Authored by Carol Shirk, Certified Master Gardener
Photo credit: C. Shirk
While perennials, annuals, and biennials all have a place in the home landscape, nothing beats annuals for season-long bursts of color in a bare space. With careful consideration, matching the plant to the space, these plants can thrive in a multitude of light and soil conditions.
Perennial are plants that grow for a minimum of two years, but more likely grow for many more. Generally the top part of the plant dies, but the roots persist and a new plant regrows from that root. Biennials require two seasons to complete their life cycle. The first season growth is a small rosette of foliage at soil level. During the second season, the stem completes its growth and the plant flowers, produces seed, and dies.
Annuals complete their entire life cycle from seed to flower to seed again in one year. Therefore, these must be planted each season. A true annual, like a sunflower, will not continue the life cycle beyond a year regardless of the environment. However, some plants are considered annuals in Wisconsin because of the cold winter. In their native environment, they are perennials. For instance, Geraniums (Pelargonium) are perennials in their native Southern Africa, while Dusty Miller (Senecio cineraria) is a perennial shrub in the Mediterranean.
Annuals are exceptionally diverse. Color and texture of both foliage and flower, plant size and adaptability to nearly any growing conditions run the gamut in annuals. There are hundreds if not thousands of species and cultivars available, many of which are suitable for growth in Wisconsin. They will provide the grower with a season-long display of color as well as ample food for a score of pollinators. However, planning is paramount in the use of annuals since they must be planted each spring and cleaned out of the landscape beds each fall.
As with nearly anything a gardener plants, the first course of action is a soil test. This all-important test evaluates nutrient level, organic matter, soil acidity (pH) and gives recommendations for improvement.
Annuals can be used in a variety of ways. A full bed of annuals is always an option; draw a plan, keeping in mind the mature height, light and water requirements of each plant. Mass plantings of one species or color is an eye-catching display. Do not plant most annuals until danger of frost has passed. Purchase healthy looking plants, none with yellowing or drooping foliage. Carefully remove them from the pot and gently tease the roots apart before planting them no deeper than they were in the nursery pot. Water carefully and thoroughly to give them a good start on their summer long journey.
An alternate use of annuals is place them in a perennial bed to fill in the gaps where early summer blooming plants are finished for the season or in front of those late fall plants to have some color before they start their bloom time.
Annuals also make stunning container gardens. When assembling a container, keep in mind the “thriller (tall), filler, spiller (cascading)” rule to make an eye appealing display.
For a great list of annuals that will flourish in Wisconsin gardens, please see the following website: https://hort.extension.wisc.edu/article-topic/annuals-selection/page/2/ Each entry has a description of the plant plus the necessary growing conditions.
Certified Master Gardener