The impatiens are either suffering from some type of fungal stem and/or root rot. Watering them often really increases these disease problems. There are fungicides that can reduce these problems but proper watering is usually sufficient.
If disease did not cause the problems it may have been due to some insects chewing the stem or roots. A close examination of affected plants should indicate whether rots or insect chomping is the cause.
Bougainvilleas drop foliage when they go through a period of dry or soggy wet conditions. However they will normally go through cycles when they bloom or drop blooms. Their bloom cycle lasts a little over a month. After this the blooms or bracts fall off and the plant cycles through a period of a 6-8 weeks during which it grows leaves and shoots but not blooms. Then it will often enter another bloom period.
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