Fill a seed tray with a light potting media, like a cactus mix or a combination of vermiculite and sand. Sow two or three rosemary seeds every 3 to 4 inches in rows. Cover the seeds lightly with additional soil mix.
Add water slowly to dampen the soil without displacing the rosemary seeds. Cover the seed trays with a cover or a piece of plastic wrap. This will keep the environment moist and encourage germination.
Place the seed tray in a warm location. Check the tray often and water as needed to maintain moist but not soaked soil. Look for rosemary seedlings to emerge in two or more weeks.
Move the seed tray to a sunny location and remove the plastic when the rosemary seedlings appear. Water the rosemary regularly to keep the soil moist.
Thin seedlings to one per spot, if more than one seed germinates in each location. Continue to grow the rosemary indoors until the plants reach at least 3 inches or more.
Transplant the rosemary seedlings into individual clay pots or directly into your herb garden outside to continue growing.