We have three potted Hibiscus plants (Tree style). Outside beside a fence in open but sheltered patio. All three are within 2 feet of each other. ONE plant is showing a few uniformly yellow leaves and then dropping them. Continues to have buds and a few blooms. Soil feels OK and we water all three plants the same. Plants are 30-40 inches tall in 24 " pots. Help !!
A great place to find solutions for Hibiscus problems is at the American Hibiscus Society board: http://www.trop-hibiscus.com/q.a.html They have a Q&A section that will answer most of your concerns.