|I have 12 Hibiscus plants all in sun. Some bloom, some drop off yellow leaves and now some have holes in their leaves. They are all taken care of in the same manner. I live in the perfect climate for these plants (all are outside).|
There are three species of Hibiscus, but judging from your region, you're probably growing the Chinese Hibiscus (Hibiscus rosa-sinensis). This is the tropical looking evergreen with large glossy leaves and large red, white or pink flowers. All Hibiscus require full sun, good drainage, regular, deep watering and frequent feeding.
If you prune the plant in early spring, you'll encourage new flowering stems. If you pinch out the tips of the new growth in the late spring and early summer, flower production will increase. When you water, apply liberally to wet the entire root system. Feed plants every two weeks with a diluted liquid fertilizer (from spring through the end of summer), pinch out the the tips of the new stems and your plant should produce blooms. Yellowing leaves might indicate the growing conditions are not quite right, or your plants could just be shedding some of the older leaves. Holes in leaves can be from environmental problems such as windy conditions that injured the leaves or leaf buds, or there may have been insects snacking on the leaves. I'd prune the plants back to encourage healthy new growth, then feed and water regularly to maintain health.