Trees, with their wide variety of species and shapes, are often described as being "hardy and tall". Hardy is a general term, meaning the tree is well-adapted to surviving the prevalent growing conditions, although this can vary greatly by region and elevation. Tall is an adjective that is more elusive, since it depends on reference. Generally, trees over 40 feet may be regarded as being tall.
What Is Hardy?
The term "hardy" is loosely applied to plants that are known to survive the prevailing growing conditions. Thus, "hardy" can be applied to a plant's ability to survive winter cold, severe drought, or even lack of maintenance by a garden caretaker. When generally encountered, a "hardy plant" means one that can handle the soils, rainfall and climate of a region. Resistance to pests and disease can also be included in the definition.
Hardiness of a plant can also be made more succinct in its definition in any defined geographical region. A plant can be considered hardy to usual growing conditions at sea level or in a local acidic soil, but merely 20 miles away, the same plant may not grow well and not be considered "hardy". Moreover, a plant can have multiple "hardiness" definitions--such as being "hardy to drought," but not "hardy to wet, cold winters."
What is "Tall"?
The adjective "tall" is subjective, even in horticulture. Generally speaking, however, trees that grow larger than 40 to 50 feet in height may be referred to as "tall." Some literature will be specific in how it defines tall, even going to far as to differentiate between "medium-tall" and "very tall."
Trees grown outside the confines of a conservatory or atrium will usually attain taller mature heights. Trees closely planted together will grow in a more upright manner in efforts to gain the best exposure to sunlight. This competition often finds woodland trees reaching very slender, tall heights in comparison to the same tree species if grown uncrowded in a spacious meadow or turfgrass lawn.
A hardy tall outdoor tree, regardless of species or region, is used primarily as a shade tree. However, any tree can also have the purpose of blocking wind or unattractive views. Many timber trees, used for paper or wood products, can be considered hardy, tall outdoor trees, too.
Plant Species Examples
In temperate regions of the world, common tall trees include maples (Acer), oaks (Quercus), fir (Abies), spruce (Picea), sequoia, and pine (Pinus). Within these cold-winter areas will be more localized plant species from native woodlands that may be favored, such as a magnolia, tulip poplar (Liriodendron) or cypress (Taxodium). These trees may be deciduous, losing their foliage in winter, or evergreen.
In tropical areas, common tall trees include fig (Ficus), teak (Tectona), baobab (Adasonia), gum tree (Eucalyptus), pine (Araucaria and Agathis), and mahogany (Swietenia). Palms are not botanically referred to as trees.
Contact your local cooperative extension office or university botany/horticulture office for a list of hardy tall trees for your region.