Answer: Your lilac hibiscus (also known as blue hibiscus) is not a hibiscus at all. It is a perennial plant from Australia where it thrives in hot, dry places. Botanically it is Alyogyne huegelii. Your plant is moderately frost tolerant but some protection is required from the heaviest frosts. Experience with growing this plant in California has shown that it can survive short periods of 20F without any permanent damage. The yellowing leaves are probably natural at this time of year. I'd cover it when temperatures dip below freezing and uncover it when the temperatures are above freezing. In the spring, after all danger of frost has passed, prune it back to encourage healthy new growth.
Best wishes with your garden!
Q&A Library Searching Tips