Very interesting. I did some testing with this on each stage out of boredom. I consider the tactic to work when the turnips land on solid ground, and when you can spawn multiple turnips for an extended period at a time.
Always works: Battlefield, Jungle Japes, Gerudo Valley (when the bridge is there), Yoshi's Island, Unova Pokemon League (when Zekrom doesn't tilt the stage), Flat Zone 2, Tomodachi Life, PAC-MAZE
Works on some transformations: 3D Land, Golden Plains, Rainbow Road, Prism Tower (works on all with platforms), Arena Ferox (works on all with platforms), PictoChat 2 (works on all with platforms), Wily Castle
Never works: Paper Mario, Spirit Train, Dream Land (there's one cloud transformation where you can get 1-2 turnips but it's negligible), Corneria, Mute City, Magicant (can only be done when there's both a mobile sprout/tree on the stage as well as the moving platform underneath = not really useful), Reset Bomb Forest, WarioWare, Inc., Distant Planet, Tortimer Island, Boxing Ring, Gaur Plain, Balloon Fight, Living Room
N/A: FD + For Glory stages, Mushroomy Kingdom, Find Mii, Green Hill Zone
I also tested some other things. Turnip farming while bigger or smaller (through mushrooms, lightning, etc.) will not affect the size of the spawned turnips. They'll still stay the regular size.
You can also turnip farm with light turnips and heavy turnips. The spawned turnips will retain the special properties. However, with both you can only spawn a max of 3 turnips on the ground at a time.