From the Latin annus, meaning 'year' - and that's how long these plants take to grow from seed, flower, have sex, make more seed and die. Annuals are great for creating instant effects.
Hardy annualsHardy-annuals such as corncockle love-in-a-mist and nasturtium can withstand the cold, so you sow them outdoors in spring: March or April. There's less work involved in raising them than with half-hardy annuals.
Half-hardy annuals Half-hardy annuals such as cosmos, petunia and salvia die if exposed to the cold, so they can't go into the garden until after the last frost. Sow indoors in spring. They'll keep going until killed by the first autumn frost.