Enchanted Shrubbery spawns on the North side of the Stone Hive Castle. Approx LOC is: p456, n93.
By killing the various shrubbery in that particular area (i.e. A Shambling Shrubbery, A Enchanted Hedgewalker, An Animated Vinewalker, A Sentient Growthspirit, etc...) will spawn the E. Shrubbery.
Sometimes it spawns back to back. Don't count on it though. Their spawn timer is approx 20 minutes. Be prepared to kill through several cycles.
If you don't want to mess with the Stone Hive faction you could kill them with a FD Necro directing a pet. That's what another person was doing when we showed up to kill it.