The event from the former Gardener's World TV presenter is "destined to be a practical celebration of Autumn gardening and the harvest".
West Country nurseries, celebrity speakers and practical demonstrations, local food and entertainments in a picturesque location will feature.
Buckland said: "I’m delighted to bring the GardenFest to Forde Abbey, not least because the gardens there are stunning in early autumn, with its aster-filled Herbaceous Border, beautiful trees and abundant Kitchen Garden which will make a spectacular backdrop."
Forde Abbey has been owned by the Kennard family since 1869 with current custodians
Julian and Alice Kennard the sixth generation to live and work at Forde Abbey. Alice Kennard said: "I’m very much looking forward to welcoming Toby and his team to Forde Abbey next September for an Autumn plant fair that celebrates the very best of what’s in season."
The first of Buckland’s Garden Festival took place at Powderham Castle and is returning for a fourth year in April 2017 as an annual festival. A festival at Bowood House ran in 2015.
Toby Buckland Garden Festivals are organised by Country Gardener Magazines.