Mr Dowdeswell said Karen Craig, who will direct the performances of Macbeth, approached the trust wanting to celebrate the 400th anniversary of Shakespeare's death by staging a play at the gardens.
"We thought that was a good idea, so we thought we'd have a fair at the same time.
"We decided to make it Elizabethan to carry over the theme from the play," Mr Dowdeswell said.
He said the purpose of the fair was to attract people to the Bason Botanic Gardens.
"They're a real asset to Whanganui, but because they're a little way out of town people don't stumble across them by accident.
"The gardens are a great family environment, and we want to encourage families to come along and have some fun."
This is the first year the Great Bason Fair has been held, but Mr Dowdeswell said he hoped the event would become a regular on the Whanganui calendar.
-The Great Bason Fair, 10am-4pm, February 14, Bason Botanic Gardens, Rapanui Rd. Tickets at the gate, adults $10, under-15s free. Macbeth, February 12 at 7.30pm, February 13 at 2pm and 7.30pm, Bason Botanic Gardens. Tickets $20 from the Royal Wanganui Opera House.