Engineering uses of plant materials on a residential site include controlling erosion, directing pedestrian and vehicular circulation, and screening glare from reflective surfaces.
Controlling Erosion Plant materials can be used on steep slopes or areas of loose soil to minimize erosion. Ground covers and plants with dense root systems are especially valuable because their roots hold the soil in place. The vegetative cover of plant leaves also protects slopes from the potential damage of precipitation striking the ground and from the eroding effect of blowing wind. Plant materials can be used on
loose soil or slopes up to 2:1 or 50 percent in steepness. Even plant materials have limited usefulness in preventing erosion on slopes that are steeper than this.
Directing Circulation Plant materials can be used as walls to direct how and where people and vehicles move on a residential site. One good application of this is along the front entrance walk leading from the driveway to the outdoor entry foyer. A mass of low plants can contain people on the walk as well as reinforce the direction of movement (Figure 11—47). A similar use of plants is along the driveway to keep vehicles on the driveway surface (Figure 11—48). However, plants should not crowd the driveway in such a way as to hinder the opening of car doors, or the removal and piling of snow in northern climates.
Screening Glare Plants can also minimize and screen glare from reflective surfaces. One way is to shade reflective surfaces such as cars or water. Glare is eliminated when the sun cannot strike the reflective surface directly. Glare can also be screened when plant materials are placed between the reflective surface and the viewer (Figure 11—49). One possible application of this is the placement of a low-to
medium-height hedge between a swimming pool or large panel of glass windows and an outdoor sitting space.