It is sometimes a problem to find an annual that likes hot dry places, especially sites adjacent to concrete, which reflects heat. A good edging plant, and one that thrives in window boxes, hanging baskets and places that need a summer groundcover, is "Portulaca grandiflora." It requires almost zero maintenance and flowers happily until frost in a variety of cheerful colors.
Cutting back the plant to half its size and giving a bit of fertilize will, however, provide a mid season impetus for additional blooms.
Moss Rose, as it is commonly called, is a native of Brazil, and the flowers open in the sun and close in the late afternoon. Space the plants 6-12 inches apart, or closer if you want a dense mat.
The Moss Rose Family
Pigweed is a far less admirable member of the Portulaca family, but none of us want that unfortunate plant in our garden, of course.
The Moss Rose branch of the family was introduced to Europe in the 1700's and rapidly gained high status because of its decorative and medicinal attributes. It was used for scurvy and muscle spasms.
A German legend relates how an angel, walking in a forest, became tired and rested under a rose tree. Upon awakening she thanked the tree by spreading a carpet of moss to keep the tree roots cool. This is the origin of the name.