Annual plants complete their lifecycle in one growing season. Familiar annuals include Petunias, Marigolds, Impatiens, Million Bells, and most of the showy, long blooming plants that we use in our hanging baskets and patio containers. Because they live for only one season, annuals put all of their energy into producing abundant flowers from spring through fall. Annual plants must be planted each spring (“annually”). Just to confuse the issue, many plants treated as annuals in Wisconsin are actually perennials which are not cold hardy enough to survive winter here. Examples include Guara, Mandevilla, and Rosemary.
Biennials are plants that complete their life cycle in two years. The first year they produce only foliage, usually low to the ground. In their second year of life they grow to their full height, bloom and produce seeds. If allowed to self-sow these plants will produce seedlings and persist in your garden from year to year. Since seedlings will decide for themselves where to grow and might not come up exactly where the gardener desires, biennials are best suited to a cottage garden or informal flower bed. Familiar biennials include Hollyhocks and Foxglove.
Perennials are plants that survive in the garden for multiple years. Some live for decades while others may live only 3-5 years. Because perennials need to devote energy to root development, they cannot use all of their energy on flowers and therefore bloom for a shorter time than annuals. Most perennial bloom for 3-4 weeks but some particularly long blooming ones may provide as much as 8-10 weeks of flower color. Familiar perennials include Peonies, Daylilies, Hosta Iris, and Coneflowers.