Hi
sibyl yes hardy hibiscus put on seeds.They will form a seed pod where the blooms drop off.
The seed pod will turn brown when there ready to
pluck from the plant get them just as they start to open so as not to lose any seeds.
When you start your seeds plant them 1/4 inch deep and keep them moist they should sprout for you in 7 to 12 days.most hardy hibiscus will grow 1 stalk the first year but may not bloom till the second year.Then the plant will come back with more and more stalks each year from the root system.
They love full sun and lots of water during the hot summer days.
Hope this helps and good luck on growing them.
Your friend in gardening. Mike57