The lush grounds of Stubbings House near Maidenhead will be open to the public on Sunday to help raise funds for the Thames Valley and Chiltern Air Ambulance.
The air ambulance is a charity dependent on donations to keep flying.
It costs about £3m a year to run but receives no Government or lottery funding.
The 80-acre Stubbings estate in Henley Road will be open from 11.30am-4pm.
Maidenhead Concert Band will be playing from 2pm.
Stubbings is one of 70 locations supporting the air ambulance through the Open Gardens initiative.
Air ambulance spokesman Robert Downham said: "The Open Gardens scheme is very important, not just for fundraising but also for raising awareness.
"The generosity of the gardens is invaluable."
The ambulance has flown 300 missions since the start of the year, 28 of which were in Maidenhead or within a 10-mile radius.
Other locations will also be supporting the air ambulance through the initiative.
Park View and Queen Anne’s Ride gardens in Windsor will be open on June 26.
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