Why are my cucumber leaves turning yellow? 3 solutions to the common problem

'Why are my cucumber leaves turning yellow?' – it's an enduring question amongst gardeners who grow this quirky fruit – but the answer is simple. 

Knowing how to grow cucumbers is the same as any other plant: meaning light and water levels are crucial to healthy growth. So, if you notice your cucumber leaves turning yellow, it is likely down to one of these factors. 

Whether you're learning how to grow cucumbers vertically – or you're growing from the ground or pot – your fruit is not immune from yellow leaves. Here's exactly what causes discoloring and how to avoid it in your produce. 

Why are my cucumber leaves turning yellow? 

According to Tom Hilton, director of outdoor and indoor garden specialists at National Greenhouse, yellowing occurs when the leaves lose chlorophyll – a pigment that gives plants their green color. Chlorophyll also aids photosynthesis (allowing the plant to convert light into energy). 

'The minute you see those cucumber leaves yellowing, it's time to take action,' Tom says. 'The main causes of this discoloration can be issues with the soil, overwatering, and of course, sunlight problems.' 

Alongside these key problems, Oliver Hill, Founder of Garden List, suggests that pets may be responsible for yellowing leaves. 'Aphids, whiteflies, and cucumber beetles are all common pests that can damage cucumber plants,' she adds. 'If you suspect that your cucumber plant is suffering from one of these problems, be sure to take action immediately to keep your plant healthy.'

How to stop cucumber leaves from turning yellow

Knowing when to plant cucumber seeds is one way to set your fruit up for success, but perfecting a care routine is equally impactful. Here's what the experts recommend.

1. Maximise sunlight 

Your cucumber plants should receive at least six hours of sunlight daily – to boost their health and avoid discoloring. If your cucumbers aren’t getting enough sunlight, they will likely droop, and yellowing will appear in the leaves. Therefore, Tom suggests moving your cucumbers from shady spots (where possible) to a sunnier area of your garden. 

2. Avoid overwatering

Emma Loker from DIY Garden explains that overwatering is one of the most common reasons your cucumber leaves turn yellow. Knowing when to water plants is key to their success, but what is the best time for the job? The expert recommends watering in the morning – avoiding the leaves as this 'encourages diseases.'

However, 'the best way to water cucumber plants is using a drip irrigation system or soaker hose,' Emma says. This allows you to keep track of the water levels, so your crop is never at risk of drowning. 

3. Monitor nutrients in the soil

Your cucumber plant's diet is another crucial issue in regard to yellowing. 'You should check the cucumber plant is getting the right soil nutrients,' Tom instructs. 'Potassium and nitrogen are two key ingredients they love, helping to encourage growth in foliage and keeping the leaves healthy and green.

To ensure your cucumber receives a good diet, you can invest in a cucumber fertilizer that fills the soil with everything they need to grow healthier. 

Should I cut yellow leaves off cucumber plant?

Yes, it is better to remove any leaves that have turned yellow as they may limit light from reaching the healthy part of your fruit. It will also encourage air circulation, which is beneficial to the plant overall. However, after removing the leaves, it is important to follow the prevention steps above to allow other leaves to grow healthier for a tasty crop.

What do overwatered cucumbers look like?

Overwatered cucumbers often show signs of yellowing leaves first. As Emma suggests, finding the correct water levels is imperative to your fruit's success, and if you're overwatering them, your leaves will suffer. To avoid this, you should water slowly in the morning or set up a drip irrigation system that monitors the water levels automatically.