Trees should be covered while in transport if they are not dormant, and protected from extreme heat or cold. How the trees are to be unloaded needs to be specified, and anything that damages the roots, main stem or larger branches should be disallowed. It takes a number of years for a tree to become established on a site after transplanting. Tree have basic requirements for survival just as people do. Air and sunlight are sometimes less than desirable in cities, but are usually adequate for growth.
Urban soils are usually very compact and lack air space and organic matter.
To improve their condition, a large portion of the existing soil must be replaced. Incorporating improved soil in a planting pit slightly larger than the root ball is no longer an acceptable planting method. New construction projects should require that the entire area between curb and sidewalk be replaced with topsoil to a depth of at least two feet. Adequate drainage must also be assured. The major problem with water is supplying enough for survival during times of drought.