All cucumber plants contain a substance known as cucurbitacin, which tastes very bitter and is toxic when concentrated. Normally, cucurbitacin is found in the roots, stems, and foliage of the plant, but in times of stress it may creep into the cucumber fruits, as well.
Usually the cucurbitacin content of a cucumber is so low that the chemical cannot be tasted and no side effects (upset stomach, burping, cramps, diarrhea) occur from eating it, but many gardeners have had the misfortune of picking cucumbers with a distinctly bitter flavor. What causes this?
Experts are not entirely in agreement on the cause of bitterness in cucumbers. It appears that flavor is produced by a complex interaction of circumstances.
Here are some of the factors which influence cucumber taste:
- Variety. Choose a cucumber variety that is low in cucurbitacins. Burpless cucumbers have less obtrusive levels of the offending chemical, while bitter-free cukes never have cucurbitacins in the fruit. Gardeners have consistently proven that variety is the most important factor affecting taste.
- Temperature. Excessive heat, unseasonably cool weather, and wild swings of temperature can all stress cucumbers, increasing cucurbitacin levels. If your summer highs are typically in the mid-90s or higher, provide some shade for your cucumbers. If cool weather is consistently a problem, choose a variety that doesn’t mind lower temperatures. Unfortunately, there is little that a gardener can do about variable weather, except choose a more forgiving variety.
- Water. Either drought or irregular periods of wet and dry weather can increase cucurbitacin levels in the cucumbers. Don’t let your plants go too long without water. Keeping the soil slightly moist (but not soggy) at all times is recommended. Mulch helps to even things out.
- Soil health. Healthy soil produces tasty cucumbers. Check your soil fertility and pH to see if this could be the source of the problem.
- Competition. Weeds are stressful to cucumbers. They compete for valuable water and nutrient resources, and they harbor insect pests. Keep the weeds in check. For the same reason, make sure you space your cucumbers according to the directions on the seed packet.
- Ripeness. As cucumbers mature, cucurbitacin levels rise. Don’t let your cucumbers get too big. Most slicing varieties should be picked when they are between six and eight inches long.
- Storage. The longer a cucumber sits in the refrigerator, the more its cucurbitacins will concentrate. Try to eat your cukes while they are still fresh.
If you experience weather conditions that are likely to stress your cucumbers, take a few steps to reduce the quantity of cucurbitacins that you are going to eat. Most of the chemicals are concentrated at the ends (particularly the stem end) and directly under the skin of the cucumber. Peel the cuke well, chop an inch off the stem end, and slice the other end off, too. If it still tastes very bitter throughout, the plant is either in bad health or genetically predisposed to bitterness. You might want to pull it up and try again next year, preferably with a different variety.
Keep in mind that, while many factors affect cucumber flavor, cucumbers will not become extremely bitter unless they are genetically predisposed to do so. Some varieties never develop a bitter taste even under adverse conditions. Therefore, while you should be careful to keep your plants healthy through proper watering and soil building, choosing a variety better suited to your taste buds and climate is the only reliable solution.