Environmental Requirements of Plants
In general, plants must be placed in an environment that meets their "requirements." These environmental requirements can be conveniently classified into "preferences" and "tolerances." Environmental preferences are those environmental conditions that are necessary for the healthy growth and productivity of the plant. Environmental tolerances are the environmental limits that can be tolerated by the plant. These environmental conditions include:
Light (sunlight exposure and day-length)
Most plants need sufficient light for vegetative growth, flower initiation, and the induction of dormancy. Sunlight exposure (sun, partial-sun, and shade) describes a plant's general sunlight and shade requirements. Some plants have specific day-length requirements. Plants adapted to tropical latitudes with fairly constant day-lengths (around 12 hours of light per day) are called "short-day" plants. Plants adapted to temperate latitudes with fairly large seasonal changes in day-length are called "long-day" plants. (Note: Recent research indicates that, in many cases, the "night-length" rather than the "day-length" may actually be the controlling factor).
Temperature (heat, cold, and frost)
Most plants prefer an optimal range of temperatures; the range may be wide, narrow, high, or low depending on the species. Some are susceptible to frost or cold damage while some require periodic extreme cold conditions. Plants are often classified by their cold and frost tolerances into "hardy", "half-hardy", "tender", and "very tender" types (see Plant Hardiness Definitions). Note: The sunlight exposure classification categories (sun, partial-sun, and shade) are actually rough measures of the combined light and heat requirements.
Water (rainfall or irrigation)
Some plant species require more water than can be supplied by local rainfall conditions some do just fine with little water (see Xeriscape -- coming soon) and some are easily drowned. Every species has their own water preferences and tolerances.
Though not strictly an environmental condition, all plants require a range of essential nutrients in appropriate balance and in sufficient quantities. Some nutrients (and even some otherwise extraneous minerals and compounds) can be harmful to plants in large enough quantities. (see Soil Fertility -- coming soon).
The ability of plant roots to take up water and nutrients depends on the pH (a measure of acidity or alkalinity) of the soil. Although the specific range of pH preferred or tolerated by different plant species can often vary, most plants are comfortable with a neutral to slightly acidic soil (pH: 7-6) and can tolerate a greater range if enough soil organic matter is present.