QUESTION: My cucumbers are turning yellow on the vine. What does this mean, and how can I get it to stop?
ANSWER: There are lots of reasons your cucumbers could be turning yellow, with overripeness being the most common. Of course, before trying to diagnose the problem with your cucumbers, make sure you aren’t growing a variety that’s yellow on purpose, like Lemon cucumbers.
Cucumbers Are Too Ripe
If you leave your cucumbers on the vine too long, they’ll start to turn yellow. If this happens to you, that just means you need to learn when to harvest your cucumbers. You should be checking your cucumbers for ripeness at least daily.
It normally takes between 50 and 70 days for a cucumber to grow from a seed to a mature fruit. You can recognize a ripe cucumber by its bright green to dark green skin and firm texture. Cucumbers you plan to slice do best when they’re harvested between seven and nine inches long. Those for pickling should only be allowed to grow to two inches long. For burpless cucumbers, harvest when they’ve reached one and a half inches across.
If your cucumbers are turning yellow, growing puffy or getting wet-looking lesions and withered ends, they’ve developed way past the point of ripeness. Yellowed, overripe cucumbers grow bitter the larger they get. Most of the time, a yellow cucumber is too bitter or mushy to eat. Left on the plant for too long, a yellow cucumber will start to go to seed. Simply throw these cucumbers away.
Infestation by certain types of insects can cause cucumbers to yellow, and some of the insects spread plant diseases, too.
You’ll know aphids are infesting one of your plants if the leaves start to look distorted or withered and lots of tiny insects can be seen on the underside of the foliage. Aphids are responsible for carrying the cucumber mosaic virus from one plant to another as well as damaging the foliage and stressing the plant. You can get rid of aphids by treating with insecticidal soap or a mixture of water, onions, and garlic. Some recipes include hot pepper or citrus as well. Our article All About Aphids, and How to Kill Them has several remedies you can look into.
Cucumber beetles can pass bacterial wilt along to your plants or, like aphids, spread the cucumber mosaic virus. You can keep them off your plants by setting up floating row covers at the beginning of the season. When the plants start to develop flowers, you’ll need to remove the row covers so the flowers can be pollinated.
Once row covers have been removed, you can fight the cucumber beetle population in your garden with once-weekly or twice-weekly applications of insecticidal soap as well as pulling the beetles off yourself. If leaves are too badly damaged by cucumber beetles, you may need to remove them.
If cucumber beetles have been a problem in your garden, you’ll need to rotate your crops every two years to overcome them. This is because the bugs can spend the winter in your soil and return the following season to strike again.
Here’s our article on 13 Natural Ways to Fight Cucumber Beetles.
These insects usually do their worst to potato crops, but they can cause some damage to the cucumbers you’ve planted as well. A substance potato leafhoppers emit is poisonous to cucumber plants and causes their leaves to turn yellow and fall off the plant.
Keep potato leafhoppers at bay by keeping plenty of space between your plants and weeding carefully. You can also treat your plants for potato leafhoppers with diatomaceous earth or insecticidal soap. Just be sure to apply your treatments to both the top and bottom leaves of the plants.
Southern Corn Rootworm
“Southern corn rootworm” is the name for the larval stage of spotted cucumber beetles. These bugs live in the soil and cause yellow leaves by chomping straight through plant stems from the surface of the soil. You may also notice slower growth than usual from afflicted plants.
If your garden has southern corn rootworms, you’ll need to pull up and discard any plants that show signs of infestation. Wherever you see affected foliage, trim it off the plant with disinfected gardening shears.
You should also turn the soil over frequently, and some gardeners recommend paying special attention to aerating the soil around the base of your cucumber plants. Loosening the soil is especially helpful if you’ve struggled with spotted cucumber beetles in the past.
Lack of Nutrition
Cucumber plants need a lot of nutrition to make flowers and fruit, so if they don’t get enough, the result can be yellowed cucumbers. Anything that causes malnourishment in a plant can be to blame. Your soil may just be poor and not contain what your plants need to thrive. Or maybe your soil started out fine, but you’ve been growing cucumbers in it for years. Cucumbers that are yellowing due to a lack of nutrition may also be smaller than normal.
For healthy cucumber plants, your soil should offer a blend of nitrogen, phosphorus, and potassium. If these nutrients are not available in the soil to start with, you may need to use a fertilizer to make the soil more fertile.
You’ll notice that fertilizers are sold marked with three numbers separated with hyphens, such as 10-8-10. These numbers represent how much of the three nutrients (nitrogen, phosphorus, and potassium—in that order) the fertilizer contains.
Choose a fertilizer that has slightly more nitrogen than phosphorus or potassium if you are using it to combat yellow cucumbers, like 10-7-7 or 7-5-5.
You can also supplement the fertilizer by amending your soil with compost before planting your cucumbers. However, compost is highest in potassium, unless it contains lots of a nitrogen-heavy ingredient, like animal manure.
Even with proper fertilization, you’ll need to rotate your crops instead of planting cucumbers in the same part of your garden year in and year out. For best results, plan for a three- to four-year crop rotation schedule. This article on crop rotation has more information you can delve into.
Lack of Pollination
Some cucumbers turn yellow and drop from the plant if the attached flower does not get pollinated well. There are a few things you can do to help encourage healthy pollination.
Attract pollinating insects and hummingbirds to your garden with plants they like, feeders, or homes for bees. Be aware that using pesticides or insecticides in your garden will get rid of beneficial pollinators, too. Floating row covers should be removed when flowers appear so the insects can reach the blossoms. If all else fails, you can gently pollinate flowers yourself with a paintbrush or cotton swab.
Lack of Sunlight
If your plants aren’t getting sunlight, they can’t create the chlorophyll that keeps leaves green. As a result, you might notice yellow foliage along with failure to thrive or produce flowers and cucumbers. Make sure your cucumbers are getting sufficient sunshine: most types need at least six hours per day.
Lack of Water or Too Much Water
Cucumbers can turn yellow if their shallow roots get waterlogged, if you’re going too long between watering sessions and they’re drying out, or if their moisture has just been inconsistent. Containers are especially prone to getting too dry in the sun,
The best guideline is to water your cucumber plants once a week only whenever it’s dry. You can check to see whether it’s time to water your cucumbers by inserting your finger into the soil an inch deep. Does the soil cling to your finger, or do you feel it’s moist? If so, it’s not yet time to water your cucumber plants.
Using compost or mulch in your garden is a wonderful way to make moisture more available for your plants. Compost also improves the texture of the soil, which keeps it from getting oversaturated as easily.
Many different plant diseases can result in your cucumbers turning yellow. You’ll need to do a visual inspection of your cucumber plants for other symptoms, then compare them to the information below to find out exactly what the problem is in your cucumber patch.
Cucumber Mosaic Virus
Near the start of this article, we discussed treating for aphids. If you have cucumber mosaic virus, it’s most likely been transmitted to your plants by these tiny insects. You can get substantial results by planting lots of flowers close to your cucumbers, which will attract predators of the aphids. Beetles can be a potential cause of cucumber mosaic virus, too.
If the yellow areas on your cucumbers are tinged with white, you should suspect cucumber mosaic virus. You’ll see this discoloration on the leaves, too. If your plants are infected with cucumber mosaic virus, you really have no choice but to clear the cucumber plants out and discard them. However, make sure not to put them (or any plants you suspect are diseased) into your compost pile.
Some of the best defenses against cucumber mosaic virus are simply growing healthy plants and rotating crops so cucumbers aren’t constantly grown in the same spot. You can also use floating row covers and other products that keep insects off plants to reduce the likelihood of infection.
Fungal Disease or Powdery Mildew
Powdery mildew is the common name for a fungus that causes yellowed cucumbers along with limited chlorophyll for the whole plant. This is often the result of water splashing onto the leaves of the plants when they are watered. Other types of fungus can cause disease for the same reason. Be careful to aim the water at the base of the plants. Not only can excess moisture on their foliage cause disease, they also can’t absorb water anywhere but through their roots.
If the excess moisture in your cucumber patch is caused by a problem with soil drainage or air circulation, these may also need to be addressed for you to beat fungal disease or powdery mildew. Growing cucumbers vertically can be a solution to cramped spaces that cause air circulation problems. Cucumber plants should have 16 inches of space between them.
In this article, we’ve given you the other symptoms to look for in order to diagnose why your cucumbers are turning yellow. Where possible, we’ve also provided remedies you can use against this problem. Let us know in the comments what has worked for you in the past or share your experiences with yellowing cucumbers.