He said heritage roses belong to 16 families. Their names trip off the tongue - damask roses, China roses, musk roses, moss roses. They are very fragrant, can be as big as trees and have more subtle colours than their modern relatives.
His favourite is Souvenir de la Malmaison, named by a Russian duke after the garden of a French woman he was in love with - a more romantic name than the modern Sexy Rexy.
"For as long as humans have walked this Earth, they have walked in company with these roses," he said.
Not for much longer perhaps. In 1995, there were more than 1300 heritage roses available to buy. Now there are fewer than 600, and Tasman Bay Roses is the last specialist nursery.
Heritage Roses New Zealand aims to keep at least one plant of each variety growing for posterity. They have combed the South Island for them so far. Wanganui was Mr Radka's last stop in the North Island.