Frost-free climates
Plants for beauty: Seeds or seedlings of ageratum, alyssum, amaranthus, carnations, celosia, coleus, cosmos, dichondra, echinops, erigeron, gaillardia, gazania, gloxinia, gourds, hymenosporum, impatiens, nasturtiums, phlox, salvia.
Very hot and dry gardens: move a shade cloth to cover veggie and flower gardens now to shelter them from the worst of the heat, pull out tired plants that grew all winter, mulch and water twice a day if you have the energy. Concentrate on a few small bright patches of flowers rather than struggle with large areas.
Temperate
Cold
Plants for beauty (temperate and cold): Achillea, ageratum. alstromeria, alyssum amaranthus, aster, balsam bellis perennis, bells of Ireland, brachycome, calendula, candytuft, Canterbury bells, carnation, celosia, Clarkia, cleome, coleus, coreopsis, columbines, cosmos, delphinium, dichondra, echinacea, echinops, erigeron, euphorbia, foxglove, gaillardia, gazania, globe amaranth, gloxinia, godetia, gypsophila, helichrysum, heliotrope, hellebores, honesty, lavender, marigolds, nasturtium, petunia, phlox, Flanders poppy, portulaca, rudbeckia, salpiglossis, salvia, scabious, sweet William, viola, zinnia, snapdragons.