Severn Sea
Rosemary in the US

Rosemary seeds need a bit of warmth to get them going, so starting indoors is your best bet, especially if your growing season is shorter. Sow them shallow, just a quarter-inch deep, in seed trays or small pots filled with good seed compost. Keep them nice and warm, around 65-70°F (18-21°C), on a sunny windowsill or with a heat mat if you have one. Germination can be a bit slow and patchy, so don't give up on them. For zones 5-7, April or May is a good time, but check your local last frost date and the GrowMore CookMore app for precise timings in your USDA zone.

Once your seedlings are big enough to handle – they'll have a few true leaves – carefully prick them out and pot them up into individual small pots. Give them a bit of time to grow on indoors, letting them get sturdy. Before planting out, you'll want to harden them off over a week or so, gradually getting them used to the outdoor conditions. Plant them out after all danger of frost has passed, spacing them about 18 to 24 inches apart, or pop them in a nice big container if you're short on space.