The site - which was once the kitchen garden that supplied fresh produce to the nearby Duncombe Park estate - has not been able to open to visitors so far this season and its manager feared it may never re-open again after losing a summer's worth of income.
But after a major fundraising appeal was launched, £50,000 has been donated to keep the gardens afloat and they will now re-open on August 1.
As the gardens do not open in winter, the money raised from individuals 'adopting' a square metre of the grounds for £25 each will keep the attraction solvent until March 2021.
Volunteer programmes for disadvantaged adults will also be able to resume later this summer.
The 18th-century gardens feature in the new film adaptation of the classic children's book The Secret Garden, starring Colin Firth and Julie Walters. Filming took place last summer after producers 'fell in love' with the gardens, but the movie's release date has now been postponed due to the closure of cinemas.
Garden manager June Tainsh said: “Local lady Alison Ticehurst restored the garden in 1994 from five acres of wasteland by the ruins of Helmsley Castle. It was heartbreaking when our stunning garden, made so by a small staff and essential volunteers, was blooming behind locked gates.
"The garden provides solace and a refuge for a great many of our 50-strong volunteer workforce - some of our more vulnerable volunteers are supported in a range of ways at the garden and the provision of this unique facility.”
The garden staff run a scheme whereby vulnerable people in need of mental health therapy can take part in volunteering activities.
The site is also home to a popular cafe called The Vinehouse, which is located in the old Victorian glasshouses where grapes were once grown. Run by twentysomething siblings Sam and Mollie Chapman since 2016, it was the only food and drink business in Yorkshire to win an accolade at the 2019 Visit England Tourism Awards.
The Chapman family also own Gepetto's, the Italian restaurant in Helmsley, but both businesses were forced to close indefinitely due to the lockdown. Sam and Mollie were unable to open The Vinehouse as planned this spring and it only trades during the gardens' seasonal opening.