When did Gregor Mendel begin his major pea-plant hybridization experiments?

In 1854, Abbot Cyril Napp authorized Gregor Mendel to plan a major experimental program in hybridization at the monastery. Following this authorization, Mendel spent the period from 1854 to 1856 testing 34 varieties of garden peas to ensure the constancy of their traits before beginning his formal hybridization experiments.1