Annual Flowers

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.

For window boxes and porch boxes, for potted plants on the terrace or on the low coping of a wall, for the indoor window garden, and for winter bloom in the small greenhouse the annuals can hardly be equaled.

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.