Is there a difference between hardy annuals and half-hardy annuals?

The Difference between hardy annuals and half-hardy annuals.

Hardy annuals can spend their entire life outdoors – from seed-sowing, right through to flowering. The seed can be sown outdoors in late winter or early spring.
Half hardy annual seeds will not germinate in conditions, so have to be sown in a heated place – Greenhouse, propagator, frame or indoors. (They then have to be hardened off before planting outside as young plants.

Most popular bedding plants are half-hardy annuals – marigolds, busy lizzies, salvias etc.

French Marigolds are half hardy annuals and have to be sown in warm conditions - normally a greenhouse or indoors on the windowsill and then planted out after all frosts have finished.

Calendula - the English or Pot marigold is grown as a hardy annual

Calendulas - or Pot marigolds - are hardy annuals, and can be sown directly into the soil - where you want them to flower. They will also re-seed themselves, so you will always have a display of this old-fashioned but fine hardy annual.