Answer: Without knowing which type of hibiscus you have it is a little difficult to answer your question. The tropical hibiscus (H. rosa sinensis) shrubs often grown as a container plant bloom on old wood, so you would want to prune them back in late winter then allow them to grow vigorously throughout the summer to encourage blooming; give them warm temperatures and full sun, evenly moist yet well drained soil, and regular fertilization with a water soluble or slow release product formulated for container plants.
The hardy Hibiscus syriacus shrub (sometimes called Rose of Sharon) also blooms on new growth of the season, so again the time to prune -- if needed -- is in late winter to remove any winter damage, then encourage it to grow vigorously for the summer and do not prune it once it has started to grow for the year. Use a general purpose fertilizer such as a granular or slow release 10-10-10 per the label directions in early spring and/or a topdressing of good quality compost. This plant needs full sun and a well drained soil. Overfertilizing or pruning at the wrong time can reduce blooms.
The perennial hibiscus plants such as H. moscheutos need full sun and very rich, moist soil to perform their best. If this is the kind of hibiscus you have I would suggest making sure it is well watered, fertilize in spring and again in early summer, and also apply a top dressing of compost and/or well rotted manure each spring. Mulch heavily in the late fall, then pull aside the mulch in the spring to allow the sun to reach the soil and warm it up as quickly as possible so the plant emerges a bit earlier in the season.
I hope this helps you trouble shoot.
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