Types of Annuals
Annuals fall into a few broad categories based on their cold tolerance, a distinction that determines exactly when each type can safely go into the ground.
Hardy, Half-Hardy, and Tender
Hardy annuals, like pansies and snapdragons, tolerate frost and can go into the ground weeks before the last frost date. Half-hardy annuals tolerate a light frost but not a hard freeze, while tender annuals, like impatiens and coleus, are damaged by any frost at all and must wait until it has fully passed.
Knowing which category a plant falls into prevents the common mistake of planting tender annuals too early, only to lose them to a late frost.
Hardy annuals like pansies can even be planted in fall in many regions, overwintering to bloom again in early spring — well ahead of anything planted after the last frost.
Choosing by Bloom Habit
Some annuals, like sunflowers, bloom just once with a large impressive flower, while others, like petunias and marigolds, bloom continuously in smaller flushes all season — worth considering alongside cold tolerance when choosing what to plant.