Most rock gardens or wall plantings include perennials. However, a number of annuals can also be incorporated to provide season-long color.
According to Utah State University Extension horticulturist Jerry Goodspeed, there are a number of annuals that thrive in dry, hot locations and add interest to a rock garden.
"Dahlberg daisies have very fine foliage and are normally covered with yellow blossoms that look similar to miniature daisies," said Goodspeed. "They often struggle in a pony pack or in small pots, but as soon as they get their roots in the ground, they take off, covering a large area in as little as a month."
Another low-growing annual with yellow flowers is sanvitalia. It is often mistaken for a smaller black-eyed Susan because of the brown centers in blossoms.
Sanvitalia has been marketed as creeping zinnia because it has a zinnia-like blossom spreading habit.
A little more aggressive than the Dahlberg daisy, sanvitalia fills in an area much quicker, though its foliage is slightly coarser.
Although verbena is common in hanging baskets, the annual also makes an attractive addition to a rock garden, said horticulturist.
Verbena produces a multitude of blossom colors from vivid pinks and purples to white and peach hues.
The plant often has an attractive white eye in the flower's center.
Verbena spreads its wispy foliage as it sweeps over rocks and other plants without shading them out.
"One plant normally noted for wrapping around things is the true morning glory - the annual flowering plant, not the pesky weed," noted Goodspeed. "Although this vine is a climber, it can also trail over and around rocks. With its large pink-to-blue and white flowers, it is aggressive enough to cover a large area by the end of the summer."
Sometimes gardens need more upright plants for interest and to vary the elevation of a bed.
One plant that easily accomplishes the objective is the amaranthus.
Grown for its colorful foliage and seeds, the amaranthus comes in red, yellow, green and white.
Some varieties grow tall and attract attention, while other smaller varieties add interest without becoming the focal point.
Another more upright annual that tolerates a dry, rocky environment is the globe amaranth, said the USU Extension horticulturist.
The purple, red and white flowers resemble a large clover flower.
One advantage to globe amaranth, also called gomphrena, is that the plant does not need to be deadheaded.
Globe amaranth flowers also maintain color for extended periods so they are often used in dried arrangements.
"Other annuals for rock gardens include annual vinca, nasturtium, portulaca, and salvia, which all do well in hot, dry environments," said Goodspeed. "This is a good time to add them to your rock garden so you can enjoy their color for the remainder of the season."