July 10, 2025, 8:47 am | Read time: 2 minutes
Healthy zucchini plants are characterized by robust growth and lush green leaves. It becomes all the more concerning when yellow discolorations suddenly appear. Many hobby gardeners then wonder: Is this still normal, or is it a sign of a deeper issue? Those who identify and correctly interpret yellow leaves early can often save their plants in time. myHOMEBOOK gardening expert Franka Kruse-Gering outlines four possible causes.
Zucchini are among the most uncomplicated and rewarding garden vegetables. They grow quickly, produce abundantly, and are remarkably robust with proper care. This makes it all the more concerning when their usually vibrant leaves suddenly turn yellow. Is this just a temporary issue, or is there more to it? Yellow leaves are often an early sign that the plant is out of balance. Those who take this change seriously and look closely can usually identify the causes and restore the zucchini to balance.
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Why Zucchini Have Yellow Leaves
In addition to pests, a variety of other factors can cause zucchini plants to become unbalanced and their leaves to turn yellow. These include unfavorable environmental conditions, care mistakes, or diseases.
Incorrect Watering Leads to Yellow Leaves on Zucchini
Zucchini need a lot of water regularly because they grow quickly and have large leaves. The large leaves cause the moisture to evaporate very quickly. It is important to ensure that the soil is neither too dry nor too wet to prevent root rot. Ideally, water in the evening so the plant can absorb the water overnight. On particularly hot days, it is advisable to water both in the morning and evening.
Nutrient Deficiency
The plants are heavy feeders, meaning they require a lot of nutrients to grow well. Regular fertilization is important. You should also pay attention to the neighboring plants. If you plant heavy feeders next to zucchini or place individual zucchini plants too close together, they may compete for nutrients.
Shock from Temperature Changes
Even though zucchini appear robust, they can be quite sensitive. They do not tolerate sudden temperature changes well, which can result in yellow leaves, though usually, the older leaves are more affected. If a weather change is expected, protect your plants, for example, with a fleece overnight. You can also cover them with a box.
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Infestation with Fungal Diseases
Whether it’s powdery mildew or downy mildew, both fungal diseases prefer to settle on zucchini. To prevent this, always ensure adequate ventilation for the plant. Downy mildew occurs in warm, humid weather, while powdery mildew occurs in dry, warm weather, which is why it is also called the fair-weather fungus.