Raise your hands: who put their hibiscus plant outdoors for the summer and now it’s looking pretty sick with dropping leaves all over your floor?
It is probably a case of too little water, but increasing your watering schedule is not going to help. A hibiscus grows quickly during the summer, and the increased root mass displaces the soil in the container. The water — as well as the fertilizer you probably applied religiously every two weeks — is traveling straight through rather than soaking in. You pour water in, see it come out through the drain holes, and naturally assume that the hibiscus has been watered and fed. Unfortunately, the soil around the roots remains dry, and the plant remains thirsty.
Knock the hibiscus out of its pot and take a look. Overcrowded roots signal that moving to a larger container is necessary. When repotting, score the root ball with a knife or pull through the roots with a hand cultivator and tease some away so that they will grow into the fresh medium. If you don’t, the roots will remain would tightly, occupying the center of the container, and you’ll have the same starved, thirsty plant — just in a larger pot.
Of course, no matter what you do, a hibiscus will probably sulk in the winter. It is a full-sun tropical plant, and the low light, short days, and low humidity that come with spending a Northern winter indoors are even more depressing for it than for us.
One further note that may fall under the horticultural truth-in-packaging principle: small potted hibiscus, frequently sold in the spring, appear to be dwarf plants covered with large flowers. Most, however, are treated with a growth retardant to keep them small. When the retardant wears off after a month or two, the 2-foot plant is on its way to becoming a 6-footer. This can be disconcerting to anyone who has not seen the same phenomenon occur in a teenage boy.