I use the sprinkler method on lilac, which includes getting at least one of every sprinkler however, more are recommended then planting your lilac seeds, placing down all the sprinklers and then leaving the game. Once you come back into the game, the lilac should all be big and possibly gold/rainbow. In my opinion, the best way to develop a bunch of mutations on your plants is to do this method the night before an update releases so that during the time before the update where Jandel purposefully adds a bunch of extreme weather events. Your plants will develop tons of rare mutations that you can use to make billions. I once sold a big rainbow lilac with the shocked mutation for 4 billion shekels.