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An annual may be defined botanically as a plant that completes its entire life cycle within the space of a year: it grows, flowers, produces seed, and then dies, regardless of temperature or other environmental conditions.
Gardeners, however, do not use that definition in defining annuals and perennials. From a gardening standpoint, an annual is usually defined as a plant that dies because it is unable to survive extremes of cold or heat, that, the winter is too cold or the summer is too hot — and that is what I mean when I use the word "annual" in this book. When a typical garden annual, such as geranium or a petunia, is grown in a greenhouse, it will flower and produce seed many times over, surviving for years.
The difficulty of the gardener's definition of annuals is obvious: winters and summers vary depending on latitude and altitude. Is an annual in Duluth still an annual in Miami, even though it survives winters perfectly well in Florida? Or conversely, will a perennial in Fargo be a perennial in New Orleans even though it dies because of summer heat? For better or worse, I have made an arbitrary decision as to what most people accept as a garden annual. Using the USDA hardiness zone map as a guide, I consider all plants that are "usually" killed by winters in zones 1 to 7 (global warming and recent mild winters notwithstanding) annuals. That includes all Canada (except its west coast) and at least three-quarters of the land mass of the United States. According to the USDA zone map, winter temperatures in zone 7 (the southernmost zone in my definition) range from 0 to 10 degress Fahrenheit, although most annuals die when sustained temperatures of 20 degrees Fahrenheit are experienced.
Other plants, commonly used as winter annuals in southern zones, are later pulled out because they cannot tolerate warm summers. These same plants may be fine summer annuals in cool summers. Such a group would include pansies, violas, English daisies, pot marigold, snapdragons, and hybrid pinks (the Appendix includes a list of these winter annuals as well.) Gardeners in the southernmost areas of the country, in such gardening oasis as Houston, San Diego, or Key West, may find this book more useful as a guide to perennials rather than as a guide to annuals. No matter what we call thses wonderful plants, let's enjoy the beauty they provide.
