Fourteen species of orchid are known to grow at the reserve including some of the UK's rarest species. Park Gate Down is one of only three sites in the UK for the nationally rare monkey orchid (Ochis simia). The orchid was introduced to the site during the twentieth century from another Kentish site and has since flourished with over 100 plants. Park Gate Down also supports the nationally rare late spider orchid (Ophrys fuciflora) that in the UK is limited to the North Downs in East Kent as well as the nationally scarce lady orchid (Orchis purpurea) and musk orchid (Herminium monorchis) of which 72 were counted in 2007.