Growing cucumbers in the vegetable garden feels like a pretty straightforward project—until you see your cucumber plant's leaves start to turn yellow. It's one of several common problems cucumber growers face.
Don't confuse yellowing cucumber leaves with the actual fruit ripening to yellow or getting normal yellow spots. Yellowing leaves are an early sign to take steps to prevent the underlying problem from getting worse, spreading, and undermining a bountiful harvest.
Here are six common reasons cucumber leaves turn yellow, how to discover the cause, and fix the problem.
Over or Underwatering
Overwatered cucumber plants are vulnerable to root rot, of which a primary symptom is top leaves wilting, turning yellow, and dropping off. It moves down the vines and defoliates the plant which eventually dies.
Underwatering cucumbers also results in yellow leaves. When plants get too dry, leaves curl, turn brown at the edges and fade from green to yellow, dry up, and fall off.
Cucumbers are 96% percent water, the highest water content of any vegetable, so they need lots of water to survive.
Give cucumber plants an inch of water each week, irrigating at soil level. Choose a planting location with loose, well draining soil and work in compost before sowing seed.
Incorrect Sunlight
Too much direct sunlight causes leaf burn and brown crinkly leaf edges on cucumbers. Eventually leaves turn yellow and die exposing fruits and reducing flavor and yield. The leaves are important for protecting the developing fruit from overexposure.
Cucumber plants thrive in heat and sunlight, so you have to give them enough sun but not too much. Plants need a minimum of six hours of bright, direct sunlight daily and temperatures between 65 and 85°F. If your garden receives extended periods with temperatures above 85°F, reduce the chance of sunburn by providing some afternoon shade.
Trellising is a practical and space-saving way to grow cucumbers while providing a good balance of direct sun for the vines and healthy foliage to shade fruits.
Nutrient Deficiency
Inadequate amounts of nutrients and micronutrients cause cucumber leaves to yellow. A few clues tell which nutrient is lacking, but generally cucumbers need high amounts of both phosphorous and potassium. An NPK fertilizer such as a 2-4-6 works best for these heavy feeders, which benefit from an application of liquid fertilizer every two weeks.
Here are a few signs to help you identify the nutrient lacking in your cucumber plants.
- Nitrogen deficiency: On an immature plant, vines grow slowly and other leaves uniformly turn yellow and drop. (This is most common on young plants.)
- Iron deficiency: New leaves become chlorotic turning a pale yellow-green, then completely yellow except for the veins which remain green. Apply a fertilizer with added iron.
- Phosphorous deficiency: Plants are stunted with small gray-green leaves. The lowest leaf on a shoot turns bright yellow while the leaf just above retains its green color.
- Potassium deficiency: Older leaves yellow and scorched along the edges moving inward toward the center of the leaf which dies and falls off.
Tip
Cucumbers use the most nitrogen during early growth, so prepare the soil before planting. Work in aged compost or add a balanced NPK fertilizer. If signs of nitrogen deficiency appear after planting, feed the plant an all-purpose balanced fertilizer or treat foliage with a liquid spray of kelp or fish emulsion.
Insect Pests
Cucumber vines rarely succumb to insect infestations, however sap sucking pests do cause leaves to turn yellow and die off and also spread disease.
- Aphids multiply quickly so it's important to knock them down early. Look for these pests on the undersides of leaves and knock them off with a strong spray from a garden hose. Use insecticidal soap for serious infestations.
Tip
The presence of ants are a clue your cucumber plant may have aphids. The pests leave behind a substance called honeydew that attracts ants.
- Spider mites also are tiny sap-sucking pests that cause yellow mottling on cucumber leaves. Look for webbing on the undersides of leaves. The mites seldom move, but gently shaking the vine will cause the small red bugs to scurry, which helps you identify them.
- Cucumber beetles are a particular problem for cucumbers. Although they damage leaves by chewing, the worst damage happens when the disease they carry spreads to other plants.
Cucumber Plant Diseases
There are a few plant diseases that can cause the yellowing of cucumber leaves.
- Cucumber mosaic virus turns cucumber leaves a mottled yellow, green, and white. Plants and fruits are stunted and fruit is bitter. Purchase virus-free seeds and seedlings and keep the planting area weed-free. Pull infected plants and put them in the trash.
- Angular leaf spot creates water-soaked spots on leaves with a yellow halo that eventually fall out, making leaves look tattered. Treat it with inorganic fungicides early in the season and aim to prevent it by using drip irrigation and rotating melons and cucumbers every two years.
- Anthracnose causes dark leaf spots with yellow halos and the leaves to eventually fall off. Manage it with repeated applications of fungicide.
FAQ
How do you fix cucumber leaves that are turning yellow?
To fix cucumber leaves that are turning yellow, you may have to water less (or more) often, provide supplemental nutrients, or treat a pest or disease. It depends on the cause. First check to make sure the plant is receiving the right amount of water and light, since that is the most common problem.
What do the leaves on an overwatered cucumber plant look like?
Overwatered cucumber leaves are yellow or brown and wilted.
Should you cut the yellow leaves off of cucumber plants?
Yes, you should cut yellow leaves off a cucumber plant. Removing yellow leaves allows the plant to put energy into creating new healthy growth. Though if the cucumber has mosaic virus, the only option is to pull the plant and trash it.
