Why Are Your Cucumber Plant Leaves Turning Yellow?

When it comes to growing cucumbers, vibrant green leaves are a sign of a healthy plant. So, why are your cucumber leaves turning yellow? In this article, we’ll explore five common reasons behind this issue and provide solutions to help you restore your plants to their full health.

Nitrogen Deficiency

All plants rely on nitrogen to produce chlorophyll, the pigment responsible for their rich green hue. Without an adequate supply of nitrogen in the soil, cucumber leaves will start to pale and turn yellow. Nitrogen deficiency is a prevalent issue since plants require a significant amount of this essential nutrient.

To address this problem, you can feed your plants with water-soluble fertilizer or amend the soil with compost during the spring and fall seasons. Another nutrient deficiency that can cause yellowing leaves is a lack of magnesium. The symptoms are similar: yellowing leaves with green veins. Applying an all-purpose fertilizer that contains all necessary nutrients is the best solution for both nitrogen and magnesium deficiencies.

Downy Mildew (Fungal Disease)

In regions like New England, cucumber plants often fall prey to downy mildew, a fungal pathogen also known as water mold. This troublesome fungus thrives in cool, damp, and humid conditions, quickly spreading throughout the plant’s foliage. Infected leaves display yellow spots with distinctive hard edges, and underneath, you may find dark purple mildew, which indicates the presence of spores.

To combat downy mildew, it’s essential to provide sufficient airflow by leaving more space between plants. Additionally, avoid watering over the tops of leaves and focus on watering at the base of the plants. Applying a fungicide can help control the spread of the fungus, but it’s crucial to water your plants properly to prevent further contamination.

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Cucumber Mosaic Virus (CMV)

Cucumber mosaic virus is a prevalent plant virus in North America, affecting a wide range of plant species, including cucumbers. This virus causes mottled discoloration on plant foliage, resulting in yellow and light green spots that often resemble a mosaic pattern. The virus is primarily spread by aphids, which pick up the virus particles from nearby weeds and transmit them to cucumber plants.

Unfortunately, there is no cure for CMV once plants are infected. The best course of action is to remove the infected plant entirely to prevent further spread. To minimize the chance of infection, monitor and control aphid populations using insecticidal soap. Planting CMV-resistant cucumber varieties can also offer protection against the virus.


Over-watering can hinder root development in cucumber plants. If your soil has poor drainage, it’s crucial to address this issue. Adding compost to your soil is an effective way to improve aeration, drainage, and moisture and nutrient retention. Make sure your containers have adequate drainage holes, and if one becomes clogged, cover it with a small rock before adding soil.

To tackle over-watering, check the soil’s dryness before watering and work on improving soil drainage. By amending the soil with compost every spring, you can provide your cucumber plants with the optimal growing environment. Conversely, under-watering can also cause yellow leaves, so be sure to water your plants when they show signs of wilting.

Pest Damage

Pests can cause significant damage to cucumber plants, including yellowing leaves. Common cucumber pests include striped cucumber beetles, cabbage loopers, cutworms, slugs, snails, whiteflies, and thrips. These pests may leave holes in the leaves and fruits, leading to areas that turn yellow or brown.

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Regularly check your plants for signs of pests, particularly underneath leaves, on new foliage growth, and in flowers. Using sticky traps and companion flowers to attract beneficial insects can help control pest populations. Hand-picking slugs, snails, and caterpillars during nighttime hours can also help minimize their impact. If necessary, treat your plants with insecticidal soap, making sure to avoid spraying during daylight hours.


While discovering yellow cucumber leaves can be disheartening, understanding the underlying causes can help you address the issue and ensure the continued health of your plants. Remember to remove diseased foliage promptly and give proper care to your cucumbers to prevent further spread. By employing the right solutions for nutrient deficiencies, diseases, over-watering, and pests, you can enjoy a bountiful harvest of healthy and vibrant green cucumbers.

For more gardening tips and advice, visit Ames Farm Center.