[1] Among his best-known gardens are Iford Manor, Wiltshire; Buscot Park, Oxfordshire; West Dean House, Sussex; and Ilnacullin, County Cork, Ireland.
He was the son of a prosperous builder, engineer and railway-contractor, Samuel Morton Peto, of Somerleyton Hall in Lowestoft, Suffolk, and of Sarah Ainsworth (née Kelsall), his father's second wife.
Somerleyton Hall, where Harold spent his boyhood, had been rebuilt in the 1840s in Neo-Renaissance style and had a large winter garden and a parterre designed by William Andrews Nesfield.
He made Iford his permanent base, for which he re-designed and expanded the garden, trying out new ideas, and incorporating the artefacts collected during his travels around the world.
He also designed a series of gardens in Mediterranean France – at Cannes the Isola Bella, and at Cap Ferrat the villas Sylvia, Maryland and Rosemary.