Experts and BHG readers answer.
No Blooms on Geraniums
It sounds as though your plants have geranium budworms, also known as tobacco budworm. Because the worm quickly tunnels into the flower bud, few insecticides are effective in controlling it. Synthetic pyrethroids such as permethrin, cyfluthrin, or bifenthrin are the most effective controls. Also, ivy geraniums tend to be less susceptible to geranium budworm feeding injury.