Britain's Prince William watches as his wife Catherine, Duchess of Cambridge, shovels dirt during a tree planting ceremony at Rideau Hall in Ottawa July 2, 2011. Also pictured are Canada's Governor General David Johnston (R) and his wife Sharon (2nd R). Prince William and his wife Catherine, Duchess of Cambridge, are on a royal tour of Canada from June 30 to July 8. [Photo/Agencies]

OTTAWA, Ontario -- Prince William and Kate have started the third day of their Canadian tour with a tree-planting ceremony at Government House that has become a royal family tradition.

The Duke and Duchess of Cambridge each wielded a shovel Saturday as they planted a Canadian hemlock, an evergreen tree known for its longevity.

The royal couple, who married on April 29, then chatted with Canadian couples celebrating their 50th and 60th wedding anniversaries.

Prince William's parents, Prince Charles and Princess Diana, and his grandmother, Queen Elizabeth II, planted trees on previous visits at Rideau Hall, the official residence of both the Canadian monarch and Governor General of Canada.

The royal couple flying later to Quebec for a two-day stay, where protests by French-speaking separatists are expected.