In most parts of the country, deep summer is when residential gardens are at their best. Well-watered lawns are lush and green, vegetable plots are thriving and annuals in flower beds, hanging baskets and containers.In the American South, however, the warmest part of the summer is also the most lackluster simply because many blooming annuals can't stand the heat. Impatiens, fuchsia and snapdragons, for instance, will simply burn up and die if exposed to high temperatures for more than a day or so. Fortunately, there are annuals that thrive in summer heat that can help keep Southern gardens looking vibrant. Following are five of them:

Cosmos

Native to Mexico, cosmos are well-acclimated to hot weather. They come in white, all shades of pink and deep scarlet. They grow to about four feet tall, making them a great option for the back of the border in most situations. They grow very easily from seed and self-seed themselves once established in the garden.

Sunflowers

As their name implies, sunflowers are sun loving plants that perform well in hot climate conditions. They come in cream, all shades of yellow and deep mahogany. They're one of the few plants that are tall enough to put behind cosmos in the back of the border. Like cosmos, they readily self-seed, but most bird species as well as their human counterparts love to snack on the seeds. Be sure to save some seeds in a cool, dry area to plant next year. 

Zinnias

Zinnias feature daisy-like blooms on long, sturdy stems, making them ideal for including in household bouquets. They come in all colors except for blue and are ideal for including in a mixed border. Although zinnias are very easy to grow from seed, and they're F1 hybrids, the offspring from the seed they produce won't be true to form, so you'll have to buy new seed every year. 

Portulaca

Otherwise, known as moss rose, portulaca is a low-growing little plant with a delicate appearance that belies its toughness. It comes in all colors except for blue and is ideal for rock gardens, the front of the border and planters. Another F1 hybrid, portulaca won't come true from its own seed.

Petunias

Petunias are suitable for almost any garden situation, but where they really shine is when they're brimming over in a hanging basket. These aren't easy to grow from seed, so most people purchase them in four-inch pots at their local nursery. They come in all colors but blue.

Plants that are acclimated to hot weather also tend to be drought-tolerant, which means you'll probably save a little on utility costs. As another added bonus, the above annuals are all fairly resistant to pests and diseases.