Why do cucumber leaves turn yellow in a greenhouse and what can I do about it?

People who regularly grow cucumbers often encounter yellowing on the surface of their leaves or fruits. To get rid of this problem, it's important to understand why cucumber leaves turn yellow in a greenhouse and what to do to resolve the issue.

Causes of yellowing cucumber leaves in a greenhouse

There are several reasons why cucumber bush leaves begin to turn yellow.

Excess or lack of fertilizers

It's no secret that when growing cucumbers, fertilizers are added to the soil to enrich it with nutrients. Due to excessive fertilizer use, the lower leaves of cucumber seedlings turn completely yellow. Gradually, the yellowing spreads to the upper leaves. To eliminate the yellowing, you'll need to stop adding fertilizer until the nutrient balance stabilizes.

After this, resume adding fertilizers:

• in spring - once a month;
• in summer - twice a month.

Sometimes leaf discoloration indicates chlorosis, which occurs when the soil lacks iron. This condition can be eliminated by adding diluted lemon juice to the soil.

Hypothermia of bushes

Cucumbers are considered heat-loving vegetables and do not thrive in cold conditions, so they are recommended to be grown at temperatures above 5-10 degrees Celsius. However, some gardeners want an early harvest and plant them in early spring. Young seedlings quickly freeze, causing yellow spots on the leaves. Over time, the yellowing completely covers the leaf blade.

If cucumber seedlings are not replanted and continue to grow in the cold, they will die. Therefore, to preserve the planted vegetables, they are transplanted into a heated greenhouse.

Overheating in the sun

People growing vegetables in greenhouses often face the problem of overheating. Summer and spring are the most common periods for cucumbers to overheat in greenhouses. Constant exposure to sunlight and elevated temperatures negatively impacts the health of the plants.

Due to overheating, the leaves located at the top of the bushes change color and turn yellow.

To solve the problem, you will have to shade the greenhouse to protect the seedlings from sunlight..

Problems with the root system

Most often, problems with cucumber seedlings indicate a problem with the root system. If the roots don't have enough space, they don't grow well, causing each leaf to turn yellow. This happens when cucumbers are grown in pots, where there's not enough room for the root system to expand.

However, yellowing can also occur because the roots have too much room to develop. This causes them to constantly grow and consume too many nutrients. If this problem is not addressed promptly, all yellowed bushes will die.

Irregular watering

It's common knowledge that cucumbers, like many other vegetables, need regular watering. If this isn't done, the ovaries and leaves will grow poorly and gradually turn yellow. Experts recommend watering the plants at least three times a week. This will help maintain optimal humidity levels. Use water warmed to room temperature. Avoid using water that's too cold, as it will cause root rot.

Leaf aging

In the second half of summer, cucumber leaves begin to age and develop yellow spots. This yellowing occurs due to slower photosynthesis and reduced nutrient supply. It's impossible to prevent leaf ageing, as it's a natural process.

All the aged leaves gradually dry out and fall to the ground. Bushes that are losing their leaves can be dug up and removed from the greenhouse or garden.

Infections

Another reason why plants begin to dry out is infectious diseases. There are several infectious diseases that most often appear when growing cucumbers.

Fusarium

The disease appears in the summer, when temperatures reach 35 degrees Celsius (95 degrees Fahrenheit). Spores enter the plant through the root system and gradually infect the entire bush. It's difficult to immediately identify the symptoms of fusarium, as they develop gradually. Initially, each lower leaf becomes covered with yellow spots. Gradually, the yellowing spreads to the entire leaf blade, causing the leaves to dry out.

The main signs of pathology include:

• rot at the root and root collar;
• staining of the stem brown;
• yellowing of leaves;
• dying off of ovaries;
• lack of flowering.

Powdery mildew

Another reason for leaf tips turning yellow is powdery mildew. The disease occurs in conditions of high humidity and high temperatures. Spores also thrive in low light.

Powdery mildew initially causes the leaves to become covered with a white coating. If left untreated, each leaf will turn yellow and dry out. To combat the condition, use a soap solution, whey, and nettle infusion.

Downy mildew

This is a dangerous disease that affects not only the foliage but also the fruit. Most often, this infectious pathology appears if undisinfected seeds were planted. It also occurs if chemical fertilizers were frequently used. Downy mildew slows photosynthesis, leading to yellowing of vegetable leaves.

The disease is characterized by its rapid development, causing infected bushes to die within a week.

When the disease appears, the leaf edges turn yellow and develop a grayish tint. The shoots of the bushes crack and become deformed, and the fruits wither.

Root rot

If cucumber seedlings are insufficiently fed and watered, they will become infected with root rot. This condition often occurs in weakened plants under conditions of high humidity and low temperatures. The main sign of root rot is wilting leaves. The following symptoms also appear as root rot progresses:

• the leaves begin to curl;
• root rot;
• cracking of the main shoot;
• yellowing of the lower part of the stem.

Insect pests

There are several dangerous pests that cause cucumber seedlings to turn yellow.

Spider mite

Spider mites are small insects that often attack vegetables in polycarbonate greenhouses. These pests feed on plant sap, causing foliage to wilt. Spider mites also cause some vegetable crops to become infected with gray mold. The main signs of a spider mite infestation include:

• slowing down of seedling growth;
• formation of a web between the stems;
• white spotting on the surface of the leaf blade.

Melon aphid

Melon aphids most often appear when cucumbers are planted outdoors. However, they sometimes also attack plants grown in greenhouses. Like spider mites, these insects feed on the sap of young plants. This leads to the weakening of seedlings and yellowing of the foliage.

If melon aphid control is not carried out in a timely manner, cucumber seedlings will dry out and die.

Methods for combating yellowing

Many inexperienced vegetable growers don't know what to do if the leaves of their greenhouse cucumbers turn yellow. There are several common methods for eliminating yellowing of cucumber tops:

• Onion infusion. This is the most popular folk remedy for yellowing. To prepare the infusion, pour boiling water over a half-liter jar of onion peels. Then let it steep for twenty hours. The cooled solution is sprayed on the leaves and poured onto the root.
• Milk-soap solution. This is an effective remedy for pests and many diseases. To prepare the solution, add 30-40 drops of iodine, 30 grams of bar soap, and 40 ml of milk to a liter of water. Mix all ingredients with 8-10 liters of water, after which the solution can be applied to the tops.
• Nettle fertilizer mixture. To make the mixture, soak 200 grams of fresh nettles in water and mix with mullein. This fertilizer can only be used after the seedlings have developed their fifth leaf.

Preventive measures

To avoid wasting time treating yellowing in the future, it's important to familiarize yourself with the specifics of yellowing prevention. Regularly treating the tops with fungicides will prevent pests. Also, feed cucumber seedlings with organic and mineral fertilizers, which will enrich the soil with nutrients and strengthen the plant.

Conclusion

Greenhouse cucumber growers sometimes encounter yellowing leaves. To quickly eliminate this, it's important to understand the causes and effective treatments.