The Ultimate Guide On Why Your Cucumber Leaves Are Turning Yellow

The Ultimate Guide On Why Your Cucumber Leaves Are Turning Yellow (1)

It’s the middle of spring, and your cucumbers have begun to grow either outdoors or in your greenhouse. They’d look almost perfect if it weren’t for the leaves, which are starting to turn yellow.

Does this mean your cucumber is turning rotten, or that it won’t be edible by the time it’s ready to be harvested?

Cucumber plants, as with most plants, use their leaves as a form of communication. You often won’t know what’s wrong with a plant until you look at the leaves, which will change in color, shape, and texture if there is something wrong with the plant.

Knowing how to read these signs will help you nurse the plant back to health. 

So, if you’re concerned with the yellowing leaves of your cucumber plant, you’ve come to the right place. Here is the ultimate guide on why your cucumber leaves are turning yellow!

Why Are My Cucumber Leaves Turning Yellow?

Inconsistent Watering

One of the main causes of yellow leaves on a cucumber plant is that you’re not committing to a good watering routine.

Leaves will turn yellow if the plant is dehydrated, so if you spot yellowing patches on your cucumber leaves, it’s time to give the plant some water. 

Cucumbers require about 1 to 2 inches of water a week to grow healthily. Commit to a regular watering schedule, and make sure that the cucumber is growing in well-draining soil to prevent water logging.

Because cucumbers love water, it might be worth investing in a drip irrigation system – especially if you have to water lots of plants at a time. 

However, yellowing leaves can also be a sign of overwatering, so make sure to only water the cucumber once a week. 

Plant Diseases

Unfortunately, cucumbers are prone to developing plant diseases, most notably cucumber mosaic virus. They can also be infected by mildew and wilt. 

Cucumber Mosaic Virus

A clear sign of cucumber mosaic virus is when the leaves exhibit yellow dots, mottling, distortion, flecking, and strange mosaic patterns in various colors.

This virus is spread by aphids, and spreads like wildfire amongst cucumbers and other plants. 

Unfortunately, there’s not much you can do about cucumber mosaic virus other than to remove the entire cucumber plant and other plants that have been infected.

You will also have to re-soil the area, as the virus will live in the soil and can infect new plants that you plant there. 

Sadly, there is no cure for cucumber mosaic virus, so you will have to say goodbye to your plant if it becomes infected. 

Downy Mildew

Downy mildew occurs in humid or excessively wet conditions. It appears on cucumber leaves in the form of yellow spots. Without treatment, or in extreme cases, the leaves will turn completely brown. 

So, the best way to prevent downy mildew is to plant mildew-resistant cucumber varieties.

If you plant more than one cucumber, space them out so there is enough room for each plant to breathe and dry out after a watering session. 

The key is to keep an eye on your cucumber plants to spot the signs of mildew. In the early stages, you can catch the mildew with fungicides.

If the plant has been completely infected, however, you will need to remove it from the area. 

Fusarium Wilt 

Caused by a type of fungus, fusarium wilt affects the vascular system of a plant. Mature cucumber plants that are infected with this wilt will possess yellowing, wilting leaves.

Unfortunately, there’s nothing you can do to save a cucumber plant infected with fusarium wilt. 

Once infected, the plant will die within 3–5 days, and will need to be removed. 

Nutritional Deficiencies

One of the most important parts of gardening fruits and vegetables is ensuring that the soil is suitable for the plant species, well-draining, and filled with nutrients.

Without these nutrients, the plants cannot grow to their full potential. 

Here are some of the most common deficiencies in cucumbers. It is worth completing a soil test to see exactly what the plant is deficient in, so that you can make the necessary steps moving forward. 

Potassium Deficiency

When cucumbers begin to flower, they need higher amounts of potassium. If you provide your cucumber plant with lots of potassium, it will result in high yields. 

Without a sufficient amount of potassium, the leaves of a cucumber will turn yellow at the tips and edges. To combat this, use a fertilizer that is well-balanced in nutrients, and rich in potassium. 

Nitrogen Deficiency 

Nitrogen deficiency in cucumber often presents itself in the form of yellowing leaves. This is because nitrogen is responsible for the foliage and overall plant growth.

So, with a lack of nitrogen comes unhealthy leaves, and the eventual death of the plant. 

To combat this, add nitrogen to the soil with two tablespoons of fertilizer.

This fertilizer needs to have a ratio of 5-10-10, and you have to follow the instructions on the fertilizer package to prevent causing further harm to the plant. 

You’ll know that the cucumber is receiving the nitrogen when it begins to flower. Then, add a tablespoon of ammonium nitrate to the soil, and repeat after 3 weeks.

If you want a non-chemical solution, you can add a thin layer of compost to the soil around the cucumber. 

Iron Deficiency

Just like with humans, cucumbers can also be deficient in iron. This deficiency appears in the form of new leaves that are yellow with green veins.

The best way to combat an iron deficient cucumber is to spray the leaves with liquid iron, or sprinkle granular iron around the roots. 

The Ultimate Guide On Why Your Cucumber Leaves Are Turning Yellow


Just like any other plant, cucumbers are prone to attracting several pests. Fortunately, most of these pests are easy to deal with. 

Spider Mites, Aphids, And Whiteflies 

Spider mites, aphids, and whiteflies are among the most common pests found on most plants, fruits, and vegetables.

These pests like to feed on the sap on cucumber leaves, which can cause the affected areas to turn yellow. 

While they might seem harmless and easy to get rid of, you need to act fast with these pests, because they can eventually kill the cucumber plant. 

The best way to get rid of spider mites, aphids, and whiteflies is to spray an insecticide soap onto the leaves.

Make sure to follow the directions on the product’s packaging, because you might need to dilute the soap to prevent bleaching the leaves with harsh chemicals. 

Potato Leafhoppers 

Just like spider mites, aphids, and whiteflies, potato leafhoppers are attracted to the sap on cucumber leaves. However, these pests are more damaging to the plant than other pests. 

When they eat the sap, they inject a type of watery saliva into the leaf. This is what causes them to turn yellow, and will eventually lead to the leaves falling.

If you catch the early signs of this, you can try to treat the infected areas with insecticidal soap, but you might be too late. 

As a preventative measure, you should use row covers to protect your cucumber plants from potato leafhoppers.

You should also encourage insects that eat these pests into your garden or greenhouse, such as ladybugs and lacewings. 

Limited Access To Sunlight

Cucumbers are known for loving sunlight, so if you have planted them in a shaded part of the garden or greenhouse, they won’t be happy.

Cucumbers that don’t receive enough sunlight will start to develop yellowing leaves, and might have issues with draining the water in the soil. 

Ideally, plant the cucumbers in a position that receives at least 6 hours of sunlight a day. The best cucumbers will grow in 8 hours of sunlight a day. 


So, there you have it! Cucumbers aren’t the most difficult vegetables to grow, but it’s really important to check up on the quality of the leaves regularly. These plants use their leaves as a form of communication to tell you when something is wrong. 

Whether it’s a matter of under-watering or the plant has developed a disease, hopefully this guide has helped you find the right cure for your cucumber plant. 

Frequently Asked Questions

What Do Overwatered Cucumber Leaves Look Like?

Cucumbers love water, but they shouldn’t receive more than 1–2 inches of water a week.

If you overwater your cucumber, the leaves will start to turn yellow and wilted, and will eventually turn brown. The same happens when you underwater these vegetables. 

If you spot the early warning signs of yellowing leaves, cut back on watering for a while. You’ll need to remove any dead leaves to encourage new growth, because they will be wasting the energy of the plant. 

Should I Cut Off Yellow Cucumber Leaves?

If your cucumber leaves are completely yellow and wilted, you should cut them away from the plant.

This is to help encourage new growth, because the plant will no longer be using all the nutrients to try and heal itself. You have to be cruel to be kind in the plant world!

When cutting off yellow cucumber leaves, use a disinfected sharp knife or scissors and cut the leaf at the root. This will also help the air circulation of the cucumber plant, which should encourage a higher yield of cucumbers. 

How Often Should You Water Cucumbers?

You should water cucumbers once a week. These vegetables love water, and require deep watering at a consistent rate.

During summer or a hot spell, the frequency of watering will need to be increased.

If the cucumbers don’t receive enough water, or if the watering is too inconsistent, the leaves will turn yellow and the quality of the vegetables won’t be high.

About The Author

Gina Harper grew up dreaming about farms and growing her own food. She began an urban garden to feed herself and turned it into an incredible hobby. Gina is here to teach you everything from raised beds to container gardening, how to keep plants alive and well in a smoggy city, and the works. It’s time that we carve our own piece of green earth and reap what we sow—she’s here to help you with that.