Soak cranberry hibiscus seeds overnight before sowing. Remove and discard any nonviable seeds that are floating on top. Drain the remaining seeds on a paper towel.
Choose a planting spot in full sun. Work 6 inches of compost into the top 12 inches of soil with a tiller or turning fork and rake smooth with a garden rake.
Sow seeds on top of the ground 4 inches apart. Gently push the seeds into the ground with your finger to a depth of about 1/4 inch.
Water the area lightly daily until the seeds sprout and have two true leaves. Water twice a week until the plants are 6 inches tall. Water once a week thereafter if there is not an inch of rain. Thin plants to 12 inches apart when they are 2 inches tall.
Fertilize 4-week-old plants with an all-purpose granular or liquid fertilizer. Fertilize once a month thereafter. Add 3 inches or organic mulch around the plants once they reach 9 to 12 inches in height.
Pinch the top out of the plants once they reach 6 inches in height to encourage branching. Continue to pinch branches as needed to produce the bushiness you desire. Unpinched branches can become unruly and unattractive. Clip seed pods off as they dry, but before they open, to prevent invasiveness.
Cut your cranberry hibiscus plants back to the ground in the fall in temperate climates. Cover with 6 inches of light mulch, such as pine straw, for winter protection. Remove the mulch in the fall when all danger of frost has passed. Start fertilizing your plants once they are 6 inches tall.