The most common reason tropical hibiscus buds drop is drying out too much.
Tropical hibiscus (Hibiscus rosa-sinensis) varieties may drop flower buds before they have a chance to open. This usually occurs when the plant is stressed. It can be tricky to diagnose the cause because different conditions can stress the plant. Some of the most common stressors are:
- Drying out. Tropical hibiscus flower buds will drop off the plant when the plant dries out too much. This often happens as or just after the plant begins to wilt. It's is the most common cause we see for hibiscus buds falling off.
- Inconsistent watering. When the plant goes through periods of staying moist, then drying out for a while, then staying moist, then drying out again, the hibiscus buds may drop off. To prevent this, try to keep your plants evenly watered.
- Sudden environmental changes. You might find your hibiscus drops buds when you first bring it home if your home environment is substantially different than that of the garden center (in terms of light, temperature, watering, etc.). Bud drop usually stops right after your plant gets settled. But other changes -- if there's an especially cold night after a warm day, for example -- can also put a little bit of stress on the plant.
- Heatwaves. Tropical hibiscus love warm, summer temperatures. But some varieties (especially older ones) can suffer when it's really hot (95F/35C or warmer).
- Being excessively rootbound. Especially cramped roots can cause hibiscus flowers to drop off. It's best to repot your plant as it outgrows the pot, particularly if you keep your hibiscus from year to year.
- Attack from pests. A variety of insect pests, including aphids and thrips, can weaken the plant. This causes buds to drop off before they open into flowers. Hibiscus planted in the ground in warm-winter areas like South Florida may suffer from nematodes. These small, nearly microscopic critters attack the plant roots, and can cause bud drop.