The 14 June all-day event (10:30 to 16:00) will include a private tour of the Elizabethan house and walled gardens, a silent plant auction, coffee on arrival and a two course lunch in the Tithe Barn, with an after-lunch talk by Titchmarsh.
Plant Heritage chief executive officer Sarah Quarterman said: "Alan is really passionate about the importance of the conservation work that we do here at Plant Heritage, so it is a real pleasure that he is attending and supporting our summer garden party."
Titchmarsh said: "I have always loved Surrey and it is a great pleasure to be visiting to support a particularly special charity, which is close to my heart. As the president of Plant Heritage, I have the pleasure of meeting many people with the same passion as me – to help preserve and protect garden plants for future generations to come. I hope to see many gardening enthusiasts at Loseley Park on the 14th June."