Both a landscape designer and a public artist, Ken Smith produces designs that range in scale from small public installations to vast parks. He is known for inventive and imaginative gardens and landscapes, some of which use little or no natural plant material. His projects include public, commercial, and private work: urban parks, streetscapes, plazas, gardens, public art commissions, memorials, museums and institutions, urban development and multiuse projects, restoration of modern-era landscapes, waterfront planning and design, and residential projects.

Among Smith's best-known projects are the MoMA Roof Garden, consisting of white gravel, recycled black rubber, crushed glass, sculptural stones, and artificial boxwood plants in a camouflage pattern; the Elevated Acre, a one-acre urban plaza with a sloping topography of planted dunes and an elevated view of New York Harbor; and Orange County Great Park, California, a redevelopment of a Marine Corps air station to include a 2.5-mile canyon, 20-acre lake, cultural terrace, botanical gardens, great lawn, performing arts venue, veterans memorial, aircraft museum, sports park, nature preserve, and wildlife corridor.