The couple - who have been dating since 2002 and got engaged earlier this year - want their upcoming nuptials to have a "green" feel.
Harrison said: "I haven't thought about greening my wedding. My wedding was always going to be green!"
The 'Indiana Jones' actor proposed to the 'Ally Mcbeal' star on Valentine's Day (14.02.09) while the pair were holidaying with Calista's adopted son Liam.
Last year, it was reported Harrison, 66, and Calista, 44, had discussed plans to marry and were keen to have a low-key ceremony attended by close friends and family.
Despite initially being reluctant to tie the knot again, twice-divorced Harrison - who has four children from his previous marriages - decided to commit to Calista in order to be a better parent to Liam.
A source previously said: "Harrison wants to give Liam his name. He adores him as though he were his own flesh and blood. Harrison is the only dad Liam has ever known.
"There is just one detail Harrison will have to take care of - marrying Calista. She says it is fine if Harrison adopts her boy, but she wants to walk down the aisle first."
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