Cucumber plants thrive when planted in rich soil that provides plenty of water and nutrients. Inconsistent or overwatering causes soil to become water-logged, which deprives roots of oxygen and can lead to root rot disease or other problems that inhibit a plant’s growth or cause yellow leaves. Watering too little can also result in the same problem. In both cases, the cucumber plant loses its ability to photosynthesise, which causes it to wilt and yellow. This is called chlorosis and it is a clear indication that the plant is starving for food.

If the leaves are cucumber plant yellow leaves to curl, it may be a sign of potassium deficiency. To correct this, apply a fertiliser containing potassium regularly to the garden. You can use a commercial formula that lists the ingredients as nitrogen, phosphorous and potassium or make your own organic fertilizer with compost or coffee grounds.

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Another cause of yellow leaves is low light exposure. If the plants are indoors, move them to a sunnier location or invest in supplemental lighting. Outdoors, try to give them 6 – 8 hours of sunlight each day.

Pests and diseases are also known to cause discolouration in cucumber plants, particularly downy mildew. This fungal disease causes a powdery coating on the underside of cucumber leaves, which can turn yellow or brown in spots. It’s important to choose resistant varieties like ‘Marketmore 76,’ ‘DMR 401,’ or ‘NY 264’ when planting and avoid humid, warm environments where the disease thrives. You can also try to increase air circulation around your cucumber plants and spray them with a fungicide.