6 Reasons Why Cucumber Leaves Turn Yellow (And 6 Solutions)

Growing your own cucumbers at home is highly rewarding. Homegrown cucumber tastes much better than those you buy at the store. However, sometimes gardeners will face problems with their cucumber plants and one of these is the leaves turning yellow.

There are a variety of reasons that the leaves of your cucumber are turning yellow. These include not enough moisture, a lack of nutrients, an insect attack, or disease. You want to fix these problems as quickly as you can so that your plant keeps producing more of its lovely fruits.

Here are six possible reasons that cucumber leaves are turning yellow and how you can fix them.

Not Getting Enough Sun

Cucumber plants need to be exposed to at least 6 to 8 hours of sunlight on a daily basis. This enables plants to use the energy from the sun for photosynthesis and to produce chlorophyll. It’s this chlorophyll that is responsible for the green color of the leaves and the overall health of the plant.

Therefore, if a cucumber plant is unable to produce enough chlorophyll to keep the leaves green, it will eventually die.

How To Fix

It’s not recommended that you move cucumber plants that are already growing in the ground. If the cucumbers simply aren’t getting enough sunlight, you might want to consider trimming back any plant nearby that may be shading the cucumbers.

Otherwise, you might have to start again with some new plants and grow them in a sunnier spot in your garden.

Not Getting Enough Water

You might be aware that cucumbers are quite thirsty plants and need around 1 to 2 inches of water every week. Therefore, if your area hasn’t been receiving enough rainfall and you have forgotten to water your plants regularly, this could be the reason that the leaves are turning yellow on your cucumber.

How To Fix

Check the moisture level of the soil around the cucumber plants. If the top inch of soil feels dry, it’s time to give your plants a good drink. It’s important to direct the water at the base of the plant so that it can soak into the soil.

In periods of hot, dry weather, it may be necessary to check your plants on a daily basis to ensure that they’re getting the moisture that they need.

Waterlogged Soil

Too much water and waterlogged soils can also be a problem for cucumber plants. While they need lots of water to thrive, they don’t appreciate their roots sitting in water. Therefore, the soil that you’re growing your cucumbers in needs to be free-draining.

When the soil is constantly waterlogged, it deprives the roots of oxygen because the air spaces in the soil are filled with water. Ultimately, this will suffocate your plant and the first sign of trouble is the yellowing of the leaves.

How To Fix

If your plants are growing in waterlogged soil, there’s not very much that you are able to do because these plants don’t really like to be moved. What you could consider is gently removing some of the soggy soil from around the plant without disturbing the roots.

Replace this with either coarse sand or some good compost in order to improve drainage. Let the top 2 inches of the soil dry out before you give your cucumbers more water.

Nutrient-Deficiency

As well as needing adequate amounts of water, your cucumbers also need a variety of nutrients to enable them to thrive. Therefore, if the leaves of your cucumber are turning yellow, the plant could be suffering from a nitrogen deficiency.

Nitrogen is one the three major essential nutrients and is responsible for the green growth in all plants. In addition to nitrogen, cucumbers also need phosphorus for strong and healthy root growth and potassium to encourage fruiting.

Apart from a major nutrient deficiency, the cucumber plants could also be suffering from deficiencies in minor trace elements. For example, if the new leaves on your plant are yellow but have green veins, the plant could be suffering from an iron deficiency.

On the other hand, if you see the older leaves turning yellow, but their veins are still green, the plant could be suffering from a zinc deficiency.

How To Fix

The quickest way to fix a nutrient deficiency in cucumber plants is to apply a liquid fertilizer. Select a liquid fertilizer that is specifically designed for fruiting plants and apply this as per the instructions on the pack.

Continue to feed the cucumber plants every two or three weeks with the liquid fertilizer and you should see a vast improvement in no time.

Additionally, add a layer of aged compost around the base of the plant as this will add valuable nutrients to the soil as it breaks down.

For an iron deficiency, you can get liquid iron at your local garden center and apply this to the foliage using a spray bottle. A zinc deficiency can be rectified by giving the plant a solution of zinc sulfate or by using liquid kelp or seaweed concentrate to water your plants.

Plant Disease

There are various diseases that can infect cucumber plants and cause the leaves to go yellow. We’ll look at these individually so that you can understand the best way to treat them.

Cucumber Mosaic Virus

This causes the leaves to display yellow spots on the leaves in a mosaic pattern. These spots eventually turn brown and die, leaving holes in the leaves.

How To Fix

Unfortunately, there’s no treatment for cucumber mosaic virus. You must dig the plants up and dispose of them in the garbage. This needs to be done promptly so that the disease doesn’t spread to other healthy plants in your garden.

You also need to be aware that this virus can live in the soil for at least one year. Therefore, refrain from growing cucumbers in the same spot the following year so that you don’t continue the life cycle of the virus.

Downy Mildew

Downy mildew also causes yellow spots on the leaves that will eventually turn brown. You’ll also notice a gray fuzzy substance on the underside of the leaves.

How To Fix

Because downy mildew is a fungal disease, it can be treated with a regular liquid fungicide. This spray should be applied to your plants quickly so that the disease doesn’t spread.

A second or third application of fungicide may be necessary to eliminate the disease entirely.

Fusarium Wilt

This is another fungal disease that causes yellowing of the leaves as well as dark spots on the lower parts of the stems. The fungal spores responsible for this disease can survive in the soil for quite a long time.

Once the cucumber plant has been infected with this disease, there’s nothing you are able to do to save it. However, it’s important to remove the infected plant as soon as possible and dispose of it in the garbage.

Sap-Sucking Insects Infestation

Another problem that could be causing the cucumber leaves to turn yellow is if the plant has been infested with sap-sucking insects. These insects suck the sap from the leaves, and the leaves will turn yellow and eventually die.

Let’s have a look at the different sap-sucking insects and how you can get rid of them.

Spider Mites

Spider mites are tiny and not easy to see with the naked eye. However, you can identify an infestation by looking for their tiny silvery webs on the undersides of the leaves.

How To Fix

Fortunately, these pests are fairly easy to get rid of. All you have to do is spray the plant with a mixture of either neem oil or insecticidal soap and water. Be sure to spray both the tops and undersides of the leaves and reapply if your plant has a heavy infestation.

Aphids

These tiny green sap suckers will only become a problem if you have a very heavy infestation and there are no ladybirds or lacewings in your garden. The larvae of ladybirds and lacewings feed on the aphids, so they should help to curtail the problem.

However, you can treat an aphid infestation in the same manner that you treat spider mites.

Whiteflies

These annoying pests can become a real problem in your garden if you don’t deal with them promptly. This is because they multiply rapidly, and because they’re flying insects, common sprays such as insecticidal soap won’t always get the entire population.

One thing that you should do is get some sticky insect tape from your local garden center. Hang this near the cucumber plants and then blast the whiteflies off with a spray of water. They’ll fly into the tape and get stuck.

Cucumber Beetle

This pest will destroy cucumber plants if left unchecked. It eats the leaves, leaving behind holes that turn the leaf yellow before it drops off the plant.

These beetles can be picked off your plant by hand and deposited into a jar of soapy water to kill them. To limit the movement of these beetles, you should place a thick layer of straw mulch around your plants.