Limperts academy do one through griffith college dublin and also by distance. But i though it was a bit pricy when i checked it out. www.nightcourses.com
has a few on it
The limperts academy garden design course is one of the best going, and would definatly recommend it. Check out their own website
As far as I'm aware they use other colleges around the country for night courses - terenure college being one.
Sarsie, why do you say Limperts are the best going, is this personal experience?
Teagasc run a part time on in Blanchardstown which I haven't heard anything about, otherwise they run their general full time horticulture courses in the botanic gardens.