The Master Gardener program trains Cooperative Extension volunteers to provide horticultural education in their communities. Started in 1972 in King and Pierce counties in Washington State by the local horticultural Extension agent, Dr. David Gibby, this unique volunteer program has become internationally recognized and often duplicated as a model for other volunteer programs. Today, Extension Master Gardener (EMG) programs exist in all 50 United States and the District of Columbia. Most counties with a sizable population have EMG volunteers. As of 2005, approximately 90,000 EMG were active volunteers in the US and Canada, and probably another 100,000 trained volunteers had completed their volunteer service and joined the ranks of the inactive. From 15-20,000 new EMG volunteers are trained annually in the US, and waiting lists are not uncommon.

Approximately 2,557,792 hours of EMG volunteer work are completed annually. Using an economic value of $10-$17 per hour of volunteer work, the value of EMG volunteer work is $25,577,920 to $44,889,250 annually. If 5 people are assisted for every 1hour of EMG volunteer time, then 12,788,960 people are assisted by an EMG volunteers every year. This is equivalent to the population of Pennsylvania or Illinois being contacted annually by an EMG volunteer.

The Cooperative Extension Service conducts the volunteer training. Thus, the Extension information they receive and the recommendations they will make are university or research based. To assure volunteers are up-to-date, most programs have a structure for initial training and annual updates or advanced training that is a required of all volunteers. The initial basic training for EMG usually consists of 40-80 hours of classroom courses; in return, the participants give an equal number of volunteer hours during the next twelve months. Beyond the first year, annual volunteer expectations are usually lower, 20-30 hours, and the educational requirement still lower, approximately 5-15 hours of continuing, advanced or specialized training. Most programs distinguish between actively volunteering EMGs and those who are inactive and no longer providing volunteer hours. To remain “active” usually both educational and volunteer requirements must be met annually.