When to Put Out Annual Flowers

Types of Annuals

• Annuals can be basically grouped as either cool-season or warm-season types. Cool-season annuals tolerate light frosts or brief freezes and prosper when temperatures don't get much higher than 75 degrees Fahrenheit. By contrast, warm-season annuals do not tolerate any frost, and tend to grow quickly and look lush when it's warmer than 80 degrees. Most annuals would in fact be perennials in the right climate; they would persist indefinitely if frost, heat or drought didn't kill them off at some point during the year. Impatiens, coleus, pansies and lantana are examples.

Warm-Season Annual Planting Time

• Warm-season annuals like marigolds, petunias, coleus and impatiens are planted or set out in the outdoor garden when there is no further threat of frost in spring. The last expected frost date varies by latitude and elevation across North America. Gardeners in New Orleans may set out warm-season annuals as early as late March, while in Chicago the last frost threatens until early May. Some warm-season annuals are only planted when the soil warms to above 65 degrees Fahrenheit, which is late spring or early summer in some locations.

When to Plant Cool-Season Annuals

• Light frosts and temperatures as low as 25 degrees Fahrenheit don't faze cool-season annuals like pansies, violas, ornamental kale, calendula, wallflowers and snapdragons. These plants prosper in the cooler days and chilly nights of both spring and autumn. Plant cool-season annuals as soon as the soil can be worked in spring in the northern United States; in the South you can plant them in early spring or mid-fall. In fact, in mild winter climates, cool-season annuals often persist through and bloom in winter.

Precise Timing

• The geography of North America is varied, so it's difficult to provide a precise month or date when it's safe to set out annual plants for all locations. Find out when it will be time to plant at your local plant nursery. Ask staff members for advice and recommendations for planting your annuals. The most reliable and precise gardening information, including annual planting times, is provided by local county Cooperative Extension Offices in the United States.