Traditional formalism of planting design within landscape architecture has two central faults; the objectification of plants and a focus on visual perception. This thesis proposes the correct appreciation of planting design is an aesthetic of engagement founded on interaction with the sublime in nature. Plants are the materiality of nature and design seeks to engender a phenomenological experience of landscape perceived through a series of events or encounters with the sublime. The aesthetic of engagement in planting design is articulated in four ways; direct engagement, indirect engagement, ethical engagement, and therapeutic engagement. Examples from contemporary projects verify an aesthetic of engagement for planting design. This thesis fills a gap in knowledge by providing a philosophical conceptualization of the aesthetics of planting design and a language through which to carry on dialogue over its presence. / The formalist tradition -- Sublime foundations of contemporary planting design -- The aesthetics of engagement -- A concluding example. / Department of Landscape Architecture