Donald Ziraldo co-founded Inniskillin Wines with Karl Kaiser in 1975 in Niagara-on-the-Lake. They had met the previous year, when Karl, a winemaker and chemist, purchased some grapes from Donald who owned and operated Ziraldo Nurseries. The two shared a vision of producing better quality Canadian wines and formed a partnership with Kaiser making the wine and Ziraldo serving as company president. In 1975, they were granted a winery license by the LCBO, the first one granted since 1929. Ziraldo has been called one of the founding fathers of the Canadian wine industry, and it is widely acknowledged that both men played a large role in the success and growth of the Canadian wine industry.
Ziraldo has been involved with numerous wine and grape related organizations and causes including those that relate to agricultural land, wine and grape research, environmental impact, and sustainability. He was influential in bringing together Ontario wine and agricultural land issues and making these known worldwide.
One of his roles was as a member of the Greenbelt Advisory Task Force. The Greenbelt Task Force examined the issue of preserving green spaces and managing urban sprawl. Their recommendations guided the government's approach to greenbelt protection in the Golden Horseshoe and helped to preserve agriculture and natural resources.
The Donald Ziraldo fonds contains extensive information on his involvement in agricultural issues, including the Greenbelt Task Force.