Perennial plants and flowers give a permanent shape to the garden landscape and annuals give spots of temporary color. The initial cost of purchasing perennials can be greater, but they also return each year in greater numbers. Annuals are sometimes used for a bright mass of color in the height of summer, while perennial blooms can be long lasting.
Annuals are plants that germinate, grow and die within one growing season. Annuals can be hardy, half-hardy or tender, according to their cold tolerance. Perennials are plants whose life cycles are longer than one season. Some perennials, such as verbena and Jerusalem cherry, bloom quickly and can be grown as annuals.
Hardy annuals include calendula, cornflower, foxglove, larkspur, pansy, sweet alyssum, stocks, viola and many dianthus cultivars. These annuals prefer cooler temperatures. Heat-loving annuals include marigolds, zinnias, Vinca, scarlet sage and petunias. Perennials differ in their heat tolerance. Candytuft and primrose thrive in cooler spring temperatures. Daylily, blanket flower and pentsemon bloom in hotter weather.
Most perennials prefer full sun. Choose delphinium, heliopsis or daylily for a bright garden location. Annuals such as nicotania, nasturtium and cornflower thrive in full sun, while annuals such as impatiens and viola grow well in semishade. Perennials that do well in hanging baskets include tuberous begonias and fuchsias. Petunias are a popular annual for hanging baskets.
Perennials sometimes need to be cut back in the fall when they go into a dormant period. Chrysanthemum plants wilt back after blooming and can be cut to the ground. Other perennials such as daylilies fade and lose some leaves but do not require cutting back. During the winter dormant period, perennials use their energy for root development. Perennials such as camellias do not go into a dormant period but remain evergreen.
Perennials need organic matter, such as compost, incorporated into the planting bed each growing season. When soil is amended with compost, the perennials have a good supply of nutrients for the next growing season. It also makes existing soil nutrients available. Annuals thrive with compost added at the beginning of the growing season. Perennials such as purple coneflower and hyssop can be given a side dressing of compost in the middle of summer to ensure a long bloom season.
Water-wise gardening is necessary in climate areas that receive little rainfall. Annuals such as creeping zinnia, cosmos, marigolds and dusty miller grow well under drought conditions. Perennials that do not need constant watering include yarrow, plumbago and periwinkle. Drought-tolerant perennial groundcovers include wooly thyme, iceplant and poppy mallow.