Answer: Hibiscus syriacus is widely adapted, doing fine in soils with a range of pH from about 5.5 to 7.0. If you have one of these that is not flowering well, there are a couple of factors to look at. One possible cause is that a new plant will not bloom as heavily as an established one, it is using most of its energy to become rooted and established. They do well in average soil, so an excess of nitrogen could cause excessive vegetative growth at the expense of flowering. Using a complete granular or slow release fertilizer such as 10-10-10 in spring per the label directions should be adequate. You could also top dress with compost and of course, use an organic mulch. The mulch should be in a flat layer over the root area but should not touch the stem. Keep it about two to three inches thick. This will help feed the soil slowly over time as well as help keep weeds down and keep the soil moister. In drought conditions, flowering may be reduced. These are drought tolerant shrubs but new plants would still need an evenly moist soil (not saturated, just damp) for the first year while they are becoming rooted and established. Next,these shrubs need full sun all day or for at least a half a day including the hour of noon so if it is in shade it may need more light. Next, they begin blooming in summer and continue for quite a long time, so it may not have peaked yet. Lastly, pruning at the wrong time will limit flowering. These shrubs bloom on new growth of the season, so the best time to do any needed pruning is in late winter to early spring. At that time remove any winter damaged stems and also reduce size if desired. Pruning in summer will remove the flowering wood. I hope this helps you trouble shoot.
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