19 Plant Use Categories
Learning Objectives
- Describe horticultural plant use categories.
Horticulture production provides plant resources for a wide range of functional, cultural, and aesthetic garden purposes. Ornamental plants are used for environmental enhancement, food production, and re-vegetation of damaged ecosystems, as well as for their visual and sensory appeal in landscapes and gardens. An overview of the ornamental horticulture sector in Canada is available at this link to the Canadian Ornamental Horticulture Alliance [New Tab]. Some common categories of plant use include bedding plants and cut flowers, trees and shrubs, and ground covers and climbers.
Bedding plants and Cut Flowers
Bedding plants, such as Lobelia erinus (lobelia) and Petunia × hybrida (petunia) are grown in greenhouses and nurseries for seasonal interest in gardens and landscapes. They are typically tender and half-hardy annuals, biennials, and some perennials that grow quickly and provide a vibrant display of color in beds, containers, and hanging baskets. Cut flowers produced by the floral industry include both herbaceous and woody flowering plants and cut greens for specialty services.
Trees and Shrubs
Trees such as Acer rubrum (red maple) and Quercus rubra (red oak) grow from single stems while some like Acer circinatum (vine maple) have two or three main stems. This distinguishes trees from shrubs with several or many stems branching from or near soil level. Whether deciduous or evergreen, trees are generally larger than shrubs however, their shape and height can vary from dwarf cultivars 1 meter high, to grafted standards on 2 meter rootstocks and specimens of 90 meters or more. Tree selection must account for mature height and spread to ensure adequate space in the landscape. Trees with year-round interest in form, foliage, flower, fruit, and bark are commonly grown in open sites as specimen plants. They may serve as a focal point for an entrance or as a special accent in the garden. On large sites, trees are often planted in groups to form woodlands or hedging. Strategic planting of trees in urban environments can channel air movement, shade and cool microclimates, and provide barriers for noise and security, as well as frame or screen views.
Shrubs such as Cornus alba ‘Elegantissima’ (silverleaf dogwood) and Hibiscus syriacus (hardy hibiscus) are valued for their ornamental features and varied growth forms. Shrub sizes range from 0.15 meter to about 6 meters. Deciduous and broadleaf evergreens, variegated foliage, fragrant and showy flowers and fruits, as well as decorative stems and buds provide year round interest and variety in mixed borders and container planting. Shrubs are commonly massed for effect, planted in small groups in mixed plantings, or used as screens and hedging. The wide selection of shrubs produced by nurseries provides for most garden conditions.
Groundcovers
Groundcover plants such as Ajuga reptans (bugleweed) are adapted with creeping and carpeting habits and are often used under woodland and shrub plantings, and for covering and stabilizing some slopes. Plant runners (stolons) that root where they touch the ground and spreading underground stems (rhizomes) that send up new shoots and form colonies stabilize and cover bare soil reducing erosion, evaporation, and weed growth.
Climbers
Climbing plants, whether woody or herbaceous, deciduous or evergreen provide strong vertical elements and year round garden interest. Where space is limited, climbers such as Hydrangea anomala ssp. petiolaris (climbing hydrangea) may be the best option for screening and climate control. It is important to match the vigor, method of attachment, height, and spread of a climber with an appropriately sturdy support and adequate light exposure for flowering and fruiting.