5+ Causes of Cucumber Leaves Turning Yellow

The lush green leaves and sizeable yields indicate that your Cucumbers are thriving, but keep an eye out for suspicious yellowing leaves.

Cucumbers make one of the quickest-growing crops, as they are ready for harvest within 50 to 70 days of sowing seeds.

Read on to find out what may cause yellowing Cucumber leaves and ways to treat them on time.

Is it Normal for Cucumber Leaves to Turn Yellow?

You should know that seeing yellow leaves is quite normal.

The Cucumber leaves turning yellow with brown spots indicate that they are decaying, which happens once they mature, especially the bottom leaves.

It is prevalent at the end of the growing season when the Cucumber plant demands the pruning of decayed foliage to conserve energy for long winter hibernation.

However, any yellowing seen on the leaves early in the growing season or anywhere between indicates a severe problem. In fact, it may not be expected at all.

Why are my Cucumber Leaves Turning Yellow? (Causes & Solutions)

The primary reasons why Cucumber leaves would prematurely turn yellow is due to deficiencies in the soil and light, deadly horticultural diseases and pests, and overly moist conditions.

Learn the possible causes in detail and fix them discretely!

1. Inadequate Lighting

The Cucumber is a fruit-bearing plant that requires full sunlight throughout the growing season to maintain healthy root and stem growth.

These plants love the warmth and light, requiring at least 6 to 8 hours of sunlight daily.

Here is a quick overview of the importance of lighting duration for plants. 

Therefore, robbing them of precious sunlight will prevent healthy fruit growth and green leaves.

Moreover, lack of chlorophyll is the primary culprit for yellowing Cucumber leaves.

However, leaving them high and dry in the scorching sun will burn the foliage with a visible hollow surface.

Solutions

• Plant the Cucumber rows in the south-facing garden so that each sapling can get ample sunlight throughout the day.
• Avoid planting them close to trees and tall plants, which may provide shade throughout the day.
• Build an arbor or pergola around the Cucumber rows to ensure they get afternoon shade and prevent burn.
• Plant them in mid-spring or early summer when the sunlight is at the fullest. The University of Maryland suggests providing 8 to 10 hours of sunlight per day.
• Consider moving your Cucumber indoors under artificial LED light for at least 12 hours each day in areas with less sunlight.

2. Overwatering the Plant

Cucumber plants need consistent watering of about 1 to 2 inches a week and nothing more.

Moreover, the soil should be well-drained to exert excess water into the ground.

Therefore, overwatering Cucumber plants may lead to moisture stress, which is indicated by yellowing foliage.

The overwatered Cucumber plant looks like the wilted, yellow, or brown plant. It will choke in as the roots are deprived of oxygen and nutrients.

The leaves will be robbed of nutrients and oxygen required for food production, leading to a yellowing and wilting appearance.

Both inconsistent and overwatering can lead to choked roots and sometimes root rot due to excess moisture.

Solutions

• Start by following a watering schedule for your garden-grown Cucumber plant.
• Introduce drip irrigation, where drops of water trickle on the soil consistently to control water intake.

• Consider growing Cucumber in a raised bed with well-drained soil to avoid poor irrigation.
• Use a soil-moisture meter every week or before watering (Anything above 6 indicates an overwatered plant).
• Cut watering in monsoon when the rainfall is prevalent or add a canopy to prevent rainwater from seeping into the soil.

3. Nutrient Deficiency

Cucumber plants deprived of nutrients, especially iron or iron sulfate, will exhibit sickly-looking structures with yellowing leaves.

You can tell your plant suffers from nutrient deficiency when the older leaves stay green, but the young leaves change color.

Similarly, nitrogen, calcium, and magnesium deficiency due to soil salinity, waterlogged soil, and a high supply of potassium or ammonium from over-fertilization may also cause yellowing leaves.

The young leaves may look distorted and cup downwards or produce a light tan burn inside the yellow area.

Here is how each nutrient plays a role in plants growth;

Solutions

• Introduce appropriate fertilizer for Cucumber plants such as Miracle-Gro 2000422 Plant Food or Jobe’s 09026NA Plant Food Vegetables & Tomato.
• Use a fertilizer with a ratio of 5-10-10 to ensure optimal nitrogen intake without overfeeding.
• Spray liquid iron on the foliage or use chelated iron in granular form on iron deficient plants.
• Avoid using ammonium-based fertilizer such as chemical plant food.
• Spray soluble magnesium nitrate or Epsom salt to the magnesium deficient plant once or twice until the condition improves.
• You can also use coffee grounds or organic compost to avoid nitrogen deficiency in plants.

Avoid using excessive nitrogen-based fertilizers as it may result in excessive foliage and no fruits at all.

4. Poor Soil Condition

Cucumber plants thrive in loamy, well-draining soil as it promotes root development and controls water uptake.

In an ideal soil condition, the plant will grow 36 to 48 inches of roots; therefore, you should use the correct potting mix for garden and indoor-grown Cucumber plants.

Solutions

• Grow Cucumbers in a raised garden bed with a hand-prepared mix containing potting soil with peat-free compost, silt, perlite, and peat moss.
• To prepare an organically rich soil mix, use organic compost or manure, preferably granules with a balanced NPK ratio of 10-10-10.
• Water weekly to maintain good soil aeration and slightly moist condition.
• Avoid using sand or clay potting mix that will harden over time.
• Add lime to make the alkaline garden soil slightly acidic or neutral. It should be grown in rich organic soil with a pH between 6.0 to 6.5.

5. Low Temperature

Cucumbers are warmth-loving species that thrive in temperatures between 65 and 75°F (18 to 23°C) around the growing season.

Cucumber plants, especially those grown in colder climates, can succumb to temperatures low enough to cause a light frost overnight.

Yellowing of leaves, usually pale or whitish-yellow, can be an early indication of temperature stress.

When not treated in time, the plant will gradually fail to produce fruits or even die.

Solutions

• Grow Cucumbers indoors if you are in USDA zones lesser than 4. USDA zones 4 to 12 are considered ideal.
• Germinating Cucumber seeds require a temperature of 75°F, best attained in a warm location with ample sunlight or indoors under artificial grow light.
• Germinate seeds indoors before moving them outside in late spring.

6. Common Plant Pests

Yellowing Cucumber leaves may indicate pest infestation, like spider mites, whiteflies, potato leafhoppers, and aphids.

These sap-sucking insects feed on juicy Cucumber leaves, rendering yellowing hollow leaves.

Solutions

• Start with picking the visible insects from the leaves and dropping them in a soapy water solution.
• Spraying the entire plant row with a mixture of Isopropyl alcohol and water may kill all kinds of pests.
• Using a row cover may help prevent pests like Potato leafhoppers.
• Otherwise, spray or wash the plant with insecticidal soap effective against all major bugs, but follow the guide to avoid killing beneficial bugs.
• Make your garden clean and clear out all debris to avoid pest infestation.
• Use horticultural and Neem oil to control the insect population.
• Prune the infected plant to avoid further damage.

7. Horticultural Diseases

The garden-grown cucumber plants are prone to get infected with seasonal diseases that will infect most vegetative plants.

These diseases would mostly appear in Cucumber plants suffering from bacterial infection, infected soil, and wrong growing conditions.

Solutions

• Start with quarantining infected plants in case of indoor plants and destroy or drop diseased plants as soon as possible.
• Wash Cucumber plant leaves with a soapy water solution containing water and detergent.
• Use systemic or contact fungicides, such as Bonide 811 Copper 4E Fungicide, early to prevent the progression of the disease.
• Otherwise, use potent fungicides like Azoxystrobin, Flutolanil + Thiophanate-methyl, Tebuconazole, and PCNB to treat the infection effectively.
• Prune weeds and sick-looking Cucumber leaves as a preventive measure.

If you find white spots on Cucumber leaves, learn the causes and fixes!

Should I Cut Off Yellow Cucumber Leaves?

Yes, you can remove the yellow leaves on your cucumber plants.

Pruning yellowed and decayed leaves will help channel the energy toward healthy growth and fruits.

Leaves completely yellowed or tanned should be removed immediately, but those with minimal yellowing can be reverted to green with immediate treatment.

Here are a few tips for pruning your Cucumber plant.

• Prune the Cucumbers 3 to 5 weeks after they grow. 
• Remove decayed and yellow leaves regularly in spring and summer.
• Remove leggy growth with small leaves and suckers every week.
• Remove outside branches, leaves, and flowers, and develop fruits as needed.
• Use isopropyl alcohol to sanitize the tool before and after pruning to prevent the spreading of fungal growth.

FAQs Related to Yellow Cucumber Leaves 

Is it Ok to eat fruits from a yellow cucumber?

There is nothing to worry about consuming fruits until they are pulpy. Keep in mind that plant pathogens cannot harm your health. 

Why are my cucumber leaves turning yellow and brown?

The undersides of leaves deposit gray fuzz, which leads cucumber leaves to turn yellow and ultimately brown.

Freezing temperatures, overcrowding of plants, prolonged leaf wetness and excess humidity are some culprits to this issue.