19th century and later

A portion of the Aldridge estate was sold in 1801 to Charles George Beauclerk, who erected a house called St Leonard's Lodge on the site of the present mansion. The Beauclerk family were responsible for the first ornamental plantings at Leonardslee. By the early 1800s the denudations of the iron works had been replaced by more than a century of natural regeneration. The estate was now lightly wooded, mainly with oak, beech and chestnut, with some ancient pines and larch plantations, and in which there were a series of seven man-made ponds, some of which once provided power for the Wealden iron industry.^{[citation needed]} The gardens were established in 1801 and covered 200 acres 200 acres (81 hectares) in a steep sandstone valley.^[2] Charles Beauclerk included an American garden with conifers, palms and giant sequoia Sequoiadendron giganteum as well as planting the first camellias, rhododendeons and magnolias that suited the acidic soil.^[3]

In 1852 the estate was sold to the Hubbard family, specifically William Hubbard, who commissioned the present Italianate style house, completed in 1855, designed by Thomas Leverton Donaldson, the first Professor of Architecture at University College London.^{[citation needed]}

Victorian plant collector Sir Edmund Loder purchased the estate from his parents-in-law in 1889^[4] and planted extensive collections of Rhododendrons and Azaleas and many species of trees. Loder became interested in plant hybridisation and developed new rhodendron varieties, the Loderi hybrids.^[3] He planted a large amount of exotic flora in a short time and also introduced gazelle, beavers, kangaroos and wallabies.

A rock garden near the house was built c.1890 by the Victorian landscaping company James Pulham and Son,^[2] who also built a mound, using a mixture of natural and artificial cretaceous sandstone, containing artificial caves for mouflon, later used to shelter wallabies. It was planted initially with ferns and alpines organised by Loder. The Pulhamite rockery is among the most intact remaining in the UK in the twentyfirst century.^[3]

Parts of the gardens were used for filming several exterior scenes of the 1947 film Black Narcissus, which is set in the extreme north of India.^{[citation needed]}

In 1973 the main house, built in 19th-century Italianate style, and in 1980 a contemporary octagonal lodge to its north-west, were listed Grade II for their architectural merit.^[5][6] The garden is listed Grade I on the Register of Historic Parks and Gardens.^[7][8]

The last Loder to own Leonardslee, Robin Loder, made four new lakes and new plantings on the east side of the valley.^{[citation needed]} In February 2010 it was announced that estate had been sold by the Loder family to an international businessman and that, after the 2010 April to June season, the gardens would be closed to the public. The gardens closed on 30 June 2010.^[9] Before closure, Leonardslee also contained a collection of Victorian motor cars, a miniature exhibition called Beyond the Doll's House, and a display of modern outdoor sculptures, and attracted 50,000 visitors per year.^{[citation needed]}

The house and gardens were acquired in July 2017 by the Benguela Collection Hospitality Group, owned by the South African-based entrepreneur Penny Streeter. A plan was developed to provide restoration and maintenance over a decade. Overgrown trees were removed and lakes, glasshouses, infrastructure and buildings repaired.^[3]

It reopened to the public in April 2019.^[10][11] The Benguela Collection Hospitality Group is also the owner of Mannings Heath Golf Club & Wine Estate in Horsham, 3 miles (5 km) away.^[12]