For 31 years, from 1959 to 1990, she was joint head gardener with Sibylle Kreutzberger at the garden at Sissinghurst Castle in Kent that was created by Sir Harold Nicolson and his wife Vita Sackville-West. During that time, visitor numbers soared from 6,000 per year to more than 170,000.
Schwerdt was on the RHS Floral A Committee (now Herbaceous Committee) from 1977 to 2008 and the Floral Trials Subcommittee (now Floral Trials Assessment Panel) from 1979 to 2009.
Schwerdt studied at Waterperry School of Horticulture, then taught there for eight years.
She was awarded the RHS Associate of Honour in 1980 and appointed MBE in 1990. In 1992 she was was co-recipient of the third International Carlo Scarpa Prize for Gardens awarded by the Fondazione Benetton. In 2006 she was awarded the Victoria Medal of Honour by the RHS.