Lachlan Rae from Scotland's Rural College won the Scottish final. Guy Jones won the Wales/Midlands final. The national final will be at the John Innes Centre in Norwich on 10 May.
Vandenburg, 26, has a botany degree from University of Guelph in Canada. She said she wants to work at Wisley or a botanic garden. "I've always been interested in plants," she said.
The South East runner-up was Tottenham Hotspur FC head gardener Gavin Hardy. Third place went to Kew diploma student Alex Hankey. Also taking part were Chris Pattison (Merrist Wood/The Outdoor Room), Lizzy Mills (National Trust Woolbeding Gardens), George Douglas (Capel Manor/Kew) and Billy Stott (Hadlow College).