Cucumbers can be such a fun plant to grow, but they don’t come without their issues.
Yellowing cucumber leaves can be an early sign of big problems. While this issue might not seem like a big deal, it could actually be a sign that your plant is starting to experience some sort of stress. Here are five potential reasons why your cucumber leaves might be turning yellow.
5 Main Reasons Cucumber Leaves Turn Yellow
Cucumber leaves can turn yellow for several different reasons including diseases, pests damage, root rot, overwatering, and nutrient deficiencies. It’s important to identify the cause in order to take appropriate steps for treatment and prevention, so we can fix the issue.
When a cucumber plant begins to turn yellow, the cucumbers themselves can quickly follow suit, and then the cucumber harvest time will be significantly delayed.
If your cucumbers have white spots on their leaves then they may have been infected with powdery mildew which will need to be treated with fungicide or organic pest control.
1. Nutrient Deficiency
Cucumber plants are heavy feeders, needing a lot of nutrients and water.
If your cucumber plants have a yellow edge on the leaves it could mean that they are not getting enough of certain nutrients, namely nitrogen, iron, or calcium.
How to Fix It
You can fix a nutrient issue by fertilizing cucumber plants regularly. You’ll want to make sure you aren’t over-fertilizing, as this could cause further problems for the plant.
This fertilizer has a great 8-4-8 NPK ratio with enough Nitrogen to help with growth and leaf color, but also gives the plant the Phosphorus and Potassium it needs to stay strong.
How to Prevent It
It’s easy to prevent this issue from happening by making sure you are regularly fertilizing your cucumber plant. The fertilizer you use will have instructions for how to use it, so make sure you follow that to avoid a future nitrogen deficiency.
However, too much of a good thing is also not ideal, as you can cause “nutrient burn” by over-fertilizing your cucumber plants.
Adding too much fertilizer will cause the plant to have trouble taking in water, and since cucumbers are 95% water, this is a problem.
If your plant growth slows to a crawl, or you’re getting a ton of leaves but not flowers and cucumber fruit production, you may be over-fertilizing your plant.
How to Fix it
Stop fertilizing your plants for the time being.
Remove cucumber leaves that have yellowed to allow the plant’s energy to go into healthy, green leaves.
Wait a week or two to see if the problem resolves itself. If it does, check the directions of your fertilizer to make sure you are giving plants the right amounts of the product.
Give the plant about half of the dosage you were previously offering up. Wait and see if the leaves stay green.
How to Prevent it
Get a soil test done to see if your soil has too much of any one nutrient. This will help you better analyze which fertilizer to use in the future.
Follow the fertilizer instructions carefully to ensure you are not giving too much to the plant.
3. Pest Damage
Insects and diseases can be problematic for any plant to grow well, especially cucumbers.
A few common pests of the cucumber could be the cause of yellow leaves.
The potato leafhopper can cause cucumber leaves to first turn yellow, then turn brown and wilt.
They feed on the sap within the leaves, causing that part of the leaf to dry out and change color. If left alone, they can destroy the entire plant.
Spider mites can be really challenging to spot initially. Their webs are translucent, so they can easily pass a quick glance. Eventually, they will start to take over a full leaf and you will definitely start noticing them when the leaf begins to yellow and wilt away.
If cucumber leaves have small holes on them it can be an indication that the striped cucumber beetle has arrived. Cucumber beetle larvae feed off of cucumber plants leaving large yellow cucumber spots on cucumbers and cucumber leaves.
If cucumber beetles are allowed to cause enough damage, you will start to see delayed harvest time and yellow cucumbers.
Aphids are a nightmare in the garden. They can affect almost any plant, are hard to find, and can be tricky to get rid of. Aphids can also spread plant disease and other issues from cucumber plant to cucumber plant.
How to Fix it
If there is an infestation of pests on your cucumber plants, there are a few options you can take to get rid of them.
You can spray insecticidal soap, but unless you’re careful these can also kill beneficial insects.
- Diatomaceous Earth
- Neem oil
How to Prevent it
It can be hard to prevent pests so they don’t infect cucumber plants. But spraying neem oil regularly is my go-to method. You can also use row covers and follow cucumber companion planting guides to help repel certain garden pests.
4. Diseases That Affect Cucumber Plants
There are a number of plant diseases that affect cucumbers, so let’s walk through them and help identify infected plants and what your leaf discoloration means.
Cucumber Mosaic Virus
Cucumber leaves turning yellow can also indicate plant damage from mosaic virus.
This virus is generally spread by aphids who suck the sap out of one leaf, and then move on to infect other cucumber leaves.
Cucumbers with cucumber mosaic virus will have an overall yellow appearance aside from the green veins or spots between leaf veins in cucumbers. These cucumbers also often develop brown spots on the leaves as the damage progresses.
How to Fix it
To get rid of this problem, you’ll need to remove cucumber plants from cucumber beds and destroy them so the cucumber viruses won’t spread to nearby cucumbers. Do NOT add these plants to your compost pile as it could cause issues with next year’s harvest.
Even letting the plant die can cause issues for next year’s crop, as this disease can overwinter and come back with a vengeance.
If allowed to stay in the garden, aphids and other pests can transfer these to more cucumber or other cucurbit plants.
In my opinion, the effects of downy mildew look more like they should be called mosaic virus, but here we are. 🙂
Downy mildew starts off as white spots, but quickly starts sapping the energy out of the leaf cells and they turn pale green, then yellow, then brown.
If portions of the top of the leaves are turning yellow or showing yellow spots, this could be downy mildew.
Cucumbers require a large amount of water, but when they get too much water, this can introduce a host of problems.
Whether it’s from too much rain, or human error, overwatering can lead to yellowing leaves. When cucumbers are overwatered, the plant leaves will usually look something like this:
But wait, this is exactly what the plant looks like if it’s not getting enough water too. Well, that’s where it can get tricky. You’ll want to test the soil around the plant to see if it’s dry or not. If the soil is dry, water your plants because it’s very thirsty!
If the soil is wet, walk away slowly and don’t water it for a few days.
When the roots of a cucumber plant sit in water, they aren’t able to get enough oxygen and nutrients, and the leaves will start to wilt and turn yellow.
How to Fix It
If you suspect that your cucumbers are being over-watered, try giving them less water and see if it makes a difference. Allow the plants to dry out for a day or two before considering watering them again.
If your plants are outside and being overwatered, see if there is a way to help improve drainage around the plant
How to Prevent It
Check the soil around your plants before watering. If there is water found a few inches down into the soil, then hold off on watering. If that soil is dry, go ahead and water the cucumber plant.
Cucumbers are delicious vegetables that contain lots of vitamin C and potassium. They can provide a lot of yield per season, but don’t come without their problems.
By knowing cucumber plant problems, you can take action in advance and solve your issues.
Should I Cut Yellow Leaves off the Cucumber Plant?
I would recommend cutting the leaves off your cucumber plant if they are discolored and have severe damage. This will help the plant focus on growing healthy leaves, and reduce the plant stress moving forward.