Why Are My Cucumber Leaves Turning Yellow? How to Prevent and Correct These Top 5 Causes

Cucumbers have to be my favorite summertime crop. 

I mean, what’s more refreshing than chomping into a cool, crisp cucumber after toiling in the garden on a blistering summer afternoon?

Nothing tops that moment of plopping down in the shade and rehydrating by devouring a few green cukes fresh off the vine. 

I would be just as content making giant batches of dill pickles, except the fresh cukes never last long enough!

And as quickly as they disappear from my kitchen, they’re just as ephemeral in the garden.

It seems every year I plant cucumbers their window of production shrinks in duration. Sure they yield a ton during that time frame, but they always seem to fizzle out too quick. 

I dread the day when I begin to see yellow leaves creep up my cucumber vines. What a devastating sight.

So, once and for all, I’d like to get to the bottom of this problem that perenially plagues me. 

What causes my cucumber leaves to turn yellow? 

And more importantly, how can I treat this problem and prevent the leaves from yellowing in the first place?

Causes for Cucumber Leaves Turning Yellow

Any plant malady can leave you scratching your head. In your mind you did everything right, yet your cucumbers still seem unhappy. 

What gives?

We gardeners do our best to keep our plants happy and healthy, but we’re not perfect. The fact is, it’s easy to overlook problems our plants are facing if we don’t know exactly what we’re looking for. And the garden can be a busy, crowded space where many things easily go unnoticed.

In order to simplify the matter and get to a solution asap, I’ve listed the most common causes for cucumber leaves turning yellow, along with how to prevent and treat them.

Watering Issues

Cucumbers typically need 1-2 inches of water per week. During times of drought, extra water is required and it might be necessary to water every day. Installing a drip irrigation line helps to ensure that soil stays moist while saving you time from constantly watering. 

On the other hand, well-draining soil is crucial for healthy cucumbers. Sitting in damp soil for too long will quickly lead to problems.

Overwatering and underwatering are both causes of yellow leaves on your cucumber plant.

How to Prevent

You can prevent overwatering by measuring how much water your cucumber receives on a weekly basis. As stated above, 1-2 inches per week is a good general goal. A rain gauge in the garden is a handy tool that will let you know exactly how much water you’ve received in the form of precipitation. 

The more important factor to consider though is the moisture of the soil in real-time. Invest in a moisture meter so you can detect the exact level of moisture in your garden soil. 

Cucumbers do like their roots to be cool and on the moist side, so don’t ever let them dry out completely. Make sure the root level of your cukes retains a medium level of moisture and give water once the top inch of the soil has dried out. 

Withhold watering after periods of heavy rain. The plants will take up all the water they can and this can lead to swollen, bitter-tasting cucumbers. Wait until the soil dries out a bit before watering again.

To guard against underwatering two tools will be your best friend: Drip irrigation and mulch. 

A drip line can be turned on and off when needed, giving your cucumbers a steady, gentle watering. It also helps keep water off of the foliage, which can lead to the spread of fungal diseases. Some irrigation systems can even be programmed on a timer to regulate their output. This is especially helpful for busy or forgetful gardeners (I certainly fall under this category.)

Mulch not only suppresses weeds and prevents soil splash, but it keeps the roots of your cucumbers comfortable. Roots won’t get too warm and dry out as the mulch does wonders for retaining moisture. The need for constant watering and moisture moderation is alleviated through the simple act of applying a nice layer of mulch around your cukes. 

How to Treat

The best way to treat overwatered cucumbers is by being patient, letting the soil dry out a bit and praying it doesn’t rain. There’s not much else you can do other than let it dry out before watering again, then establishing an adequate watering routine. 

If the soil is extremely damp, you can try to use a small garden fork to break it up in the hopes that it dries out quicker. But this could lead to problems as cucumber plants tend to develop shallow roots. Working in the garden in wet conditions can contribute to the spread of disease. 

To treat underwatered cucumber plants, the solution is obvious: Give them water! 

Cucumbers are a plant that cannot tolerate being dried out, they will fail and die very quickly under these conditions. To address an underwatered plant, gradually give it a good amount of water. Too much all at once however could drown it or lead to rapidly growing fruits that are inedible. So take your time and water slowly to bring it back to good health.

Not Enough Sun

On the list of cucumber requisites, the sun comes second only to water, and it’s a close second. Like its squash and melon relatives, cucumbers love full sun. They’ll take as much as possible, provided they’re appropriately watered. A lack of vital energy from the sun could spell disaster for your cucumbers and turn their leaves yellow. 

How to Prevent

Choose a full sun site for growing your cucumbers. If it can’t be full sun, make sure they at least receive sunlight for the majority of the day. Otherwise, it won’t be worth planting them in that spot at all. 

The sunlight is a key element in photosynthesis and an abundance is needed for the plants to grow, thrive and produce healthy cucumbers. A lack of it will certainly lead to yellow leaves, as plants also need sunlight to produce green-pigmented chlorophyll. 

If possible, trellis the cucumber vines. This will allow the sun to access more parts of the plant. It’s easy to lose track of cukes that are hidden under the clutter of tangled vines and bushy leaves. This type of environment can also invite disease.

How to Treat

Trellising can also be a treatment if your cucumber plant isn’t receiving enough light. If that’s not possible at least let the vines sprawl freely and make sure all parts of the plant get exposure to the sun. This may mean pruning off a vine or two that’s underperforming, sickly or dead to open up the plant. Leaves can be pruned off to encourage the sun’s penetration. Prune lightly and sparingly and only if you deem it necessary.

Pests

Because they’re so lush, green and shade-producing, many pesky bugs will make food and a safe haven out of your cucumber plants. This can be especially annoying if an invasion is caught too late. Luckily there are methods for prevention and treatment. 

How to Prevent

If you don’t want pests to be a problem on your cukes, you have to be proactive. 

Another consequence of not enough sun is that it turns into an open invitation for pests. Most soft-bodied pests like aphids, whiteflies and spider mites enjoy warm temperatures but can’t withstand the harsh direct rays of the sun. Just by keeping the plant open and well spread out, you can avert most pest issues.

Keeping your plants healthy and well-watered and nourished is probably the best way to prevent pests. Detrimental bugs tend to target and pick on weak or sickly plants. By keeping yours robust, you can greatly reduce the risk of attracting pests.
Another wonderful way to prevent pests from establishing on your cucumber plants is by cultivating companion plants like dill and onions close by your cucumbers. Dill welcomes in beneficial insects like ladybugs, lacewings, predatory wasps and praying mantids that prey on pests. Onions deter many types of common garden pests.

How to Treat

If the pests have infiltrated and it seems too late to prevent their presence then you must act by taking more drastic measures. But before you consider any chemical treatment, which I advise against totally, consider one of these natural remedies. There’s always an organic solution in my opinion.

Insecticidal soap or neem oil can be diluted in water and put in a spray bottle. Once the sun has set for the day, give the whole plant, especially the problem area a thorough misting with the insecticidal spray. Beware that while it won’t be toxic to your plant or those consuming the produce, these sprays kill indiscriminately and may harm some beneficial bugs in your garden.

Diatomaceous earth is another excellent all-natural pesticide. It’s a fine dust that’s made up of crushed shells that are fine and razor sharp. The dust smothers and slices open soft-bodied pests. Put it into a duster tool and spread it around the base of the plant, onto the foliage and concentrate on any problem areas. It’s harmless for humans, just keep away children and pets as it can agitate respiration. 

Always wash produce well after it’s been treated by an insecticide, natural or not. 

If possible and practical (it may not be) some pests can be removed or knocked off the plant by hand. Aphids are actually quite weak and can be smushed or knocked off by a strong blast of water. Just be careful as they usually attack new growth and fragile areas of a plant.

Diseases

Cucumber plants are unfortunately susceptible to many pervasive diseases. I believe this is what ultimately does in my plants every year. Either disease or the next problem, nutrient deficiencies. 

Contraction of disease may be the most common reason for cucumber leaves turning yellow. Chances are you’ll run into one of these common diseases at some point:

Downy Mildew

This bothersome disease thrives in wet and humid conditions. It will cause yellow spots on leaves, turning the entire leaf brown and eventually killing them. 

To prevent downy mildew, you can plant resistant varieties, keep foliage dry and give plenty of space between cucumber plants encouraging efficient air circulation.

To treat downy mildew remove infected parts of the plant and apply a fungicide. Hydrogen peroxide and baking soda are clean, natural substances that do a good job of keeping fungal diseases in check.

Fusarium Wilt

Another killer disease, fusarium wilt is caused by a fungus that can live for long periods of time in the soil or among plant debris and brush. Once infected, leaves will turn yellow, growth is stunted and the plant itself will wilt and damp off. 

When the plant starts to wilt, it’s only a matter of a few days before it dies. There is no way to treat fusarium wilt once it sets in. That’s why it’s extra important to prevent it from spreading.

To prevent fusarium wilt make sure to keep the growing space around your cucumber plants clean and free of any dead, dying or decomposing plant debris. Always clean garden beds of debris in the fall and spring. Definitely do not let any infected plant debris remain in the bed over the winter. 

Preemptive treatments with hydrogen peroxide solutions can help prevent it from surviving in the soil and spreading to the plant. Make sure to keep the foliage of the plants dry and that you don’t overwater. Allow proper spacing between cucumber plants to ensure proper airflow. 

Cucumber Mosaic Virus

This disease is pest born, being spread by aphids. It manifests in little yellow spots or patterns on the leaves of cucumber plants. Cucumber mosaic virus is another serious disease that can’t be treated once your plant is infected. 

An infected plant and any surrounding weeds should be removed entirely from the garden and destroyed. 

In order to prevent your plants from contracting this deadly disease, follow the instructions for preventing pests and the standard precautionary steps for disease prevention. 

Soil Deficiencies

Every plant needs certain levels of nutrients from the soil for nourishment and cucumbers are no exception. In fact, cucumbers are quite heavy feeders as they require plenty of nutrition to grow vegetatively, flower and produce healthy fruit. 

If the soil is devoid of any nutrients they need, you’ll notice leaves begin to turn yellow and production will suffer. 

How to Prevent

The best way to address nutrient deficiencies is by adding well-broken-down compost to the garden bed every spring and supplementing throughout the season. Compost has the ability to increase nutrient uptake in your plants. Many times a deficiency isn’t necessarily the case, but the lack of organic matter inhibits your plant from absorbing the critical minerals. 

Another wise action to take is to get your soil tested. The fall before planting is the best time, as this will give you an opportunity to amend the soil. 

Growing a cover crops or green manure is a tenet of polyculture farming that helps to regeneratively feed the soil in a natural way. These plants can replenish the soil with the nutrients your garden crops will need. 

How to Treat

Applying natural fertilizers throughout the season is a good way to renew the nutrient levels that can start to wane as your cucumber plant consumes them. 

Use fish emulsion, blood meal, feather meal or alfalfa meal to give your cukes a huge boost of nitrogen. These fertilizers will guide your plants to a strong start by contributing to vigorous vegetative growth.

If they’re lacking phosphorus, opt for bone meal or crustacean shell meal. These fertilizers can be worked into the soil early in the season, at the time of planting or as a top dressing throughout the season. Phosphorus will be especially critical during the flowering period. 

Other natural fertilizers like liquid seaweed, Epsom salt and molasses will add potassium and plenty of other micronutrients like magnesium, calcium, iron, manganese and zinc. 

A Cool, Crisp Conclusion

So as we’ve learned there’s a whole heap of reasons your cucumber leaves are turning yellow. 

It’s up to you to note the growing conditions and environment and observe the plants closely in order to identify the most likely cause. 

Then, action is required. 

Take the recommended steps suggested in this article to attack the root cause of the issue, or to treat it the best you can.

Armed with this knowledge, I’ll be extra vigilant and take all the necessary precautions. 

Because this year, you better believe I’m going to make that batch of dill pickles!