Yellow cucumber: 8 reasons why cucumbers turn yellow

Cucumbers are one of the most popular vegetables planted in home gardens and are considered easy to grow. Give them plenty of sunlight, fertile soil, and regular moisture and you can expect a bumper crop of crisp, delicious cucumbers. A cucumber vine that is water stressed, nutrient deficient, or has flowers that aren’t fully pollinated can result in a yellow cucumber or two. If you have a problem with cucumbers turning yellow, read on to learn how to prevent this common complaint. 

Why are my cucumbers yellow

There are many reasons for cucumbers turning yellow. The issue may be weather-related, a sign of a pest or disease, or perhaps it’s a yellow cucumber variety. Below are 8 reasons that may explain your yellow cucumber fruits. 

1) The fruits are over mature

The best quality cucumbers are those that are harvested when slightly immature. At that point the fruits will be crisp, mild-flavored, and top quality. Not sure when your plants will start to produce fruits? Check out the ‘days to maturity’ information listed on the seed packet or in the seed catalog. Most cucumber varieties need 40 to 60 days to go from seed to harvest so start looking for fruits as the expected maturity date nears. 

Overripe cucumbers turn from green to yellow and the flesh softens and becomes mushy and bitter. Never leave over mature cucumber fruits on the plants because they slow down production of new fruits and flowers. Instead, harvest the over mature fruits with your garden snips and either toss them on the compost pile, or if they’re not mushy, cut them in half, scoop out the seeds, and eat the flesh. I often use slightly over ripe cucumbers to make pickles.

2) The variety is a yellow cucumber variety

Another reason you may find a yellow cucumber on your vines is that it’s a yellow-skinned variety. Yes, there are many varieties that produce yellow cucumbers and you don’t have to worry that something is wrong with the plants or the fruits. I love yellow varieties like Boothby Blonde, Itachi, Martini, and Lemon cucumber, which are fun to grow and delicious to eat. Like green cucumbers, yellow varieties should be picked when slightly immature and are best harvested when pale yellow in color. If you wait until they’re bright yellow, they’re likely over mature so keep an eye on the yellow cucumber varieties in your garden. 

3) The plants are water-stressed

Cucumber plants need a lot of water to produce a bumper crop of high-quality fruits. If the plants are water-stressed you may find your cucumbers turning yellow. The best way to prevent this issue is to water deeply several times a week if there has been no rain. If you’re not sure whether you should water, stick a finger two inches into the soil to gauge moisture levels. If the soil is dry two inches down, grab your watering can. 

Conserve soil moisture by mulching around cucumber plants with straw or shredded leaves. Using a mulch lessens drought-stress and also reduces how often you need to irrigate the garden. Less work is always a good thing! When you water, be sure to water the soil, not the plants because splashing water on the foliage of cucumber plants can spread disease. I use a long handled watering wand, directing the flow of water to the base of the plants, but you can also use a soaker hose or drip irritation for a hands-off approach to watering. 

Container grown cucumber plants are more prone to drought-stress than those planted in garden beds. Pay extra attention to watering and expect to grab the watering can daily when the weather is hot and dry. Water potted cucumbers deeply so that water comes out the drainage holes on the bottom of the container. Again, avoid splashing the foliage when you water container cucumbers. 

4) The plants are getting too much water

Just as too little water can result in cucumbers turning yellow, too much can also cause the same result. This is one of the common reasons a cucumber vine would produce a yellow cucumber and is also a reason for cucumber leaves turning yellow. This is where the soil moisture test (remember above where I mentioned sticking your fingers two inches into the soil?) comes in handy. If the weather is cloudy, rainy, or cool the soil won’t dry out as quickly as when it’s hot and sunny so you should water as needed and not on a set schedule.

5) Nutrient deficient vines can cause yellow cucumber fruits

Cucumber plants are heavy feeders and require a regular supply of nutrients to grow and produce lots of cucumbers. If your soil is infertile or you’ve had issues with nutrient deficiency in the past, you may find many of the fruits on your plants are stunted or yellowing. A bumper crop of cucumbers starts with testing the soil every few years to see if your garden is deficient in major nutrients like nitrogen, phosphorus, and potassium. You’ll also learn the soil pH from a soil test and can adjust it so that it’s between 6.0 and 6.5, the ideal range for cucumbers. 

My approach to feeding cucumber plants is simple. I amend my raised beds every spring with two inches of organic matter like compost or aged manure. I also apply a balanced organic vegetable fertilizer at planting time. During the growing season I add a liquid organic fish and seaweed fertilizer to my watering can and feed the plants every 2 to 3 weeks, or as recommended on the fertilizer packaging. 

6) The plants are diseased

There are several common cucumber plant diseases that can affect growth and fruit development, often leading to yellow cucumbers. In my garden the first defence against plant disease is to grow resistant varieties. When reading seed catalogs look for cucumbers like Thunder, Diva, and Burpee Hybrid II which offer resistance to many cucumber diseases. It’s also important to practice crop rotation and plant cucumbers in a different spot next year. Below is more information on three common diseases that can result in yellow cucumbers. 

• Powdery mildew – Powdery mildew is a fungal disease that affects both the top and bottom leaf surface of cucumber plants. It starts off looking like a dusting of white powder but soon the entire leaf surface is coated. It typically shows up in mid to late summer when the weather is hot and dry. Powdery mildew weakens the plant and impacts yield. The fruits ripen prematurely and often turn yellow. 
• Bacterial wilt – Bacterial wilt is easy to spot. The first sign is wilting vines or leaves. Soon, the leaves turn yellow and then brown. As the disease progresses, the fruits are also affected and turn yellow and rot. Bacterial wilt is spread by cucumber beetles and protecting young plants with insect netting can help reduce the occurrence.  
• Leaf spot – There are several fungal diseases that cause leaf spot of cucumber plants. Symptoms start with yellow spots developing on the leaves and as the diseases progresses, affected leaves drop from the plant. Severe cases result in fewer and smaller fruits, with many of the cucumbers turning yellow. 

Other diseases to watch for include cucumber mosaic virus and downy mildew. 

7) Lack of pollination can result in yellow cucumber fruits

Cucumber plants produce separate male and female flowers and for pollination to occur, pollen must be transferred from the male flower to the female flower. Bees do most of the pollinating and each female flower needs 8 to 12 bee visits in order to produce high quality fruits. If pollination doesn’t occur, the female flower, and the tiny fruit beneath it, yellows and falls off. If partial pollination occurs the fruits can become deformed. Those oddly shaped fruits don’t develop well and often turn yellow instead of sizing up. Remove misshapen cucumbers to encourage the plants to keep producing new flowers and fruits. 

Promote good pollination by not spraying any pesticides, even organic ones. Also include flowers and flowering herbs like zinnias, sunflowers, borage, and dill in your cucumber patch to invite pollinators. If you notice the female flowers falling off without producing a fruit or you’re getting a lot of misshapen cucumbers, you can hand pollinate the flowers. Use a cotton swab or small paintbrush to transfer pollen from male flowers to female flowers. Quick and easy! 

8) Insect damage to cucumber plants

There’s no such thing as a pest-free vegetable garden and cucumber lovers are familiar with pests like slugs, aphids, spider mites, and cucumber beetles. While some pest damage is cosmetic, a serious infestation can weaken plants, damage leaves and flowers, and reduce fruit quality. My pest prevention strategies include practicing crop rotation and planting in a site with at least 8 hours of sunlight. I also use science-based companion planting and tuck sweet alyssum, dill, sunflowers, and nasturtiums in and around my cucumber patch to attract beneficial insects. If you want to learn more about science-based companion planting, I highly recommend Jessica’s award-winning book Plant Partners. If an insect infestation is severe, you may wish to use an insecticidal soap. 

For further reading on cucumbers, be sure to check out these in-depth articles:

• When to harvest cucumbers for optimum flavor and quality
• Cucumber plant spacing for high yields in gardens and containers
• Cucumber trellis ideas
• Growing cucumbers in pots
• Identifying and solving common cucumber plant problems

Have you ever found a yellow cucumber on your plants?