Why Are The Leaves On A Zucchini Plant Turning Yellow?

Zucchini plants are popular among home gardeners due to their fast growth and abundant yield. 

However, one of the most common problems that zucchini growers face is the leaves on a zucchini plant turning yellow. While some level of leaf yellowing on a zucchini plant is normal as it ages, excessive yellowing can be a sign of a problem that needs to be addressed. 

Just like other plants, zucchini contains chlorophyll that enables it to photosynthesize to make the leaves green. If a problem affects the plant, it becomes stressed, producing less chlorophyll; thus, the zucchini leaves turn yellow. 

The common causes of zucchini leaves turning yellow are; 

  • Nutrient deficiencies
  • Wrong soil pH
  • Watering problems
  • Improper lighting
  • Pests and diseases
  • Transplant shock
  • Damaged roots

In this article, we will explore the reasons why leaves on a zucchini plant turn yellow and what steps can be taken to prevent or treat this issue. By the end, you will better understand how to keep your zucchini plants healthy and thriving.

Causes of the leaves on a Zucchini plant turning yellow.

Zucchini are evergreen plants that don’t get yellow leaves unless there is a problem. So, if you notice the leaves are changing color, start acting on them early to ensure you save them before it affects the whole plant.

Let’s look at the problems causing zucchini leaves to turn yellow. 

Nutrient deficiencies

A plant requires sufficient nutrients to grow healthy. A lack of nutrients in the soil can cause the plant to struggle. Since zucchini is a heavy feeder, the soil should have enough nutrients, such as nitrogen, phosphorous, and potassium, as the primary nutrients. The other nutrients include iron, sulfur, and manganese. 

When the soil is low in iron and nitrogen, it will develop yellow leaves. The two nutrients are the main culprits to check when the plant has yellow leaves. In some instances, too much of these nutrients can also cause yellow leaves on zucchini plants. 

Besides that, too much phosphorus can prevent the plant from absorbing iron. So, check your fertilizer and ensure it doesn’t have too much fertilizer. Avoid cow manure; it has a lot of phosphorous. On the other hand, compost can correct nitrogen deficiency, and Chelated iron can help with iron deficiency.

The common nutrient deficiencies that can cause the yellowing of leaves in zucchini plants include: 

  • Nitrogen deficiency — nitrogen is important for the growth and development of leaves. When there is low nitrogen in the soil, the plant will have stunted growth, and the leaves will turn yellow.
  • Iron deficiency — The purpose of iron in a plant is to produce chlorophyll. Lack of iron causes the plant leaves to turn yellow (especially between the veins) because it doesn’t have the pigment to give them a green color. 
  • Manganese deficiency — A plant requires manganese to perform photosynthesis and to produce chlorophyll. If it lacks manganese, the leaves will turn yellow, and the plant will have stunted growth.
  • Zinc deficiency —- Zinc helps a plant to develop new leaves and promote plant growth. A lack of zinc can lead to the zucchini leaves turning yellow and producing small-sized leaves. 

When fertilizing the soil, ensure you purchase well-balanced fertilizer containing all the necessary nutrients. Test your soil regularly to determine if it lacks or has enough nutrients before adding fertilizer. Purchase a home test kit to test the soil at home. 

Wrong soil pH

Soil pH can cause the yellowing of leaves on zucchini plants because it affects the availability of nutrients needed to grow and function properly. The optimal pH range for zucchini plants is between 6.0 and 7.0. If the soil pH is too high or too low, certain nutrients may become unavailable to the plant, even if they are present in the soil.

For instance, if the soil pH is too low (acidic), the plant may not be able to absorb essential nutrients such as calcium, magnesium, and phosphorus. This can cause the leaves to turn yellow and stunt the plant’s growth.

On the other hand, if the soil pH is too high (alkaline), the plant may be unable to absorb nutrients such as iron, manganese, and zinc. This can also cause yellowing of leaves and stunted growth.

To prevent soil pH from causing yellowing of leaves in zucchini plants, it is important to test the soil regularly and adjust the pH level as needed. Adding amendments such as lime or sulfur can help raise or lower the soil pH, respectively. 

Additionally, adding organic matter, such as compost, can help correct the soil pH and be useful to the plant to help improve its overall health and fertility. It can help prevent nutrient deficiencies and yellowing of leaves.

Watering problems

Another problem that results in leaves in a zucchini plant turning yellow is water. Water can be excess or too little. Optimum amount of water is when the soil is moist and the plant is healthy. 

For instance, underwatering occurs when the plant receives little water. When there is no water in the soil, the plant cannot absorb nutrients from the soil or transport nutrients to the stem and leaves; thus, it struggles to get nutrients and feed the other parts. As a result, it becomes stressed, leaves turn yellow, wilt, and eventually die. 

On the other hand, overwatering gives the plant more water than it needs. You can notice overwatering if there is stagnant water on the soil or if the soil feels wet. The water makes the soil around the roots compact, and that can lead to root rot. The first sign of root rot is yellowing leaves in zucchini plants, usually the lower leaves. 

The leaves can also turn yellow if there is inconsistent watering. Inconsistent watering causes plant stress because the soil becomes too wet or dry. And as a result, it cannot absorb nutrients and water properly. 

To avoid yellow leaves on zucchini plants, consistently water the soil. Ensure the soil is well draining and has good water retention capacity. 

A zucchini plant can grow in most areas with one inch of water per week. But it depends on your location, weather, temperature, and time of year. You can use a moisture meter to check the moisture content in the soil or use the finger test before adding water to the soil. You can purchase a moisture meter here. 

Improper lighting

A zucchini plant grows well in an area with bright direct sunlight for 6 to 8 hours. Without proper lighting, the zucchini leaves will turn yellow. 

Move your plant to an area with enough sunlight. If it grows indoors, you can use a grow light to provide adequate lighting. You can purchase a grow light here. 

Pests and diseases

For any plant, pests, and diseases are a common problem. It’s better to prevent these two from attacking your plant rather than trying to treat them. 

For instance, the common diseases that can cause yellowing on zucchini leaves include; Fusarium wilt, cucumber mosaic virus, yellow virus, and Downey mildew. 

Fusarium Wilt is a fungal disease that is spread by cucumber beetle. It thrives on a plant with excess moisture. To prevent it from affecting your plant, avoid overwatering the plant. Also, crop rotation can help prevent the spread of the disease. 

Aphids spread cucumber mosaic virus and yellow virus. To keep away aphids, you can practice crop rotation.

Downey mildew thrives in damp, cold, and crowded rooms. So if you have an indoor plant, ensure the room is warm and spacious. 

Common pests that can attack a zucchini plant include aphids, spider mites, squash vine bores, and helpful pests such as ladybugs and parasitic wasps. 

These helpful insects can help kill aphids and other pests attacking your plant. You can also blast water on the plant to wash them off. Mix the water with neem oil to kill all the pests and get rid of their eggs. 

Transplant shock

Transplant shock occurs when the plants are stressed after a transplant. When they are in shock, the zucchini leaves turn yellow, and sometimes the plant dies. 

There are many causes of transplant shock, but the main cause is moving the plant to unfavorable conditions without hardening off (preparing the plant to adapt to changes). 

For instance, a sudden temperature change can cause the plant to go into shock. So, ensure that you prepare the plant to avoid transplant shock. 

Damaged roots

Roots are the main parts of a plant that support its growth. So when the roots are damaged by pests, diseases, or other factors, they stop providing the plant with nutrients and water to grow. 

Since the damaged roots can’t provide nutrients and water, yellowing leaves on a zucchini plant is the first sign.