Answer: For good performance, zinnias need full sunshine, warm temperatures, and regular watering. Soak the soil thoroughly when you water, and try to keep water off the foliage and flowers. Zinnias are subject to some diseases, including blossom blight and powdery mildew, as well as attack by a handful of insect pests. Look for signs of fungal infection (brown spots or a powdery white coating) or signs of nibbling by little caterpillars or beetles. If the flowers don't look diseased or eaten, the problem is probably cultural -- not enough sunshine and heat, or inconsistent soil moisture.
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