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USDA Plant Hardiness Zone Map—About the Map |
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Basic Plant Requirements Were Considered First
All agriculturists, environmentalists, horticulturists, and home gardeners have one all-abiding question about any plant they wish to introduce into their growing spaces. Will it flourish?
The ability to predict whether a newly collected species or cultivar can be successfully grown in a location is fundamental to the continued productivity of America's agriculture and to the survival of our landscapes. The plants in our urban spaces, farms, fields, and forests consist of native vegetation and exotic plants introduced into our land from all over the world.
All plants must be placed in an environment that meets their basic requirements:
Day length. Day length is usually the most critical factor in regulating vegetative growth, flower initiation and development, and the induction of dormancy. Plants survive only when the day length promotes their growth and prepares them for the seasonal changes.
Radiation. Most plants respond to radiation in the 270- to 3000-nm region. Cloudy, rainy days coupled with the shade provided by nearby plants and structures can significantly reduce the amount of radiation available. Plants survive only where the amount is within a specified range.
Temperature. Plants grow best within an optimum range of temperatures; and the range may be wide for some species, narrow for others. Plants survive only where temperatures allow them to metabolize.
Frost. Plants differ in ability to survive frost, their responses varying from immediate death to sustained performance. The previous environmental and cultural conditions of plants can often shift, but not permanently alter, their tolerance to freezing. Plants survive only when they are adapted to subfreezing weather.
Heat. The thermal cutoff temperature varies widely from species to species. By tradition we group plants into sun, partial sun, and shade types and plant them according to their light and heat tolerances.
Rainfall. Gardeners need to know how much water a landscape plant requires in determining its usability in low maintenance landscapes. Rainfall gardening often greatly limits which species can be used successfully. Gardeners also need to know how much and how often to water plants in high maintenance landscapes.
pH. The ability of plant roots to take up water and nutrients depends on the pH (measure of acidity or alkalinity), presence of soluble and insoluble salts, and aeration of the growing medium. The successful culture of all plant species requires that they be grown in a medium within a definite pH range and with from 10 to 14 essential nutrients in appropriate balance. Although plants may tolerate some extraneous elements and compounds, every plant species and cultivar has well prescribed limits.
USDA Miscellaneous Publication No. 1475, Issued January 1990