"The air was densely perfumed with a mixture of Victoria's scent (white heliotrope, from a shop off the Rue Saint-Honoré in Paris), potted jasmine and gardenias that stood about on every surface, apple logs in the grate and, on window ledges and tables, 'bowls of lavender and dried rose leaves, ... a sort of dusty fragrance sweeter in the under layers': the famous Knole potpourri, made since the reign of George I to a recipe devised by Lady Betty Germain, a Sackville cousin and former lady-in-waiting to Queen Anne."
From Behind the Mask: The Life of Vita Sackville-West by Matthew Dennison.
You can read a little about "the prim-looking" Lady Betty and her rooms at Knole - Vita's ancestral home - here, and this post apparently gives the recipe for the potpourri. Over here is another rather nice extract from the biography.