Annual plant species are widely grown for the bold splashes of color they add to a garden; they are available as hardy, half-hardy or tender varieties. Hardy annuals are cold-tolerant, half-hardy tolerate light frost and tender annuals do not tolerate freezing temperatures. Annuals complete their life cycle within a single season.
Growing annuals means giving your plant the attention it needs to successfully complete a life cycle with vigor for a successful addition to your garden. Grow annuals in full sunlight, preferably with a minimum of four to six hours of daily exposure for optimal flowering. Annuals prefer well-drained soil and thrive in amended soil with the addition of pine bark or compost, particularly if you have sandy or clay soil with poor drainage. Additionally, maintain a pH level of 5.8 to 6.5. Add mulch to the bed surrounding your annual plant for weed control and moisture retention.
Ornamental kale (Brassica oleracea) from the oleracea species of Brassica, also referred to as flowering kale and ornamental cabbage, is a hardy annual that displays an open rosette of leaves in greens, reds, blues and whites. Often used as edging, this annual plant displays the most vibrant colors when kept in temperatures under 60 degrees F, according to the University of Florida IFAS Extension. While many annuals cannot thrive in colder temperatures, this hardy plant is well-suited for planting in any USDA hardiness zone and survives in temperatures as cold as 5 degrees F, according to the University of Illinois Extension. Ornamental kale reaches a height of 6 to 12 inches and width of 12 to 18 inches.
Sweet alyssum (Lobularia maritime) is an annual from the maritime species of Lobularia. This half-hardy annual plant displays an abundance of small pink to white flowers that emit a honey-scented fragrance, according to the Washington State University Clark County Extension. Sweet alyssum bloom from May to September and tolerate partial sun. With a spreading habit, this low-growing annual plant grows up to a height of 1 foot and a width of 2 feet. Plant in USDA Hardiness Zone 1.
Vinca (Catharanthus roseus) is an annual from the roseus species of Catharanthus. Vincas, also referred to as Madagascar periwinkles, are tender annuals that tolerate poor soil conditions, high temperatures and drought, according to the Clemson University Extension. Displaying an abundance of flowers in a wide array of colors including white with pink centers, apricot with raspberry centers, lilac, white, pinks, roses, purples and red, vincas bloom from June until first frost. Habits are varied including creeping vincas and dwarf cultivars. Often used as a border plant or planted in containers, vincas grow to a height and width of 1 to 2 feet, though spreading varieties remain closer to the ground and cover a broader expanse. Plant in USDA Hardiness Zones 9B to 11.
Depending on the species and the cultivar, annuals are susceptible to a number of disease and pests. When possible, plant disease or pest-resistant species for greater growth success. Avoid overhead irrigation as excessively wet sites can cause decay and fungal infections. Additionally, keep your garden free of weeds as they often act as hosts to insects that will move to your annual plants, according to the Clemson University Extension.