What is the main purpose of pruning in landscape horticulture?

Pruning is primarily performed to rejuvenate older plantings and promote balance within a plant’s structure. This process involves selectively removing specific parts of a plant, such as branches or stems, to enhance its overall health and appearance. By trimming away dead or overgrown parts, pruning encourages new growth, allowing sunlight and air to reach more parts of the plant.

Additionally, pruning can help to establish a balanced shape, which is essential for not only maintaining the aesthetics of the landscape but also for the plant’s vitality. When a plant is well-shaped and healthy, it is more capable of flourishing in its environment, leading to improved flowering, fruiting, and overall resilience against diseases and pests.

In contrast, eliminating colorful foliage would detract from the plant's visual appeal, promoting root growth is less directly linked to pruning, and increasing water retention isn’t a primary goal of pruning. Each of these other options does not encapsulate the essential and beneficial aspects of pruning that contribute to the health and structure of landscape plants, which is crucial for effective landscape horticulture practices.