Plant annuals at the right season and in the right spot, and you can easily have months of glorious blooms. But, start a marigold too early, place a zinnia in a spot that’s too shady, or stick a begonia where it’s too dry, and you’ll get a quick lesson in the importance of understanding your garden’s climate patterns and other conditions. (Click here for climate in detail) This section looks at annual-specific climate issues.

To grow annuals, you don’t need to worry about your precise climate zone and temperature extremes as much as you do with permanent plants, such as perennials, trees, and shrubs. Annuals are more straightforward. You simply have to wait until after the last killing frost to plant.

Cooling Down, Warming Up

The first thing you need to know about any annual that you want to add to your garden is whether it’s a warm-season or a cool-season annual. The difference is vital to planting annuals at the right time of year in your area.

Cool season and warm season are, of course, relative terms. Where summers are cool, such as along the foggy California coast or other overcast climates, you can grow cool-season annuals all summer. Where winters are warm and nearly frost-free, such as in low-elevation Arizona, fall through spring is an ideal time to grow cool-season annuals, such as Iceland poppies and stock, and even some warm-season annuals, such as petunias. In fact, winter and early spring make up the main flower-growing season in Arizona — summer there is too hot to grow any annuals except the most heat-tolerant warm-season varieties.

If you live where summer gets hot, which is most of the U.S., plant cool-season annuals as early as possible (even before the last spring frost), and replace them after they fade in hot weather. If you live where summers are hot and winters are relatively mild (not dropping too far below freezing), you can plant these cool-season annuals in the fall, leave them over the winter, and they’ll bloom in early spring.

The Cool Cats

Cool-season annuals are those that perform best when temperatures are mild — about 70°F (21°C) — days are short, and soil is cool. In most parts of the United States and Canada, these conditions are typical in early spring and early fall. Temperatures may be similarly mild all season in mountain regions or in regions to the far north (or the far south, in the Southern Hemisphere). In some coastal regions, temperatures stay mild year-round. Cool-season annuals can stand varying amounts of frost; some types, in fact, are quite hardy and are actually perennials that live through the winter in many areas. The enemies are hot weather and long days, which cause cool-season annuals to produce fewer blooms and ultimately die. Examples of cool-season favorites are calendulas, pansies, and snapdragons.

You’re usually safe planting cool-season annuals a few weeks before the average date of the last spring frost in your area. If you live where weather is cool year-round or during the growing season, plant mostly cool-season annuals. If you live where summer days are hot and winters are mild, plant cool-season annuals in the fall for a winter garden.

In the typical cold-winter/hot-summer climate, the time to plant cool-season annuals is early spring — from four to eight weeks before the typical last frost or as soon as you can work the ground (dig and turn over the soil). Their season ends with the arrival of hot weather, when you can replace them with warm-season annuals. Where summers rarely heat up, many cool-season annuals can thrive all summer right alongside warm-season annuals that don’t demand hot weather.  ....read more