The secret gardens, along with the rest of the grounds, date back to the 11th century when the property was a monastery.
As per the name, any further history regarding the gardens remains unknown

The Barons Hall was built in the 15th century as Osney's Abbey's Bailiff. This was the finest period of Weston Manor Hotel when it owned much of the land in Weston On The Green. Barons Hall stands as a mark of power and the influence it once had in one of the oldest buildings in Oxfordshire.