Annual Flowers: Flower Types

Is it an Annual, Biennial or a Perennial?
Local climatic conditions, development of new cultivars, and new uses for specific garden flowers have blurred the distinctions among annuals, biennials, and perennials. Annuals have traditionally been referred to as plants that complete their life cycle in one growing season. Some perennials that bloom quickly (verbena, Jerusalem cherry) are grown as annuals and discarded at the end of one season. Some of our so-called annuals (begonias, impatiens, snapdragons) are actually perennials in warmer climates or mild winters.

New cultivars of plants traditionally referred to as biennials are being developed that produce flowers the first season. Foxy is a cultivar of foxglove that will bloom the first year. Annual cultivars of sweet williams and hollyhock have been developed.

The distinction between perennials, flowering bulbs, and wildflowers is also blurred. Some garden books and magazines list flowering bulbs as perennials. Many of our wildflowers are commonly grown in perennial gardens, some are grown from bulbs.
Most annuals are planted in the spring, flower through the summer and fall, and then die with the first killing frost. Winter-flowering annuals, such as pansies, violas, and flowering cabbage, are planted in the fall, flower in the winter and early spring and die during the summer.

Types of Annuals
Annual flowers differ in their tolerance to cold weather and frost. Hardy annuals are the most cold tolerant; they will take light frost and some freezing weather without being killed. In most cases, hardy annuals can be planted in the fall or in the spring before the last frost date. Hardy annuals include calendula, cornflower, foxglove, larkspur, pansy, sweet alyssum, stocks, viola, and many dianthus cultivars. Most hardy annuals are not heat tolerant and usually decline and die with the onset of hot summer temperatures.

Half-hardy annuals will tolerate periods of cold damp weather, but will be damaged by frost. Most half-hardy annuals can be seeded outdoors in early spring since they do not require warm soil temperatures to germinate. Seeds or plants are normally planted after the last spring frost. Examples of half-hardy annuals include baby’s breath, bells of Ireland, blue sage, candytuft, celome, forget-me-nots, love-in-a-mist, snow-on-the-mountain, strawflower, and torenia. Many half-hardy annuals decline in the midsummer heat but may rebloom in late summer or fall.

Because most tender annuals are native to warm tropical regions of the world, they are sensitive to cold soil temperatures and are easily damaged by frost. Most seeds will not germinate well when soil temperatures are below 60°F. If the soil is cold, seeds will rot instead of germinating. Wait two to three weeks after the last spring frost to sow seeds or transplant outdoors. Tender annuals include ageratum, balsam, begonia, celosia, coleus, globe amaranth, impatiens, marigold, morning glory, nasturtium, nicotiana, petunia, scarlet sage, verbena, vinca, and zinnia.

Annuals are sometimes categorized as cool- or warm-season. Cool-season annuals, such as geranium, petunia, and snapdragon, grow best when the temperatures are in the 70’s and 80’s during the day. Best flower production is in the spring and fall; flower production declines in the middle of a hot summer. Warm-season annuals, such as blue daze, four-o’clocks, and pentas perform well when the day time temperatures are in the 80’s and 90’s and the night time temperatures are in the 60’s and 70’s.

Biennial flowers
The life cycle of biennial plants is completed over two growing seasons. During the first season they produce only leaves—usually in a rosette. Following a winter cold period, they flower in the second growing season, produce seeds, and then die. Popular biennials include foxglove, hollyhock, stocks, and sweet williams. Cultural practices are basically the same as for annuals, except that the plants are alive for two growing seasons.

Biennials present the obvious disadvantage of producing only foliage the first year. One solution is to sow biennial seeds in mid-summer so that the plants will develop during the summer and fall. After exposure to the winter cold, they will develop flowers in the spring.

Prepared by: Erv Evans, Consumer Horticulturist