Why Are My Cucumbers Turning Yellow?

Cucumbers are easy to grow and delicious to eat.

And they’re one of the most popular plants grown in home vegetable gardens.

But sometimes, you don’t get what you expect.

Instead of the dark green color that everyone knows, some of your cucumbers come out differently.

If you’re left wondering ‘why are my cucumbers turning yellow?’ we’ve got the answers for you.

Let’s dive in.

Over-Ripening

overripe cucumber

Overripe cucumber by Aravind Sivaraj, CC BY-SA 3.0

If you want to stop your cucumbers turning yellow then one of the most important gardening tips is to make sure you pick them at the right time.

You see, if you leave it too long then they become over-ripe. At this point, they usually taste bitter and are unfit for eating. So the fruit will go to waste.

Cucumbers are fast growers and are usually ripe after about 50 days or so. They should be firm to touch and medium to dark green in color.

It’s better to pick them early. This means they might not reach their full potential size. But you will have a fresh, tasty, and crunchy cucumber to enjoy.

If you’re growing slicing cucumbers, then picking them when they’re between 7-9 inches is recommended. With the majority of growers choosing to pick them by the time they get to 8 inches in length.

Pickling cucumbers are usually picked when they’re much shorter, just a couple of inches or so. Making them easy to pack in the jars.

Nutrient Deficiencies

Fertilizer added to small cucumber plant

A lack of essential nutrients is another common cause of cucumbers turning yellow. And if the yellowing is combined with stunted growth, then you can confidently identify this as the cause.

The most common nutrient deficiency that has this effect is nitrogen deficiency.

You can treat the problem by using NPK fertilizer. Cucumbers usually need more phosphorus and potassium than nitrogen. And often do well with a ratio similar to 5-10-10. But if your soil is nitrogen deficient you can try a balanced NPK fertilizer like 10-10-10.

Be careful adding too much nitrogen though. It can lead to vine growth at the expense of cucumber growth.

Another way to avoid this problem is to practice crop rotation in larger outdoor gardens.

One of the problems of growing cucumbers in the same area of your garden year after year is that the nutrients they need can become depleted from the soil.

Rotating plants with different nutrient requirements around pre-arranged plots in your garden is a time tested way to prevent soil deficiencies. And it has the added benefit of helping with pest and disease control.

Nutrient depletion is also common when growing in containers and not adequately fertilizing the soil.

Yellow Cucumber Varieties

Lemon cucumber

Lemon cucumber by Jamain, CC BY-SA 3.0

Although long, slender, dark green cucumbers are common, not all types of cucumbers look like this.

If your cucumbers look different it may be that you’re growing one of the varieties that are yellow.

Lemon cucumbers and dosakai cucumbers are yellow and round. Another common variety is the Chinese yellow cucumber, which is elongated, fat, and similar in shape to a regular cucumber.

Lack Of Water

Watering can prepared to water cucumber plants

Cucumbers need a lot of water as they grow. And if you’re not giving them enough you might see some of the cucumbers turn yellow.

Make sure your plants get 1-2 inches of water a week. Cucumbers do better with occasional, but deeper, watering. So aim to water them 1-2 times per week.

How do you know when they need to be watered?

Feel the top inch of soil with your fingers. When it feels dry it’s time to water them again.

The majority of the roots are in the top 8 inches of soil. So watering close to the base of the plant will make sure they get what they need.

But, you also have to be careful not to overwater cucumber plants. They don’t like being sat in soggy soil. It prevents them from uptaking an adequate amount of oxygen which affects their growth. And the wet soil encourages the growth of fungal infections such as root rot.

Plant Diseases

Plant disease is another cause of cucumbers turning yellow.

Unfortunately, a variety of fungi and bacteria can affect your plants. Leading to problems with the fruit, wilting of the plant, and causing them to die.

Worse still, many of these diseases have no effective treatment. And quick action is needed to remove and destroy the plants to stop the infection from spreading.

But knowing the symptoms will help you with early identification, increasing your chances of saving your plants.

Cucumber Mosaic Virus

cucumber mosaic virus

Cucumber mosaic virus was first discovered on cucumber plants hence its name. But it also infects other cucurbits such as squash.

It’s spread by insects, with aphids being the main carrier. But other common pests, such as cucumber beetles, can transfer it when they feed on the leaves of your plants.

Common symptoms include wrinkled leaves with yellow spots. And problems with fruit development. Often leaving them short and stubby. And with white or yellow mottling.

The cucumbers produced by a plant infected with cucumber mosaic virus are no good to eat. So you’ll have to throw them away.

As there’s no cure, the best you can do is to prevent it in the first place. Or at the very least, stop it from spreading to other cucumber plants.

Take a closer look at your plants to see if you can find the insects causing the problem.

Aphids on a green leaf

Aphids (Aphidoidea) on a leaf

Aphids are very small, and green or yellow. You’ll find them on the underside of the cucumber leaves. They leave a sticky black substance known as honeydew that shows you where they’ve been.

Cucumber beetles are easy to spot against the green background of a leaf. They’re bright yellow in color and have black markings which are either striped or spotted. They grow to about a ¼ of an inch long.

There are a number of things you can do:

Floating row covers prevent insects from getting to your cucumber plants. But remember to remove them when the flowers bloom so they can be pollinated.

Other methods of prevention include spraying the leaves with insecticidal soap. And neem oil can work to treat aphid infestations.

If you have a problem with cucumber beetles, removing weeds and spreading a layer of mulch around your plants can reduce their numbers.

You can also try cucumber beetle traps. These consist of bags containing a chemical attractant and sticky paper to trap the beetles as they investigate. The beetles are drawn to the traps and not to your cucumbers when you hang them near a cucumber plant.

Other Common Diseases

Other diseases that affect cucumber plants include powdery mildew and bacterial wilt. With both of these, you’ll see your cucumber leaves turning yellow and brown. With white patches of fungus developing when a plant is infected by powdery mildew.

The growth of the cucumber fruit can be affected. But while changes on the leaves are highly visible, discoloration of the fruit itself is less common.

What To Do With Yellow Cucumbers

Compost bin

Compost bin containing vegetable and garden waste

So, you’ve got some yellow cucumbers growing on your plant. Is there anything else you can do with them except throw them away?

If you don’t like things going to waste, then there are a few uses you can put them to.

Compost

You might not want to eat your yellow and bitter cucumbers. But you can still recycle them in your compost bin.

They’re a good source of essential nutrients such as nitrogen. And can be used to help other plants in your garden get the nourishment they need to grow.

Just make sure they don’t have a disease first. You should throw away diseased cucumbers.

The Seeds

Over-ripe yellow or orange cucumbers are actually fully mature fruit. This means that unlike the green ones that you pick to eat, they contain fully developed seeds that you can keep and use next year to grow more plants.

Because we harvest green cucumbers prematurely, the seeds they contain are inadequate for planting.

Pickles & Relish

Even if your yellow cucumbers taste bitter you can still use them for making pickles or relish. Vinegar and seasoning can hide the bitter flavor and make them into an enjoyable side dish.

Featured image by Thamizhpparithi Maari, CC BY-SA 4.0

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