Any Amazon links below are affiliate links, which means I earn a commission at no cost to you if you click and finalize an order. As an Amazon Associate, I earn from qualifying purchases.
Yellow Leaves on Cucumber Plants in Containers
If you’ve started growing cucumbers, you may have noticed that they sometimes get yellow leaves, particularly when they’re in containers. The good news is that, in most cases, it’s fixable! Here’s a full list of reasons why you may have yellow leaves on cucumber plants in containers, along with what you’ll need to do to get them back to their normal, happy, green selves.
6 Reasons Why Your Cucumbers Have Yellow Leaves
The following are all common reasons why your cucumber plants may have yellow leaves. Most apply to in-ground cucumbers as well, not just those grown in a container!
For many plants, including cucumbers, overwatering can lead to yellow leaves. Cucumbers need an average of 1-2 inches of water per week, so if you’ve been watering them frequently (or if it’s overly rainy) they can receive too much. It can be especially hard to tell when you keep your cucumber indoors, since the water may not dry as quickly as it does outside.
The Overwatering Fix
Check your soil! If the soil is still damp when you press your finger 2-3 inches into the dirt, there’s no need to water again. Wait until it’s dry. And if your soil is sopping wet, cut back on how much water you give your cucumber at a time.
Also check whether or not your container has a drainage hole. While you might assume your pot has one, some have to be added manually. Without at least one drainage hole, your cucumber could be sitting in water and rotting, even if you otherwise give it a normal amount. Drill holes into your container, or transplant the cucumber into a pot that has one or more holes already in it.
Conversely, you may be giving your cucumbers too little water. A dehydrated cucumber can also have yellow leaves, along with wilting.
The Underwatering Fix
If your cucumbers are underwatered, the solution is, once again, to check your soil regularly! Press your finger into the soil 2-3 inches down. If it feels dry, it’s time to water again. Check daily for a week or two until you get a good idea of how much water your cucumber needs. Once that’s established, you can create a watering schedule for it accordingly.
A variety of diseases and fungi can give your cucumbers yellow leaves. Cucumber mosaic virus, fusarium and verticillium wilts, and downy and powdery mildews are all common problems for cucumbers.
Cucumber mosaic virus causes a cucumber’s leaves to get yellow spots on them, as well as wilting and weakening them.
Cucumbers are susceptible to both fusarium wilt and verticillium wilt. Both can cause the plant’s leaves to yellow, wither, and die. It helps to know how to identify the two.
Both downy mildew and powdery mildew can turn a cucumber’s leaves yellow. The main difference between them is that powdery mildew looks like a white, moldy powder on all parts of the leaf and stem, while downy mildew gives the leaves yellow and brown spots, with dark mildew appearing on the underside of the leaf. Here’s a full list of differences, along with more information about each type.
Unfortunately, most cucumber diseases can’t be cured. The best option for mosaic virus and both types of wilt is to pull up and dispose of the affected plants (preferably by burning), then bleach your tools and container and use completely fresh potting soil so that your new batch won’t be infected. Keep in mind that some diseases can be spread by bugs, so consider changing the area you keep your cucumber container in, or even growing the new plant inside.
The exception to the rule is mildews, which generally won’t require pulling up the plant except in extreme cases. Downy mildew is more harmful than the powdery variety, but can still be cured if the affected leaves and stems are pruned and the plant is opened up for more airflow. Both mildews benefit from increased airflow and watering the soil directly (without getting water on the leaves and stems). Aside from pruning, another way to give cucumbers added airflow is to invest in a trellis for them to climb on.
Aphids, cucumber beetles, potato leafhoppers, spider mites, and whiteflies all feed on cucumber plants, which can ultimately lead to yellow leaves. Worse, even if the pests haven’t turned the leaves due to their feeding, they can still spread many of the previously mentioned diseases. Inspect your cucumber plant (especially underneath the leaves and stem) for any of the following:
Aphids – Green or black bugs about the size of uncooked rice (or smaller). You may see only a handful, or there may be hundreds infesting your cucumbers and the surrounding plants.
Cucumber beetles – Small yellow bugs with black stripes or spots. They will nibble holes in your cucumber’s leaves, along with the leaves of any other nearby squashes.
Potato Leafhoppers – Potato leafhoppers are green and winged, unlike the other notorious potato pest, Colorado potato beetles.
Spider Mites – Spider mites are very small red insects that can leave spider-like webs on the underside of leaves.
Whiteflies – Whiteflies are very small white, winged insects. They’ll fly away if you shake the leaf they’re sitting on.
Depending on what pests you have, you can either directly treat the problem using a pesticide solution, or, for less overrun crops, pick the bugs off individually.
Most bad bugs can be waylaid with insecticidal soap. For larger insects, like cucumber beetles, you can gather the bugs as you spot them in a bag or jar, then destroy it.
#5: Poor Soil
Improper nutrition can cause your cucumbers to yellow.
Poor Soil Fix
If your cucumber is lacking in nutrients, you can add cucumber fertilizer. You may also consider transplanting the cucumber into another pot with better potting soil. Most vegetable mix soils have just the right nutrient balance for prosperous cukes.
#6: Lack of Sunlight
Cucumbers generally need 6-8 hours of sunlight per day. If they don’t get enough, their leaves may turn yellow.
The solution for your cucumber not getting enough sunlight… is to place the container in a space where it can get more sunlight! Leave it an area with 6-8 hours of sun, and you should start to see an improvement. If you use grow lights, it may need up to 16 hours of light for an equivalent day, since they aren’t as powerful.
Happy Cucumber Growing!
With these tips, you should be able to identify why there are yellow leaves on cucumber plants in containers (or why there are yellow leaves on any cucumber plant at all!). Enjoy your cucumbers!
Did you know deer avoid cucumbers, along with many other garden favorites? Check out the full list of deer resistant vegetables and herbs.