Cucumber Leaves Turning Yellow – Causes Of Yellowing Leaves?

You’ve cultivated your dream garden – tomatoes, squash, and cucumbers galore. But what’s that? A yellowing cucumber leaf. Then two, three, and four leaving you wondering why.

Yellow spots and yellowing cucumber leaves can be stressful, especially after months of planting, watering, and pruning.

leaves on cucumber turning yellowPin

There are many potential culprits of the yellowing cucumber leaf. That’s why we’re on the case to help you diagnose why your cucumber leaf has lost its green sheen.

What Is Leaf Yellowing?

The yellowing of cucumber leaves is due to a deficiency called chlorosis. This is a condition in which the leaves lack chlorophyll, the green pigment found in plants.

Chlorophyll is an essential tool for plants during photosynthesis. Without it, plants are unable to absorb energy from light sources efficiently.

Many factors can cause chlorosis – the presence of pests or diseased plants or nutritional, light, or water disruptions.

What Damage Does Yellowing Leaves Mean?

So let’s dig in. What hints is your yellowing cucumber plant giving you?


If your cucumber plant leaves are yellow, you may have a  whitefly infestation. Whiteflies, small and triangular pests, devour the underside of leaves. They tend to gravitate toward indoor or greenhouse plants.

Another possible pest is the southern corn rootworm. These are the larvae of the cucumber beetle. They feed on the root of the cucumber, obstructing the plant’s proper use of water and causing yellowing.

Spider mites also infect plants by sucking on the leaves. These mites are identifiable by the thin and transparent webbing they leave behind.

Beetles may also attack – like the Striped Cucumber beetle.


Cucumber plants are also prone to downy mildews, which is a pathogen related to algae.

Water-soaked yellow lesions on the leaf’s underside is a sign of a downy mildew infection. The lesions are angular and confined within the veins of the leaf.

At times, the lesions can turn to brown spots. Other times, the lesions can appear grayish or fuzzy-looking.

There are also bacterial wilt, fusarium wilt, and verticillium wilt.

Nutrient Deficiency

Yellowing cucumber plants may also be suffering from one of several nutritional deficiencies.

Potassium Deficiency

One of the most common defects is potassium deficiency. Cucumber plants need more potassium than nitrogen. The potassium acts as an enzyme-activator, water-regulator, and protein-synthesizer within cucumber plants.

When cucumbers are low in potassium, the leaves will crumple and freckle. The cucumbers may also have a sponge-like texture.

Iron Deficiency

A cucumber plant with yellow leaves and green veins indicates an iron deficiency. This deficiency affects nitrogen metabolism in both the plant roots and leaves.

Nitrogen is a major component of chlorophyll, proteins, and plant growth.  Lack of iron causes chlorosis.

Nitrogen Deficiency

Cucumber leaves turning yellow also signals the potential of a nitrogen deficiency.

A lack of nitrogen may stunt the plant’s growth and the oldest leaves will begin to yellow. In severe cases, the entire plant will turn white.

Zinc Deficiency

In the case of a zinc deficiency, the leaves will freckle with yellow hues. Additionally, leaf size will remain small.

Light and Water-Related Yellowing

If your cucumber plant does not receive enough sunlight, it may begin to yellow. A cucumber plant requires six hours of direct sunlight a day.

Overwatering your plant, or poor soil drainage may also deprive its roots of oxygen. Cucumber plants only need one to two inches of water a week to grow well.

How to Control and Prevent Yellowing Leaves

Yellow cucumber leaves are always an indicator of a larger problem. But, there are a few simple tricks that can help improve your plant’s health.

Remove pests using various natural remedies, which include applying to leaves:

Or, bury a clove of garlic in the soil to mitigate the migration of pesky pests.

If your plant suffers from a potassium deficiency, treat it to a base fertilizer with high potassium levels. It may also be helpful to treat the soil for acidity or alkalinity.

Adding a nitrogen-rich fertilizer or ammonium nitrate may also help plants that are nitrogen deficient. Apply a tablespoon of ammonium nitrate once the flowers begin to bloom. Then apply again three weeks later.

Iron deficient? Add granular chelated iron to the soil around the roots, or spray liquid iron onto the plant.

Additionally, if you see any hint of decay or disease, it’s essential to remove the affected leaves before the lesions spread to the rest of the plant.

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