These are songs about or related to gardening, not songs that just happen to have a garden related word in the title.
The Anti-Garden Song YouTube A parody of "The Garden Song"
She Thinks My Tractor's Sexy YouTube Music Video by Kenny Chesney
Plant a Radish YouTube Amazon B000V8EECQ from the 1960 musical ‘The Fantasticks’!
Plow to the end of the row YouTube
I Don't Eat Animals YouTube Melanie Safka
Little Potato YouTube
Call Any Vegetable YouTube Frank Zappa
The Vegetable Song (Barnyard Dance) YouTube
Gardening Lyrics by Dillon Bustin Recorded by Malcolm Dalglish, Grey Larsen and Pete Sutherland on "Root Crops & Ground Cover"
Lists of Songs about Gardening
Folk Alley Blog post Song titles and some lyrics.
Secret Garden YouTube Instrumental Song from the Secret Garden