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Causes & Prevention of Bitter Tasting Cucumbers

Bitter CucumbersGrowing your own cucumbers usually produces lovely fresh fruits but sometimes you’re shocked by an awful bitter taste. This article explains the causes of bitterness in cucumbers and how to prevent bitter cucumber.

What Makes a Cucumber Taste Bitter

Cucumbers are members of the cucurbit (Cucurbitaceae) along with marrows, courgettes squash and pumpkins. To protect the plant from being eaten this family produce a very bitter tasting chemical called cucurbitacin which is usually limited to stems and leaves. Oddly and unusually, I have a cat that loves the taste of cucurbitacin and eats the leaves given a chance.

Sometimes the cucurbitacin gets into the fruit making the cucumber inedible. It can be limited to the ends or one end of the cucumber or the whole of the fruit may be affected.

Causes of Bitter Cucumber

Older greenhouse cucumbers often produced bitter cucumbers because the plants had both male and female flowers. Pollinated female flowers produced the bitter cucumber fruits so with those old varieties the male flowers had to be removed. Just missing one or two male flowers could be enough to spoil a flush of fruit.

To identify which sex the flowers are look for a tiny fruit behind the flower. This shows the flower is female as the males lack this immature cucumber. The male flowers just have a stalk connecting them to the plant, often thinner than the female. The males sometimes grow in a group but females are always on their own.

Modern all-female varieties do not have this problem but they can still produce bitter cucumbers or partly bitter cucumbers if the plant is stressed. Stress can be caused by a number of factors:

  • Conditions too cold
  • Conditions too hot
  • Conditions varying between very hot and cold (early season sunny days with cold nights)
  • Physical damage to the plant (such as a crazy cat eating the leaves!)
  • Drying out or drying and flooding the plant
  • Lack of nutrients, especially nitrogen
  • Bad cases of powdery mildew reducing effective leaf area late season
  • Bad red spider mite infestation

Prevention of Bitter Cucumber

By following the items below you can prevent bitter tasting cucumbers.

If growing an old heritage variety of cucumber, ensure you get all the male flowers as soon as they appear.

Pay attention to the temperature, using the vents on your greenhouse to keep them from overheating in the day and closing them on cool nights

Water regularly, preferably little and often or twice a day rather than a good soaking every couple of days and letting the plant dry out in the meantime.

Cucumbers love a humid atmosphere and react well to misting which will have a side benefit of deterring red spider mite.

If your plants start with powdery mildew, spray with a solution of skimmed milk diluted 1:5 in water or chemical fungicidal control of your choice. Do not overcrowd plants as limited airflow encourages spread of mildew.

Feeding is important to producing healthy, bitter-free cucumbers. Usually gardeners just feed with tomato feed and most often get decent results but ideally you should use a feed higher in nitrogen like nettle tea, Miracle Gro or Chempack No. 2 (High Nitrogen) as part of your feeding regime. This will prevent nutrient stress and thereby prevent bitterness in cucumbers.

Finally About Bitter Cucumbers

After reading this you may think cucumber growing is really difficult and you’re going to have bitter cucumbers at best. Don’t worry, bitter cucumbers are actually not common at all.

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