Help! Why Are My Cucumber Plants Turning Yellow?

Cucumbers scream summertime. Chunks of cucumbers fill your salad. Cucumber salads or even cucumber soup, there are so many ways to use these delicious vegetables. The plants typically produce a prolific harvest each year, on tall, sprawling vines. Some cucumbers grow on compact, bushy plants with flat leaves.

Everything seems like it is going great until you see your cucumber plants turning yellow. You start to worry. What in the world could be wrong? Even though you typically can start to pick your first cucumbers as soon as 55 days after planting, there are some problems that plague cucumber plants. It is best not to ignore the problem. Yellow cucumber plants could even lead to a severe problem resulting in the death of your plant. Let’s take a look at what could be the root of the issue. 


Potato Leafhopper

You probably have never heard of potato leafhoppers, but they love to feed on your cucumber plants, sucking the sap from their leaves. These pests inject a toxin into the leaves, as they feed, causing them to turn yellow. As time goes on, the damaged leaves will eventually drop off the plant.


Source: redbubble.com

How do you stop potato leafhoppers? You could spray an insecticide, but you want to be careful spraying chemicals on plants producing your food. The best method is to control all of the weeds in the area around the cucumber plants. You also can use row covers to stop the insects.

Smaller Pests

There is an abundance of little pests that may be sucking sap from the leaves of your cucumber plants. Some common pests are aphids, whiteflies, and spider mites. All of these pests can cause the leaves on your plants to turn yellow and start to curl up.

  • Aphids are tiny, oval-shaped insects that are yellow to green. They prefer to colonize on the undersides of leaves, leaving behind sticky substances that look like black mold.
  • Spider mites cause stippling on the leaves as they suck on the leaves. You can find them on the undersides of the leaves.
  • Whiteflies are tiny, white winged insects on your plants. They hang out on the undersides of leaves and will fly up if you disturbed the leaves.

Source: atrampintheorganicgarden

Luckily, there are ways to treat and stop these annoyances. Many gardeners prefer to use a prepared insecticidal soap, allowing treatments either every week or every other week. Depending on the severity of the infestation, you may have to remove the leaves from the bottom of the plants. Cucumbers can handle a small infestation, but a large scale one will quickly kill a plant. Treatment is needed quickly to save it from an untimely death.

Common Cucumber Plant Diseases

Unfortunately, cucumber plants are susceptible to a variety of bacterial and fungal diseases that can kill your plants quickly. Two of the most common are verticillium wilt and mosaic virus.

  • The Mosaic virus causes the leaves to thicken and become brittle. The plants are stunted with poor yields. This disease is spread from plant to plant by aphids and leafhoppers.
  • Verticillium wilt is a soilborne fungus that leaves light brown streaks on the stem. This disease is common if you plant where potatoes, peppers, eggplant tomatoes once were.

Source: thegardenhelper.com

The bad news is that there is no way to treat these diseases. Gardeners need to remove the infested plants as quickly as possible to prevent the disease from spreading to other plants. The following gardening season, don’t plant any squash or melons in that area because the diseases can live in the soil and infect other crops, even a year later!

There are some other diseases that could infect your cucumber plants.​

  • Do you notice white powdery spots and coating on the leaves? It is caused by powdery mildew, a fungal spore, that develops when humidity is high. Pick off the infested leaves and don’t overwater!
  • If you notice yellow and brown spots on the upper leaf surfaces, downy mildew may be the cause. It is a fungus. You need to improve air circulation and keep your garden free of debris.
  • Fusarium wilt is a fungal disease that causes stunted plants with yellow leaves. It infects the vascular tissues. The spores live in the soil, carried by cucumber beetles. You need to remove and destroy all infected plants because fungicides aren’t effective.

Nitrogen Deficiency

There is another reason that your cucumber plants are turning yellow. It may have a nitrogen deficiency, which leads to pale or yellowing leaves as well as stunted growth. Nitrogen deficiency can kill your plant if the condition is severe.

Nitrogen deficiency is easy to fix. You need to purchase a 6-10-10 fertilizer at the store. Each plant should receive one to two tablespoons of this fertilizer, either when you plant it or when you notice the issue. Gardeners can also add ammonium nitrate, 33-0-0 after the flowers bloom and three weeks later. You don’t want to use too much fertilizer when trying to fix nitrogen deficiency because it stops the plants from producing fruit!

Another easy way to add more nitrogen to your cucumber plants is to add mulch around the base. Grass clippings are free if you have a lawn. As they decompose into the soil, they release nitrogen the soil. While it may stink a bit as the clippings decompose, it is a free source of nitrogen. Everyone loves free!


The first thing that you need to do is determine what is causing your cucumber plants to turn yellow. This step requires a thorough inspection of your plants. Go through your plants and check all of the troubled plants. Remember to turn the leaves over and look at the bottom. The undersides of leaves are where many pests like to hide as they destroy your plants.

If you are unable to find any pests, try to match up the signs with a potential disease. If you quickly identify the problem, you will be able to fix it without losing plants that would’ve given you precious fruits.

Help! Why Are My Cucumber Plants Turning Yellow?
4.3 (85.56%) 18 votes
Tina Martino

My passion is gardening. Along with my husband and children, each year we grow a garden large enough to provide our family of five with over half of our needed produce. Besides vegetables and a small berry patch, I also focus my attention on beautifying our home with strategically placed flowers, herbs, and flowering plants. Gardening is more than just a hobby; it is a way of life.

Click Here to Leave a Comment Below 1 comments
steve wood - July 5, 2020

Can I send you pictures on my cucumbers and zucchini so you can see what I am dealing with? I have seen this in the past and have always had a hard time growing cucumbers but this year its the zucchini as well. Yellowing leaves and some white on them along with weird looking fruit. I believe the white came from the organic rapid grow i sprayed on them. It might just be that I need to over water these things. I am in the inland area of San Diego and its gets warm but I just want to know if its something else like nitrogen issues.


Leave a Reply: