Looks like it’s 20 blooms daily per map (the chest with the cache in it) and then 5 per 10 stacks (5 at 1-9 stacks, 10 for 10-19 stacks), based on the reporting in the Reddit thread. It could additionally scale some other way; perhaps if the map gets a certain amount of invasions done the daily bonus is increased, who knows.
Regardless, the rewards are embarrassingly bad, especially given the lack of exp/gold/karma.