Answer: The tropical hibiscus sold as patio trees need a full sun location and like a rich, evenly moist yet well drained soil. This can be a balancing act when they are grown in a container.
They also need regular feeding with a fertilizer formulated for flowering plants, read and follow the label instructions. Take care not to overfertilize and do not use a foliar feed when temperatures are high as you risk burning the plant. (This could cause leaf browning.)
Falling foliage can indicate transplant stress (if you just repotted them) or cold nights (surprisingly enough we have had a few recently) or overwatering (do not allow water to collect and then sit in a saucer under the plant) or underwatering (make sure the water is not running out between the soil and the side of the pot) or a pest problem.
These plants are susceptible to whiteflies and spider mites, especially in hot dry weather as we have been having. Whiteflies are little, white, flying insects and spider mites are very small insects that cause a stippling on the foliage and leave little dusty, webby deposits on the undersides of leaves or where the leaves join the stems. Spider mites are very common on these plants. If you suspect either of these, try rinsing the leaves daily -- top and bottom sides -- with a strong spray of water from the garden hose. If the infestation is very heavy, you could try either a commercially formulated insecticidal soap or a "summer" type of light-weight horticultural oil. Be sure to carefully read and follow the instructions.
There are a number of pests that may attack these plants, so if you suspect a pest problem you may want to take a sample to your county extension for a specific identification and specific suggestions as to how to control it.
Finally, I would really suggest you remove the beetle trap to avoid attracting more of them to the area. They seem to attract at least as many as they catch so do not really help in the long run. On a small number of plants, a quick session of handpicking in the evening or early morning when they are sluggish works equally well.
I hope this helps you trouble shoot.
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