In 1890, Premier Oliver Mowat appointed Dryden Minister of Agriculture. As Minister, he oversaw reforms at the Ontario Agricultural College and was a strong supporter of agricultural training and instruction. He implemented a program of 'travelling dairies' whereby a portable horse-drawn dairy toured rural Ontario providing instruction to farmers. He also established dairy schools at Strathroy and Kingston. These measures were designed to improve the quality of dairy products produced in Ontario in an environment characterised by American tariffs and export challenges. Dryden remained minister through the governments of Mowat, Arthur Sturgis Hardy and George William Ross.