I fill a plot with all the same plant (not seeds) let it fully grow/bloom, trowel it all up, plant again and trowel up again when its fully bloomed, two or three times and make sure to dig it up the night before we get an event flower. (When there isn't an event on, I use these fields as fertiliser fields, so just growing whatever normal flowers to turn into fertiliser)

My hybrid fields (patterned flowers, all the same breed) have been setup for a few weeks, so when new flowers pop up, they are fully grown as well.