Why are Cucumbers Bitter?

 Usually, the bitterness is caused by some climate or soil condition that could be easily solved. That's why it is so important to take preemptive steps to keep them from becoming bitter in the first place.

Cultivated cucumbers all contain cucurbitacin B and cucurbitacin C, compounds that are supposed to make their leaves bitter and less tasty to munching animals. These compounds are usually confined to the leaves and stems of the plants, parts of the plant humans don't eat, so we are not aware they are there. It is only when they move into the fruits that we start detecting a bitter taste. Usually, it is not the whole fruit that turns bitter. More commonly, the bitterness will be concentrated at the stem end and the area right under the skin.

There is still some disagreement about what causes the bitterness to spread into the fruits, but it seems to point to types of stress while the cucumbers are growing. So although we cannot correct the problem after the fact, we can try and avoid the following 3 growing conditions that are potential culprits of bitter cucumbers.

Dry Conditions: Long periods of hot, dry weather can contribute to bitter cucumbers. 

Lean Soil: Another factor in bitter cucumbers is lean soil and a general lack of nutrients.

Lack of Sun: Overcast areas, like the Pacific Northwest, have reported bitter cucumbers due to lack of sun. 

Finally, look for varieties that are well-suited to your area and that are labeled "non-bitter". Some reliable varieties are 'Marketmore 97', 'Diva', 'Eversweet' (any variety with "sweet" in the name), 'Long Green Improved', and the heirloom 'Lemon'.