The architectural design for the house was executed by Harold Peto and Sir Ernest George; Peto, with Emma Henderson, designed Sedgwick's Italianate garden with its large sweeping terraces of sandstone, a beautiful sunken pond and large open walkways lined with colourful herbaceous borders. The garden has a nautical theme, with areas being named the White Sea, the Upper Deck, the Bulwarks, the Captain's Bridge and the Cabin.
The Gardens have been featured in Country Life Magazine no less than five times between 1901 and 1957. The view from the house to the South Downs and Chanctonbury Ring is still as tranquil and beautiful as it was when Sir Neville Henderson, son of Robert and Emma, wrote of it, "I know of no more satisfying view in all England. Water and wood, the green expanse and the radiant flower-bed, the dense hedges of yew and the waving beauties of undipped trees, all play their part in the beauties of these gardens". Emma Henderson's brother, Reginald, married Alice Liddell, the young girl that Charles Dodgson (Lewis Carroll) took as his model for Alice in Wonderland. Alice and Reginald spent their honeymoon at Sedgwick in 1880, and she wrote of her time at the house as "I think Sedgwick will be a long time before it shelters two more foolishly happy creatures than Reginald and me".
Further developments occurred in the garden in the Fifties, under the care of Lord Rotherwick. It was under his guidance that a stream was created, with 21 small inter-linking ponds flowing into a magnificent cascade at the end of the formal gardens.
The following decades saw a period of decay for the garden and house. The herbaceous borders were lost, as was a lot of the garden statuary. Formal yew hedges grew misshapen and monstrous, and weeds grew in the once well-tended terraces. Fortunately the current owners are restoring it to its former glory, and the gardens are starting to regain some of their beauty.