To be held at The Royal Geographical Society on Tuesday 27 October 2015, London tickets for the event cost £20 with all money raised from the evening being donated to the National Gardens Scheme.
NGS chief executive George Plumptre said: "We are delighted that Alan has accepted our invitation to be the guest speaker at the first ever National Gardens Scheme Lecture. The Royal Geographical Society auditorium provides a suitably grand venue for such a well loved and respected gardener, broadcaster, author and entertainer to entertain and delight his audience.
Titchmarsh said: "During the course of the evening I will give guests an insight into my life and career. From the lad from Ilkley who went to work in the local nursery aged 15, to my time spent studying and working at Kew Gardens and then onto a career as a broadcaster, author, horticulturist and designer. But above all the immense amount of enjoyment and fun that I get from sharing with others my great passion for gardens and gardening.
"The National Gardens Scheme is unlike any other charitable organisation in the world in terms of the sheer number and diversity of gardens which open for it. I particularly like the Scheme as it offers visitors the chance to see the gardens of people who not only care passionately about gardens and gardening but also want to help raise funds for some truly great charities."