[Parasite]

This will not work for a 0% growth rate, but if you get at least one person a turn, try this....

Put different races from captures or trades on each planet. Each race will independently round up to add one person. An example being, put one each of 4 different O2 breathing races in a colony ship. The turn after the ship created the colony, you will have 8 people there. a 100% increase. 11 turns later you will have close to 50 people and after 24 turns you will get the first production bonus for breaking 100. If you have many planets, this can be used to accelerate pop growth almost more than the Organic buildings. If you have an example of 20 different species on one planet, you will increase the population of it by 20 a turn until the max of 100 is reached on a tiny planet. Breathing does not matter in this case. Note that rebellions (possibly Intel caused) will create new races which also will grow when spread around. This rounding effect is reduced as the population gets higher and the percentages of growth cause it to expand by one each anyway.