It might be interesting to add permissions for each plant or group of plants in order to set a different rate for them to be played without this permission :

Without permission:
WHEAT:
Growth: 65
Death: 5
Biome: []

With permission :
WHEAT:
Growth: 70
Death: 1
Biome: []

Can be added in the configuration a "group like BiomeGroup"

Permission1:
WHEAT:
Growth: 70
Death: 1
Biome: []

Unfortunately due to the way that crops grow, they aren't assigned to a "player" but rather to tick timers in the world when chunks are loaded... so, there is really no way to tie a set of growing crops to any specific player, atleast not in the general sense of the game.. if there are plots or regions that have a player owner it could be done then but that would require another plugin...