A: When hibiscus plants drop their buds, it’s usually a sign of stress. Figuring out the cause can be tricky, but there are a few likely reasons:
- Though hibiscus plants love heat and humidity, temperatures over 95°F can stress them. Thinking they may be about to die, they drop their buds as a defense mechanism. Help your hibiscus keep its cool by providing consistently moist soil and some protection from afternoon heat.
- Hibiscus hate being moved and will often drop their buds in protest. Once the plant has settled in again, the problem should disappear.
- Over-fertilization, nutritional deficiencies and environmental factors, such as poor drainage, can cause bud drop.
- Several insects can cause bud drop:
Thrips - Hold an almost-open bud over a piece of plain white paper and flick it with your finger. If you see a sprinkling of little black flecks, they’re probably thrips. Liquid pyrethrum is an effective control.
Mealybugs - Check the stems for their fuzzy white egg sacks; use alcohol-soaked cotton swabs to remove them.
Hibiscus gall midge - This pest causes buds to turn yellow and drop. It lays its eggs inside the flower buds; as the larvae develop, their feeding causes the buds to drop. A hibiscus-safe liquid systemic insecticide is the best way to control this troublesome pest. — Kathleen LaLiberte, garden writer and industry consultant