I have had good success (about 3/4 or so) getting cuttings to root, both with and without rooting hormone - maybe a little higher with hormone.

I take the cuttings in June, usually late in the month, and cut them to about 8" long. I strip the bottom leaves and any blooms that may be present.

My rooting buckets are plastic 55 gallon drums, cut off about 14" tall, from the top and bottom. There are small holes, plugged with polyester fiber, about 2" up from the bottom, to prevent excess water from collecting and sand exiting. The buckets are located along the north wall of my garage, so no sun hits them.

I stick the cuttings into about 4" of play sand, in these buckets. I usually don't have to provide extra water, but do so if rain isn't regular. I do not cover the buckets after sticking the cuttings, they get adequate protection from the sides.

Cuttings are rooted in 4-6 weeks.

I have not made any serious attempt to grow Scarlet Hibiscus from seed, but others may want to comment on producing plants from seed.

I propagated this plant from seed this spring with fairly good germination. I did scarify the seed before I planted it by rubbing it with a file.