I just grew a plant in Flower Town with 5 people contributing to blooming it. How many more do I need to harvest seeds and do favorite colors/plants they are growing also come into play?
It looks like the next time it is watered after blooming the plants will exchange pollen, creating seeds to be harvested. Each additional encounter will produce a seed until the plant has no more to produce.
Different plants bloom at different rates, so it can go from 3-5 watering to be partially to fully bloomed.