There is a particular pleasure in starting seeds: part anticipation, part faith. You are planting something in a small amount of compost and trusting that several weeks later it will have become a plant. For the medicinal herb grower, this act carries additional resonance. The seedling nursing on a windowsill in March will be in your apothecary jar by September.
What to Start in March
Calendula is one of the best herbs to start from seed in March, either under cover for early plants or direct-sown once the ground is workable. It germinates reliably at relatively low temperatures and grows quickly. German chamomile can also be started in March, though it does well direct-sown in April. It needs light to germinate (do not cover the seeds) and prefers a temperature around 15 to 20 degrees. It self-seeds so generously that once established you may never need to buy seed again.
Holy basil (tulsi) needs warmth to germinate well (minimum 20 degrees, ideally 25) and is best started under cover with some bottom heat in March. It is worth the effort: tulsi is one of the most beautiful plants in the medicinal garden and one of the most useful herbs in the Ayurvedic tradition.
Ashwagandha can be started from seed in March under cover. It needs warmth (around 20 degrees minimum), does not tolerate root disturbance well (sow directly into the final pot size if possible), and needs a long growing season. Start it now.
Valerian germinates best in cool conditions with some light, making March under-cover sowing ideal. Fresh seed produces considerably better results than seed stored for more than a year.
What to Wait On
Basil is better waited on until April or May. Lavender, rosemary, and thyme are most reliably propagated from cuttings rather than seed, as seed-grown plants are highly variable. If you want plants this year, buy well-grown plugs from a specialist herb nursery.
The Basics of Germination
Most medicinal herb seeds need adequate moisture (not waterlogging), the right temperature range for the species, and appropriate light or dark conditions. A heated propagator on a bright windowsill covers most requirements. The Herbalist Codex app includes growing notes for individual herbs covering germination requirements and what to look for as the plant develops. The seed packet is where it starts.