The scheme will give the college a contemporary glass building which will house a science and technology centre, collections house, teaching rooms and project spaces and research and development facilities.
The college was successful in its bid for funding for the project from the Skills Funding Agency.
Principal Tamsin Jones said: "This is a fantastic milestone for us. Seeing the old buildings being knocked down marks the end of an era, but our students and staff are all so excited about the new redevelopment which is going to replace them.
"This stunning new building will ensure we remain at the forefront of the horticulture industry and our students will be able to learn using the latest technology, providing them with a competitive advantage when they begin their careers in the industry."
The new developments are due to be completed by September 2015. Current college activities and facilities for students will be unaffected during the works.