There has been a garden at Knole for 500 years, ever since the days of Archbishop Bourchier, who created a small medieval lavender garden and an orchard near to the house. In the 16th century, under the ownership of Henry VIII and, later, during the tenancy of the Lennard family, this was extended and the Kentish ragstone walls, which run for almost a mile around the 24-acre garden, were added. Punctuating the walls is a series of wrought-iron gates, mostly dating from the time of the 6th Earl at the end of the 17th century. Through these gates are views out of and into the garden.

Then, as now, the garden was divided into a formal area, with lawns and borders and an informal area known as the Wilderness (mentioned by Lady Anne Clifford in her diary in the early 17th century), where mossy paths wind their way under the beech trees. Like the park, the Wilderness was devastated by the storm of 1987. This area of the garden has been replanted, too - to a design which respected the spirit of the past. Several of the avenues, which had been created towards the end of the 17th century by the 5th Earl, were retained.

Leonard Knyff and Jan Kip's bird's-eye view engraving in Britannia Illustrata (1707), shows a formal walled garden which was laid out in squares and rectangles, primarily as orchard. The royal gardener George London supplied fruit trees in 1698 and may have been responsible for the design. In 1709 the 1st Duke turned to a Westminster gardener, Thomas Ackers, who seems to have introduced the considerable changes visible in Thomas Badeslade's view of 1719. Badeslade records an oval bowling green with topiary arbours to the south of the house and a complex parterre to the east. In the early 18th century a Dutch canal was built where the sunken pond is (now a swimming pool). Hot-houses for growing pineapples were built beside the chapel in the late 18th century during the time of the 3rd Duke. Seats and a small summer-house were added in the early 19th century (around the time the Orangery was created) and the rhododendrons, the knot garden and some of the herbaceous borders date from Victorian times.