The Lib Dems are in control of 31 councils, with 62 MPs, 12 MEPs, and 4200 councillors nationwide.
The Greens are in control of zero councils (nearly the largest party in Norwich), with zero MPs, 2 MEPs, and 116 councillors (for England and Wales, plus 8 with Glasgow/Edinburgh councillors).
Now, consider that the Lib Dems only have 60 360 members, and the Greens (England and Wales) have 7440 members.
Either the Lib Dems are ultra-competent and ferociously disciplined, or there is a certain tipping point (Our first MP? 200 councillors? Control of our 1st council?) where you reach a critical mass of active members and you start achieving real electoral gains.