Answer: Hibiscus may stop blooming for a number of reasons. One is lack of light, although in your case that doesn't sound like the problem, at least not in the summer. These plants are heavy feeders so I suspect that the soil needs to be renewed and if the plant has grown a great deal the pot may simply be too small. Hibiscus should cycle in and out of bloom all year, with the heaviest blooming in spring and summer. (Sometimes you can trick them into better blooming in the winter by adding artificial light for 14 to 16 hours a day.) Tomato fertilizer seems to work well for these plants.
Interestingly enough, most of the plants are treated with a growth retardant to keep them compact. Once that wears off ( a year or so later) the plants grow in their normal somewhat rangy style. Some gardeners will work at the plant regularly, pruning one larger branch at a time, thus not removing all of the blooming wood at once. Otherwise, early spring would be the best time to cut it back, both to encourage branching and shapeliness and to control size. This would also be a good time to repot into a larger pot or to root prune and replant into the same size pot.
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