aim for a consistent temperature by increasing airflow and dampening down during the day and closing any doors or windows at night when temperatures drop. Lightly mist the cucumber plants or dampen the ground during the day to increase humidity, but be careful not to soak the foliage, which can lead to mildew.

Providing enough nutrients is also a key part of growing healthy cucumber plants and helping them remain stress free. Planting cucumbers in a good quality compost will provide enough essential nutrients to get them off to a good start, but it is best to fertilise them with a nitrogen and potassium rich liquid or granular food. Our slow-release Plantura Tomato Food is ideal for feeding cucumbers and could not be easier to use as it only needs to be applied twice during the growing season. Read our other article for more advice on how and when to feed your cucumber plants.

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If you find that your cucumbers do not taste as expected, do not be too disheartened; usually not all of the fruit is bitter and parts can still be salvaged and relished.

Cucumbers can benefit from companion planting, as companion plants can naturally repel pests, attract pollinators, and even give them the nutrients they require to develop.

Find out more about companion planting with cucumbers, including what to grow with cucumbers and what not to grow.