Why Your Cucumber Leaves Are Turning Yellow—and How to Fix Them

Cucumbers are a popular crop that produces delicious, crisp fruit for weeks at a time. But if your harvests have dwindled and you notice the leaves look yellow, there may be something wrong with your plants. Yellow leaves indicate that the plant is no longer producing chlorophyll, a condition known as chlorosis.

According to Marta Lynch, farm manager at the Pennsylvania Horticultural Society Green Resource Center, yellow leaves are often a sign that your cucumber plant is in survival mode. "The plant begins to pull valuable nutrients from the leaf to support its healthier parts and then discards the weakened leaf to conserve resources."

There are several reasons this happens, including too much water, drought, nutrient deficiencies, pests, and disease. To help you prevent and treat this condition, we spoke to gardening experts who shared the most common reasons cucumber leaves turn yellow.

Too Much Water

Overwatering cucumber plants can drown the roots, increasing disease risk and decreasing nutrient uptake. "Roots in soggy soil can’t absorb nutrients properly, and prolonged wetness encourages root rot and fungal issues," says Luke Hammond, expert gardener at Seedtime, a leading garden planning and management app. "This lack of oxygen and nutrient uptake shows up first as yellowing leaves." To prevent this issue, let the soil dry slightly between watering and ensure good drainage by planting cucumbers in raised beds or amending the soil with compost. 

Drought

On the other hand, not giving your plants enough water can also cause yellowing leaves. "Drought will decrease nutrient uptake by damaging roots, as well as reduce photosynthesis, which is the plant’s way of producing energy," says Lynch. To address this, she recommends using an organic mulch that can help hold moisture in the soil, as well as considering installing an irrigation system.

Lack of Nutrients

Yellowing leaves can mean your soil is nutrient-deficient. "Nitrogen deficiency causes uniform yellowing of older leaves," says Hammond. "Magnesium or iron deficiency causes yellowing between leaf veins." To address soil issues, Lynch recommends conducting a comprehensive soil test and working with your local extension agent to address soil health issues and discuss fertility programs.

Disease

Diseases caused by bacterial, fungal, or viral pathogens can interfere with photosynthesis or block the flow of water and nutrients, leading to leaf discoloration. According to Hammond, common cucumber diseases that cause yellow leaves include downy mildew, fusarium wilt, and cucumber mosaic virus.

Your treatment plan depends on the type of disease your plant is suffering from, but Hammond recommends starting by removing or destroying infected leaves to slow the spread. To prevent disease from plaguing your cucumber plants, he says to rotate your crops yearly, avoid overhead watering, and choose resistant cucumber varieties.

Pests

Insects, like cucumber beetles, spider mites, and aphids, suck sap from leaves and can transmit diseases, leaving behind yellow stippling or patchy discoloration. "A proactive gardener can help mitigate this risk with good watering practices, biologically active soil, companion planting, and the strategic use of beneficial nematodes," says Hammond. If it's too late, use a blast of water to dislodge pests and regularly apply insecticidal soap to the leaves to treat infestations.

Transplant Shock

If you started cucumbers indoors or purchased plugs from a nursery and then moved them to your garden, transplant shock may cause yellowing leaves. "Newly planted cucumbers may yellow temporarily while adjusting to their new environment," says Hammond. "Transplant shock will more prominently have wilted leaves than just the color variation, but it can manifest itself in so many different ways." To avoid this, gradually introduce the plants to their new surroundings before placing them in the ground, exposing them to increasing increments of sunlight every day for a week.

Age

Yellowing leaves on cucumber plants can be a sign of natural aging. "Older leaves at the bottom naturally yellow and die back as the plant focuses energy on new growth and fruiting," says Hammond. If this is the cause, there isn't much you can do to fix it.