Mildred Rushby, who died last December, left £115,000 after being a life-long supporter of the gardens and a leading member of the Friends of the Botanical Gardens for many years.

Her donation will be officially announced next Friday evening by curator Ian Turner at a preview evening of Art in the Gardens.

Mrs Rushby, who lived close to the gardens and was in her late eighties, worked tirelessly behind the scenes and was a regular fixture at its many plant sales.

Sue Kohler, chairman of the Friends' group, said: "Mildred always said she was going to leave something in her will for the Botanical Gardens but we never had a clue it would be so much.

"It really is fantastic news for us and we're working on ways to spend the money that will leave a lasting legacy to a lady with such immense passion for the Botanical Gardens."

Tickets for the preview evening – which starts at 6.30pm – are sold on a first-come, first-served basis and are available at £6 per adult from Margaret Howsham on 0114 250 0500.

Art in the Gardens opens to the public on Saturday and Sunday, September 6 and 7, from 10.30am until 5.30pm each day. Admission is £5 for adults with accompanied children free.