April 21, 2022: Answer 3
Dear Neil: I have a very healthy rose-of-Sharon. It has lots of buds, but it rarely blooms. It is about 4 feet tall, and it’s covered in buds. But in its five years, it has never flowered very well at all. Suggestions? R.O., Richardson.
All members of the big hibiscus family are notorious for aborting their flower buds when times get tough. Roses-of-Sharon (althaeas) in particular seem to set most of their flower buds in late spring and early summer, while temperatures are still moderate and moisture is often bountiful. Then, as it turns really hot and dry, they start jettisoning their buds, almost as if out of concern that they have over-anticipated good conditions. The best thing you can do to help them hold onto many of the buds will be to keep the soil uniformly moist. Don’t let the plants wilt. Apply 1 or 2 inches of compost or mulch to slow the soil’s drying. Do check, too, for evidence of thrips in the buds. They’re very tiny sliver-shaped insects that will be down in the tight buds. They are also responsible for bud drop and poor opening. Systemic insecticides will control them within a couple of weeks, so it may be too late to try them this year. But at least you can see if thrips are the cause this time, so that you can remember to apply the systemic insecticide next May.