fuck these stupid employees, help if you can

ok i have my full set up and for some reason i am still getting blue star quality sometimes and where i give them the exact amount of fertilizer for each plant, and each pot, and most of the time i get purple star, but i have to sit at the barn playing quality control to pick out and trash blue star quality, and its starting to piss me off, my theory, that the plants are growing so fast and the employee is so slow they put on the fertilizer too late making it blue and not purple