Store your rose of Sharon seeds in an opaque, airtight plastic container after harvesting them in the fall or if you purchase them after the prime planting season in early spring. Store the container in a cool, dark place or your refrigerator.
Fill a seed flat with rich potting soil. Push your finger about a half inch down into each well, creating a small hole. Drop a single Rose of Sharon seed into each hole. Cover the seeds with soil and press down gently.
Water the seeds with about 2 tbsp. of water per seed well. Set the seed flat in a warm, sunny window or in a bright, warm greenhouse. Rose of Sharon seeds need no special care beyond warmth and moisture to germinate.
Water your seeds every three days. Seedlings should begin to sprout in two to three weeks after planting. When the seedlings reach about 3 inches, water them every five days or once a week.
Transplant your seedlings to pots or to the ground after they reach 10 inches or when spring has come with no more threat of frost. Plant them in full sun and in well-drained, rich soil. These conditions will help them thrive.