I made this for Zoneark because he wanted it then people started asking me for it so I'm releasing it here.
Basically you make a small cone, hit with wrench, close the gui then type /grow, it then 'grows' by a 1x1 flat round every 45 seconds until it reaches $Plant::MaxHeight.
I'm not sure if the findGreen() will always come out green on all paint packs.
To make the max height different change $Plant::MaxHeight.
Have fun
Put this in your add-ons folder:
Script_Grow.cs