Why Are My Cucumber Leaves Turning Yellow?

Last Updated 7/2/2022

I remember the first time I saw yellow foliage ​on my cucumber ​plants. The cucumbers ​were freely climbing, clinging, flowering and giving a bounty of ​fruit on ​trellis I built.

​​It baffled me and caused me to ask Why are my cucumber leaves turning yellow?

​You will ​learn some of the common causes of cucumber leaves turning yellow and some solutions that ​I rapidly employ to fix things.

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What is The Cause For Leaves Turni​ng Yellow

The most common reason why cucumber plants ​turn yellow, is because moisture stress has set in or a nitrogen deficiency

Surprisingly, ​cucumber leaves turning yellow can be caused by over watering or not watering your plants with enough water. The very first thing you should check is the container or pot you planted your cucumber plants in.

​Simply add more water to your cucumber plants if turning yellow.

​The problem is that your cucumber plants ​are not getting the right amount of water.

Make sure you water the cucumber plants ​​at regular intervals.

​Don’t forget though that too much water or over watering can also cause the yellowing of the ​plants.

If over watering of your cucumber plants is your problem then you just have to reduce the amount of water you put in the pot or the soil. You can add the right amount of water or water you plants less often.

Your nitrogen deficiency can usually be cured with some addition of nitrogen to the soil for your plants.

Plant Diseases

In many cases, diseases of the plants are often the cause for ​cucumber’s leaves turning yellow. You should make sure your cucumber plants are not infested with these diseases:

Cucumber Mosaic Virus

Cucumber’s leaves ​are wrinkled and curving downwards with yellow spots dotting the leaf surface.  The plants could also have evolved to have brown spots as it progresses. 

The cucumber mosaic virus may have arrived on your plants.

The virus is ​​not treatable and the only option is to remove the infected plants from the garden. If you leave the plants in the garden the virus will most likely spread by aphids and leaf hoppers.

You should be aware that the virus is able to live in the soil and infect new plants the year after.

Fusarium Wilt

This next virus is similar to the above and usually develops on the older leaves & plants. If ​your cucumbers are all turning yellow beginning from the edges towards the center of the leaf, your plant is infected with the Fusarium.

The only way to deal with this problem is also to get rid of the infected plants like the Mosaic wilt and there are options of how to go about it.

The verticillium wilt is another similar fungus that favors areas once used for growing vegetables such as potatoes, peppers, tomatoes, eggplants & a few other plants.

Downy Mildew

The presence of ​the downy mildew virus on your plants is betrayed by leaves turning yellow with spots. ​

The spots are usually present on the upper surface of leaves ​and later turns brown.

The leaf veins bind these yellow spots at an angle giving the impression of a patchwork.

downy powderey mildew

It shows itself well during high humidity appearing on the underside of the leaves of your cucumbers & plants.

Treatment of Plant Diseases:

  • Planting varieties of cucumbers plants that have strong disease resistance levels
  • Air circulation around cucumber plants improved and leaves kept dry with wide row spacing and use of drip irrigation.
  • Immediate removal of the infected plants that turn yellow to prevent spreading of the disease & promote further growth.
  • Early application of systemic and contact fungicides. Soil health is essential to prevent disease & promote growth for your ​cucumbers & plants.

Pest Issues

In addition to over watering and under watering causing the leaves of your cucumber yellow, pests are a potential issue.

The pests can ​have a disastrous effect on your cucumbers & plants.

They can also turn the leaves yellow in the following ways:

Microscopic Spider Mites

The​ spider mites literally suck the sap from the leaves of your cucumber plant.

You will know that these are responsible for attacking the leaves of your cucumbers when your cucumber leaves are populated with fine silvery webbing that is draped on the underside of your leaves.


These are also good at sucking the life out of the leaves of your ​cucumber plants. 

When you see your cucumber leaves develop a malformed curled downwards at the edges, you are being attacked by aphids. 

The stems and leaf backs are their favorite haunts and they mass in scores partaking in their favorite meal of sprouting new growth. As the feed, they excrete a cover of clear, mushy honeydew.


The most common evidence that tells you whiteflies have invaded your cucumber plant is the tiny white bodies.

You can dislodge them from their roost if you gently shake your cucumber plant.

You will immediately notice a cloud of very small whiteflies lift themselves aloft with their white wings into the air.

white flies

Like the aphids, they also love to leave honeydew behind. They also can lay eggs on the underside of the leaves.

Potato Leafhopper

The potato leafhoppers travel on the leaves of ​cucumbers & plants no matter which species and settles for a meal sucking the sap out of the leaves. 

They are much larger than the bugs already mentioned but they are happy munching away at the leaves of your plants. 

As they feed, they inject a yellowing toxin and with additional injections the leaves start to weaken and fall from your plant.  It will stunt the growth of your cucumbers.

Treatment of Pest Issues

  • Use insecticidal soap on the leaves of your cucumbers.
  • Spray your plants with a suitable solution until it  is dripping from the leaves and reapply the treatment again in line with the recommended frequency of spraying your plant shown on the packet label.
  • Row Covers are an all around solution for many pests especially at the beginning of the season.

​Insecticidal soap ​is not recommended for getting rid of the potato leafhoppers as you will eat the fruit sooner or later.  

However, you can get rid of all the weeds all around and use row covers as a way to keep the leafhoppers & other pests at bay.

Soil Nutrition Deficiency

Like all other plants, your cucumber plant needs different nutritional food & fertilizer to grow well. 

Cucumber leaves turning yellow is ​caused when the deficiency is ​high.

However, if the proper soil nutrition & fertilizer is not available, a disease called chlorosis will take place. In order for you to know the kind of nutrients that are present or absent in your vegetable garden plants, you must test your garden soil.

These are the most common deficiencies of soil nutrients that can turn cucumber leaves yellow:

Nitrogen Deficiency

Among other nutrients, the absence of nitrogen in the soil ​is responsible for cu​cumber leaves turning yellow.  ​A lack of nitrogen will also stunt the growth of your cucumber plant.

If you allow the condition to get really severe your plant will eventually succumb to its lack of nitrogen and die.

You should keep watch on the older leaves that turn yellow along the central veins and the tips of the ​cucumbers & plants. Newer leaves should continue to look green until they reach maturity. This sia sign of enough nitrogen for your plants.

Nitrogen deficiency can easily be resolved with the addition of extra nitrogen content into the soil.

All you have to do is add a 2 inch layer of compost high in nitrogen or simply add 1-2 tablespoons of 6-10-10 fertilizer the moment you notice the problem starting.


  • Add a tablespoon of ammonium nitrate once the flowers of your plant bloom.
  • Add another tablespoon of ammonium nitrate ​three weeks after the first lot.

Don’t put too much fertilizer in the soil because your plant may not produce its bounty of cucumbers if too much fertilizer is added. Keep to three weeks in between feedings.  Doing these suggestions will prevent cu​cumber leaves turning yellow & your cucumbers healthy.

Iron Deficiency

You will find evidence of iron deficiency if new leaves turn yellow but have green veins while older leaves remain green. 


  • Add granular or powdered chelated iron to the soil about the root area.
  • Alternatively, spray liquid iron on the plant.

Potassium deficiency

Cucumber plants need high doses of potassium and are the type of crops which need more potassium than nitrogen.

Cucumber plants become deficient in potassium when leaves turn yellow along the edges and at the tips. Young leaves are small cupped or puckered. 

The cucumber is malformed narrowing at the towards the stem in a club-shaped form.


  • A balanced fertilizer will solve the problem
  • Treat the soil for acidity or alkalinity if you deem it necessary.

Zinc Deficiency

You will know that your plants are suffering from zinc deficiency if the older leaves are turning yellow between the vein, the size of the leaves is small and plant growth restricted.


  • Spray with a solution of zinc sulfate will correct the problem or organic kelp.

Other Possible Causes

Water Related Yellowing

Over-watering your cu​cumbers will result in the depletion of oxygen around the root zone with the typical sign of leaf yellowing and wilting. 

With rainfall cucumber plants need only about 1-2 inches of water per week.


  • If drainage is the problem, mix sand with the soil to loosen it up. 
  • Alternatively you can plant your cucumber plants in raised beds.

Lack of Sunlight

Another cause for droopy yellow leaves on your cucumber plants could be the lack of enough sunlight.  Cucumbers need a good dose of sunlight each day.


  • Move your plants to a site to get a minimum of 6 hours sunlight every day.
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Final Thoughts

​Taking proper care of your cucumber plants is a must if you wish to have a bounty of cucumbers come harvest time for yourself and family.

There may be many obstacles that confront you from doing this but there are also solutions that you can use to achieve your goals that’ll help you never to shout and ask: Why are my cucumber leaves turning Yellow.

Green Thumb Gardener
cucumber leaves yellow
Jeremy Starke

We at Green Thumb Gardener provide tips and guides for both for beginners and advanced gardeners out there. 

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