I take green thumb because I like to turtle and create just one uber level five city. After the latest patch which I have yet to play, I calculate I will require 8 villas and +60% in the houseing bonus tech. That means I need 8 food. Hmmm maby I could get away with no green thumb if I
enchant the city (would need to take the spell book) +1
build the farm +5
build the granary and irrigation +3 = +9
Hmm but with green thumb I can save 2 building squares and because its there from the start I can build huts right from the get go. Then there is the question of if the adventure tech will be kind enough to deposit the food resource it provides within the radius of a level four city's influence. This is good at least the game has me thinking about my choices... ooo almost forgot theres a good chance my daughter will have green thumb also which would help if I start popping out babies early, though that doesn't really come into the initial calculation and affect my game plan if I only build one city.