[PhilD]

Only recruit Gardeners; until 4 turns before the end, another Gardener staying on a city pays for himself by sitting there, so recruit plenty of them.

There isn't much room for non-optimal play, though. I just played it again (on Legendary: 14 turns for 55k), and ended with 58200 on turn 14 - probably not the best possible, but close enough, I'd say.

Edit: 58200 wasn't optimal. 61800 is better... though I cannot beat it in 13 turns, it seems.