Are Your Cucumber Leaves Turning Yellow? 6 Reasons Why

Did you discover your cucumber leaves are turning yellow? Don’t panic; here are some common reasons this happens in your garden.

Homegrown cucumbers taste better than any cucumber you’ll find at the store, but when you find your cucumber leaves turning yellow, you worry about the future of your plants.

Growing cucumbers is a struggle for many gardeners. Not only are these plants heavy feeders, but they also need plenty of moisture. In many cases, a lack of nutrients or moisture could cause the cucumber plant leaves to turn yellow.

Of course, there are other reasons as well for cucumber leaves turning yellow like pest infestations or diseases.

If you notice the leaves changing to yellow, here are some causes and how to fix the leaves, and hopefully, save your harvest.

Related: Did You Find Tomato Leaves Turning Yellow? Here are 10 Reasons!

6 Reasons for Cucumber Leaves Turning Yellow

1. Not Enough Sunlight

The first thing you should do if you notice cucumber leaves turning yellow is to make sure the plants receive the right amount of sunlight.

Cucumber plants are sun-loving, and they need to be planted in an area that receives a minimum of six hours per day of sunlight. The plants often grow better if they receive eight hours or more of sunlight.

However, if your plants are in the ground, you may not be able to move them. Consider removing plants nearby that might block or decrease the sunlight your cucumber plants need.

2. Watering Problems – Too Much or Not Enough

The curl + the yellowing indicates that I may not be watering these plants enough!

We all know that cucumber plants need water, but sometimes, too much or not enough of a good thing is a problem. That’s why it’s a common source of cucumber leaves turning yellow.

Inconsistent watering will lead to problems; cucumber plants require a minimum of one to two inches of water each week to grow to optimal conditions. So, if you aren’t watering as much or receiving less rain than before, you might need to water more often.

On the other hand, too much water is just as bad. Cucumber plants dislike waterlogged, soggy feet. If your plants receive too much water – either from you or rain water – it causes the roots to become oxygen deprived. This causes leaves to turn yellow or wilt.

Make sure the soil is draining. If it’s not, then you can try to loosen the soil with sand and add compost to your garden soil. Doing this helps with soil drainage.

Here are some other suggestions!

  • Water on a regular schedule, taking into account rain you receive. Use a rain gauge to keep track of how much rain your property receives.
  • If you have trouble with soil drainage, consider growing cucumbers in following years in raised beds.
  • Use a soil moisture meter to keep track of the moisture in your garden beds. This prevents over and under watering.

3. Nutritional Deficiencies

Nutrients are an essential part of the soil that makes your plants grow and thrive. Without proper nutrients, plants struggle to reach their peak. This is why it’s essential to conduct a soil test before planting to determine what nutrients your plants need; a soil meter is great for this!

Testing your soil lets you know if you need to add more nutrients to your soil before planting. If you didn’t do so, it’s possible your cucumber plants are suffering from a nutritional deficiency, and that may cause cucumber leaves turning yellow.

Related: 10 Best Fertilizer for Cucumbers for Bigger Yields & Better Growth

Nitrogen Deficiency

Nitrogen is one of the big players in soil, and if any plants suffer from a nitrogen deficiency, leaves may turn yellow. It is essential for you to correct this problem because plants die from a lack of nitrogen.

Nitrogen is responsible for the growth of your plant and the foliage; cucumber plants need nitrogen for the vines to grow and crawl up the support system.

The easiest way to remedy this problem is to add nitrogen to your soil around your cucumber plants. Most cucumber fertilizers have nitrogen added into the composition, or you can grab a 5-10-10 fertilizer. A liquid fertilizer will have the fastest affect on your plants, and consider adding a side dressing of compost around your plants.

If you notice that the yellowing stops after application, continue to reapply fertilizer every two to three weeks to ensure the soil has enough nitrogen.

Related: 11 Natural Nitrogen Sources All Gardeners Need to Know

Potassium Deficiency

Once your cucumber plants start to flower, they require higher amounts of potassium. So, if your cucumber leaves turn yellow after flowers appear, your plants may be struggling with this deficiency.

Another sign of a potassium deficiency is that the leaves turn yellow at the edges and tips.

Luckily, fixing this problem is easy; all you have to do is use a fertilizer with plenty of potassium, and I suggest using a water-soluble fertilizer that absorbs fast into the soil.

Other Nutritional Deficiencies That Cause Cucumber Leaves Turning Yellow

Plants need more than NPK, and some other deficiencies cause issues and may lead to cucumber leaves turning yellow. Here are others to consider.

🌱 Iron Deficiencies: if your plant has an iron deficiency, you’ll notice that the new leaves are yellow but have green veins still. It’s possible to remedy this by spraying the foliage with liquid iron or sprinkling granular iron around the roots of your cucumber plants.

🌱 Zinc Deficiencies: If your plants suffer from a zinc deficiency, the older leaves turn yellow between the veins. You may also notice the size of the leaves are smaller than they should be, and the overall growth of the plant is restricted. Try treating the plant with a solution of zinc sulfate or organic kelp.

4. Chlorosis

Chlorosis is a plant condition that causes the leaves of a plant to produce insufficient levels of chlorophyll. I bet you heard of chlorophyll in your middle school science classes; it’s the green leaf pigment that grabs sunlight to create food for the plant.

If a plant has insufficient chlorophyll, cucumber leaves start turning yellow, indicating that they are starving without food.

You have to figure out what is causing the chlorosis; study the plants for other signs. Many plants with this condition suffer from iron deficiency, which is treatable with sprays.

5. Cucumber Plant Diseases

Cucumber mosaic virus took over this area in my garden last year.

All plants are susceptible to plant diseases, and cucumber plants have a few common diseases that like to strike that may cause yellowing leaves.

Cucumber Mosaic Virus

  • Symptoms: Wrinkled leaves curved downwards, brittle, yellow spots

If you notice your cucumber leaves have a mild mosaic pattern, mottling, or flecking, it’s an indicator of cucumber mosaic virus.

Aphids spread this virus around, and it’s possible for all of your plants to be infected within a few hours. It’s bad news for your garden, and the worse news is that the only thing you can do, since this is a virus, is remove all of the plants and weeds in that area.

Cucumber mosaic virus lives in the soil for at least a year, and if you put cucumbers back in the same place, it may infect your plants the following year. This is why crop rotation is essential!

Solution: Pull all the affected plants. Since no chemical treatments work for, you don’t want to leave any infected plants in your garden.

Downy Mildew

  • Symptoms: Yellow spots on the leaves that turn brown. Gray fuzz on the underside of the leaves.

Another troublesome cucumber disease is downy mildew, a pathogen that thrives in wet, humid conditions. You always want to make sure your plants have air circulation to avoid this troublesome disease.

You might notice yellow sports forming on the surface of the cucumber laves, and over time, the leaves will turn brown. The leaf spots are angular, bounded by leaf veins.

Thankfully, you can try tackling this problem, and downy mildew rarely survives on plant debris. So, chances of it living in your garden overwinter is slim.

If you find that your cucumber leaves turn yellow, grab a liquid fungicide and spray it on your plants. The sooner you catch this disease, the easier it is to treat.

Fusarium Wilt

  • Symptoms: Some yellowing leaves, some turning dull gray-green. Dark spots on the lower part of the stem.

Fusarium wilt is a fungal infection caused by the fungus Fusarium oxysproum. It’s possible for this fungus to live in the soil for long periods because the spores are durable, and they may live in plant debris.

This fungi affects the vascular system of the plant, and it’s a death sentence to your plants. Any infected plants have to be removed from your garden.

Fusarium wilt may cause damping off in young plants. Older plants may have yellowing leaves, stunted growth, and wilting. If the plants start to wilt, they will die within the week. It’s best to rip them out to prevent the spread of this fungus in your garden.

6. Pests Attacking Your Cucumber Plants

This is cucumber mosaic virus. I won’t be planting cucumbers in this area again for awhile.

Cucumber plants aren’t immune to pests, so if insects are eating your plants, it could cause cucumber leaves to turn yellow. This is particularly true for any insects that feed on the sap of leaves.

Spider Mites

Spider mites cause all sorts of problems for cucumber plants. They suck the sap out of the leaves, hanging on the underside of the leaves while leaving a silver web on the leaves.

Mites appear on plants between late June and August, and they tend to infect your plants in hot, dry weather. Adult spider mites are very tiny with varying colors from yellow to dark red.

Since spider mites feed on the leaves, causing the cucumber leaves to turn yellow. In bad infestations, the leaves may dry and fall off the plant.

Here are some things you can do to treat a spider mite infestation.

  • Spray the affected plants with neem oil, which is not a harmful product to your plants or you!
  • Try a spray designed for spider mites; this Bonide Mites X-Ready is a highly-rated choice.
  • Apply insecticidal soap to your plants, or try a DIY insecticidal soap.

No matter which of these products you try, make sure you apply to the top and bottom of the leaves. Heavy infestations may require several applications.


Many plants are prone to aphid infestations; cucumber plants are one of those. These hungry pests suck out your plants nutritional sap, leaving a residue of honeydew in their wake. Honeydew attracts ants and black sooty mold, two problems you really don’t want!

Related: Ants in the Garden: 11 Natural Methods to Try

Aphids are ridiculously tiny, oval-shaped insects that are often hard to spot because they are green in coloring. Sometimes, they might be black or red, but most tend to be green.

Aphids also typically live on the underside of leaves, making them to harder to spot as you inspect your plants.

Typically, an aphid infestation is only a concern if it grows into large numbers. At that time, I suggest using one of these products to get rid of these troublesome pests.


Whiteflies are another sap-sucking pest that will damage your plants if you get a large infestation on your plants. These pests have white bodies and wings.

Often times, when you shake your plant, these pests will come flying out, a sure sign that you have a whitefly infestation.

The above products all work for whiteflies as well, but if you have these pests in your garden, you have another option as well. Reflective mulches are a great way to combat whiteflies without needing spray your garden.

Cucumber Beetle

One pest you don’t want to see on your cucumber plants is the cucumber beetle. They will destroy your plants, including your squash plants, turning the leaves into a lacy, skeleton of holes.

Another problem with cucumber beetles is they often carry serious plant diseases. So, it’s in your best interest to take action as soon as you spot a single cucumber beetle. Take it off your plants and put the beetle into a cup of soapy water.

There are some other things you can try when you discover cucumber beetles in your garden.

  • Release beneficial insects into your garden. Braconid wasps love to feed on cucumber beetles.
  • Laying down a thick layer of straw as a mulch also helps prevent the beetles from moving to other plants.
  • Use floating row covers early in the season, after transplanting the seedlings into your garden, to prevent the young pests from landing on your cucumber plants. Just make sure to remove any floating row covers before the plants flower to allow for pollination.

Southern Corn Rootworm

Southern corn root worms are spotted cucumber beetles in the larva form that decided your garden soil is their home. These little pests will eat through the plant stem at ground level, slowing the overall growth of your plants.

Overtime, this infestation will turn the foliage yellow.

Unfortunately, the only thing you can do is remove the affected plants and turn the soil regularly to expose the larva to the sunlight. Typically, it’s recommended to deal with these pests by interrupting their life cycle.

Potato Leafhopper

Potato leafhoppers feed on the sap of the plants, but they also inject the leaves with a watery saliva that causes damage to the leaves. Over time, the leaves turn yellow and fall off the plant.

Typically, these pests attack potato plants, but if they find a cucumber plant, that’s good enough as well to them. The biggest problem with these pests is that they leave behind a toxic substance causing the leaves to yellow and drop off.

Spacing your plants well helps avoid these pests; they avoid areas with ample air circulation. Always remove weeds to keep these pests off your plants .

Typically, the best way to treat a potato leafhopper infestation is to use insecticides.

How to Determine Why Your Cucumber Leaves Are Turning Yellow

Now that you know all the causes, here are the steps to take to determine what is the cause of your plants’ problems.

1. Check for Pests

The first thing you should do when you find your cucumber leaves turning yellow is perform a close inspection of the plant. Make sure to check the stems, tops of the leaves, and bottom of the leaves, especially if the leaves are curling.

Typically, a visual inspection will show you if pests are the problem since yellowing caused by pests indicates quite an infestation.

If you don’t spot any pests, go to the next step.

2. Watch Sunlight Hours

If you planted without paying attention to the sunlight hours your garden receives, now is the time. Watch throughout the day, checking hourly, and make sure those cucumber plants receive at least six hours of direct sunlight per day.

When growing cucumbers under artificial lights, they need 12-16 hours of light since grow lights aren’t as strong as the sun.

3. Consider How Often You Water

One of the problems I had with cucumber plants is that they tend to be like Goldilocks; they like it right in the middle when it comes to watering. They get angry if they don’t receive enough water or if you give too much water.

Typically, if you overwater, the leaves turn yellow, look limp, and may fall off the plant eventually. On the other hand, underwatering may cause yellowing or the leaves to dry up and die.

Think about how often you water. If you water daily, chances are you water too often.

Cucumber plants need one to two inches of water each week, so plan to water twice (or three) times a week. Always account for rainwater in the total tally.

Before watering, put your finger into the soil up to the first knuckle. If the soil feels moist, you don’t need to water.

4. Test the Soil for Nutrients

Cucumbers are heavy feeding plants and require plenty of nutrients. If they lack the minerals and nutrients they need, you’ll quickly know.

One of the telltale signs that your plants have a nutrient deficiency is that the entire plant is pale green compared to a healthy plant. Often times, the bottom leaves turn yellow first, and the overall growth is much slower and stunted.

The best way to determine if your plants have a deficiency is to use a soil test. Your local extension office will have laboratory tests available for a small fee, or use one of the DIY tests at home.

5. Compare the Leaves to Diseases

Lastly, if nothing else seems to be the problem, disease is more than likely the problem. Plenty of diseases – the ones we listed above – cause cucumber leaves to turn yellow.

FAQs about Cucumber Leaves Turning Yellow

Should I Cut Off Yellow Cucumber Leaves?

The first thing you have to do is determine the cause of the yellowing cucumber leaves. If the yellowing is due to environmentally issues or nutrient deficiencies, there is no reason to remove the leaves. However, if the plant has an infestation of pests or a disease, then removing the leaves may help to prevent the spread.

How Often Should Cucumbers Be Watered?

Cucumber plants need one to two inches of water per week. On average, that means you should water every two to three days depending on the temperature and humidity levels outside.

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