Answer: According to a Clemson University Web site on propagating hardy hibiscus:
"Seed can be sown indoors 12 weeks before the last spring frost. Soak seeds in very warm water for one hour before sowing. Seed can also be sown in place outdoors after the last expected frost date or fresh seed can be sown in fall. Collect seed for fall sowing once the papery seed capsules brown and start to split. Plants often bloom from seed in their first year and will often self seed in suitable soil conditions."
I hope this helps!
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