Why your cucumber leaves are turning yellow—and what to do about it

Yellow leaves can be a sign of several problems.

Cucumbers are one of the easiest vegetables for beginning gardeners to grow, and they even tell you when something’s not quite right. If your cucumber plant has yellowing leaves, it’s a common problem but one that signals you need to take action before your crop takes an unexpected turn. Yellow leaves are a sign of several issues that can occur when growing cucumbers, from watering issues to too much sun. Here’s how to tell what’s causing your cucumber plant’s leaves to turn yellow and what to do about it.

Overwatering

Cucumbers do need a lot of water to thrive, 1 inch per week. Problems with watering can look similar in a cucumber plant. Leaves may wilt and turn yellow if both overwatered and underwatered. There are a few more signs that can help you determine whether too much or too little water is the cause. 

If a cucumber plant is getting too much water, its leaves may wilt and turn yellow, but they will also feel soft and limp and may eventually drop. Watering won’t correct wilted leaves, and the soil may be soggy, which can lead to root rot. Roots may turn brown or black and have a foul odor. Reduce watering frequency, and let the top few inches of soil dry out before watering again. Make sure the soil is well-draining.

Underwatering

Too little water can also cause cucumber leaves to wilt and turn yellow, but the leaves may turn brown at the edges and feel crisp and dry. Aim to give cucumber plants an inch of water each week from irrigation or rainfall, and water when the top few inches of soil feel dry. Mulching can help the plant’s shallow roots retain moisture.

Temperature And Humidity

Cucumbers like warm temperatures and do best in 75ºF to 85ºF. They don’t tolerate frost. Sudden temperature changes and cooler nighttime temperatures can cause leaves to turn yellow. Acclimate plants to outdoor temperatures before planting them in the spring, and cover the plants during cold spells. During very hot weather, shading the plant can protect it from too much sun.

Cucumbers like higher humidity levels, around 60 to 70 percent, but high humidity can cause leaves to yellow when combined with periods of extended moisture on the leaves. This combination can lead to fungal diseases and other issues that cause yellowing leaves.

Nutrient Deficiencies

If water and temperature aren’t to blame for your cucumber plant’s yellowing leaves, missing nutrients could be the cause. To fulfill your plant’s needs, choose an appropriate fertilizer with the needed nutrients, and make sure the soil pH is slightly acidic (6.0-6.5). Which nutrient your plant is deficient in can be determined by a few factors:

• Too little nitrogen causes yellowing that starts at the bottom of the plant with older leaves and works its way up. The plant may also have stunted growth and reduced fruit size. Treat with a nitrogen-rich fertilizer like fish emulsion or a water-soluble fertilizer.
• Potassium deficiency causes yellowing and scorching along leaf edges, weak stems, and interveinal chlorosis, a yellowing between the leaf veins. Amend the soil with compost or a potassium-rich fertilizer.
• Lack of magnesium can cause older leaves to yellow and progress to younger leaves, as well as interveinal chlorosis. Apply a balanced fertilizer that contains magnesium.
• Interveinal chlorosis and yellowing in new leaves can indicate an iron deficiency. Yellowing leaves may eventually turn brown and die. Apply a fertilizer with added iron.

Too Much Sunlight

Cucumbers need at least six hours of sunlight each day. If the plant gets too much sun, its leaves can develop crisp, brown edges and eventually yellow and die. In hot weather, cucumber plants benefit from some shade during the warmest part of the day. Use a shade cloth or even an umbrella to protect them from too much sun since it can affect the flavor of your crop.

Diseases

Disease could be the culprit of a cucumber plant’s yellowing leaves. Rotate crops every two or three years and water the plants at soil level rather than overhead to avoid getting the leaves wet.

Anthracnose

Anthracnose is a fungal disease that flourishes in warm, humid environments. In cucumbers, it begins as small pale yellow spots on the leaves that eventually enlarge and turn dark brown. The centers of the leaves may eventually develop holes and cracks and become jagged looking. Avoid getting leaves wet when watering. Treat with a fungicide.

Cucumber Mosaic Virus

This virus shows up as discolored leaves with a green and yellow mosaic pattern, yellow streaks or spots, interveinal chlorosis, or deformed leaves. It can be caused by pests, high temperatures, and mineral deficiencies or excess. There is no treatment, so discard a diseased plant as soon as symptoms appear.

Angular Leaf Spot

Leaves affected by this bacterial disease develop angular tan or brown spots with a yellow halo. The spots may eventually dry out, leaving holes behind. Choose resistant varieties and water at the base of the plant to avoid getting the leaves wet. Use a fungicide for treatment.

Pests

Aphids, squash bugs, and spider mites can suck a cucumber plant’s sap and cause the leaves to yellow, brown, or curl. Aphids cluster on the undersides of leaves, and spider mites create webbing under the leaves. Other pests like cucumber beetles feed on the leaves, causing yellowing and holes. To get rid of pests, remove them with a strong spray of water from the garden hose, treat with neem oil or insecticidal soap, or remove the pests by hand.

Read the original article on Southern Living