Answer: The shrub hibiscus or Rose of Sharon (Hibiscus syriacus) tends to seed about on its own to the point of being a pest in some cases. An exception to this is some of the newer varieties which were bred to prevent this and do not set muvh if any viable seed. These can be started indoors in the spring or can be direct seeded in the ground either now as soon as they are ripe or next spring.
The perennial types of hibiscus can be started from seed also but in many cases the named varieties do not come true to the parent. You might be happier using divisions (spring) or even tip cuttings (summer) to propagate these. If you want to try the seeds, they would be handled as for the above. A soil temperature of about 70 degrees is best. With the perennials, since they start into growth so late in the spring, in my experience it is better to start them indoors and then plant them out in late spring to early summer once the soil has warmed up. Germination is usually quick and they do not require chilling or special treatment.
Good luck with your hibiscus!
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