Why Is My Cucumber Yellowing? Common Causes & How To Treat Them

Cucumber yellowing is a common problem in the vegetable garden, but it's still disappointing when it happens. Especially because growing cucumbers is typically easy and these garden staples are prolific producers. So if you're wondering, “Why is my cucumber yellow?” Don't worry. We have your answers and solutions right here.

Why Is My Cucumber Yellow?

If the cucumber fruit itself is turning yellow, chances are there is a specific environmental reason behind it. The most common are:

1. Overripeness

One of the more common reasons for cucumber fruit to be yellow is picking it too late. If you allow the cucumber fruit to linger on the plant, it turns yellow and becomes unpalatable. Checking the seed packet can help you know when to harvest cucumbers.

• Pickling cucumbers should be short, firm, and dark green. They are usually about 4 inches (10 cm) long at the time of harvest. If they grow longer, they are overripe and will often begin to yellow.
• Slicing cucumbers are longer than pickling types and grow to 6-12 inches (15-30 cm) in length depending upon the variety. They should be fairly firm and fully green. If the fruit begins to yellow, it is overripe and likely has turned bitter tasting.

2. Not Enough Nitrogen

Studies have shown that having sufficient nitrogen is what fosters the green color of cucumbers. Initially, it was thought that supplementing nitrogen would just result in an explosion of foliage that would shade the fruit resulting in pale cukes, but that wasn’t the case. Of course results varied depending upon the cultivar.

Cucumbers are heavy feeders and should be fed at planting time and again when they begin to flower. At planting time, incorporate compost, well-rotted manure, or a slow release fertilizer into the soil.

When the plants begin to bloom, they need lots of potassium. For optimal fruiting, just as they are beginning to flower, feed plants a liquid fertilizer rich in potassium according to the manufacturer’s instructions. Continue to feed the plants every four weeks until fruit production ceases.

3. Variety

Some cucumber varieties are meant to be yellow, and cucumber yellowing is actually a sign that it's time to harvest. These yellow varieties include:

• Yellow Submarine
• Lemon Yellow
• Salt and Pepper
• Dosakai or Indian
• Kirby
• Mexican
• Diva
• Boothby's Blonde
• Straight 8
• Wautoma
• Jelly Melon

Some of these varieties are delicious eaten fresh, while others like Dosakai make excellent South Indian pickles. Some are similar in shape to standard slicing cukes and others are radically different, like the tiny Mexican cucumber which can be popped right into the mouth and are only about as big as a grape.

Can You Eat a Yellow Cucumber?

Any yellow cucumber varieties listed above are specifically meant to be eaten when yellow and are perfectly edible. However, pickling or slicing cucumbers that are meant to be green are unpalatable if they’ve turned yellow. They tend to be pithy with large seeds and quite bitter. Green cucumbers that have yellowed are also quite fragile and prone to rot rather quickly.

Why Are My Cucumber Leaves Turning Yellow?

Maybe it's not the cucumbers themselves, but the cucumber leaves turning yellow on your plant. If this is the case, the culprit is more likely to be related to pests or disease.

1. Squash Bugs

Squash bugs (Anasa tristis) have mouthparts that pierce the tender foliage to suck out the plant’s sap. Their eggs are oval and gold in color, often laid in a cluster under the leaves. Damage from squash bugs results in small, yellow/green to white areas of stippling on leaves, which may also turn yellow and tattered. Infestation can reduce your cucumber’s production and growth.

The eggs can be removed by hand and disposed of. To thwart adult feeding and egg laying, cover the plants with row covers until bloom time. Remove the covering when your plants begin to flower.

2. Spider Mites

Spider mite damage also results in yellow to white stippling on foliage. These spots may begin to form yellow patches on the upper sides of the leaves while the underside just looks dirty.

Spider mites are tiny and can only be viewed well by using a magnifying glass. When the infestation is large, small webs can be seen on the plant. They suck the chlorophyll out of the leaves which may result in the death of the plant.

Hosing the plant off can dislodge some spider mites. An application of insecticidal soap or neem oil can also reduce their population. Keep the area free of weeds, encourage predatory insects, and keep the plant healthy and stress free. Row covers can be used at the beginning of the season to repel mites.

3. Anthracnose

Anthracnose results in round to irregular spots on leaves that may be yellow, tan or gray. A handful of fungal and bacterial pathogens can cause these symptoms however, so a definitive diagnosis is only possible through lab testing. To combat anthracnose:

• Plant disease resistant cultivars
• Avoid crowding plants
• Water at the base of the plant
• Clean and dispose of any plant detritus
• Plant seeds or transplants a few times during the growing season

4. Downy Mildew

Downy mildew, another fungal disease, has similar symptoms to anthracnose, the difference being the underside of the leaves will have fuzzy gray spots. Fostered by high humidity, cool temperatures and moisture, downy mildew is usually visible on leaves in early to late summer, and can spread as temperatures soar. Treatment is similar to that for anthracnose above.

5. Cucumber mosaic virus (CMV)

This disease presents with yellow or green mosaic patterns. With cucumber mosaic virus, the plants’ leaves may be twisted, stunted or deformed and/or curl up or down. This viral disease is transmitted by insects and survives in perennial weeds. What to do?

• Dispose of infected plants
• Remove weeds
• Control aphids and cucumber beetles that act as vectors
• Plant disease resistant cultivars