The day has been chosen to commemorate the 77th anniversary of the Battle of Arnhem (17-26 September 1944) as one of the local military connections which prompted the orchard planting.
Covid-19 has prevented an official ceremony since 75 trees were planted in March 2020 to commemorate the 75th anniversary of the end of WWII.
Benches have since been installed with information boards explaining Grantham's role in WWII milestones, including the iconic 617 Squadron Dambusters Raid co-ordination from nearby St Vincent's Hall and D-Day American action from giant airfields around Grantham.
Another board illustrates the local build-up and training of airborne troops before their assault on the Rhine bridges immortalised in the film A Bridge Too Far - with a Visitor Centre display by the Barkston Heath Research Group.
More than £15,000 was raised through crowdfunding co-ordinated by South Kesteven District Council, which leases the land from the National Trust and itself contributed £5,615.
Cllr Annie Mason, SKDC Cabinet member for People and Safer Communities said: "This is a long overdue opening for a beautiful orchard and we are incredibly grateful to everyone who contributed to make it a reality.
"The orchard is a long-term project but we are looking forward to events such as apple days and community involvement in the future.
"We are hoping that individuals, businesses and schools who donated and planted trees can come and see how well it's developed as a living tribute to British forces and our wartime allies."
Ian Simmons, Chair of the Wyndham Park Forum whose volunteers care for the orchard, said: "I think people will be delighted at how well these trees have grown. The orchard has created an amazing public open space and an information and education tool for important events that we should take pride in."
The Visitor Centre will be open from 10am-4pm, with the official opening at 1.30pm.