How many plants should I have in my size area? It depends on the size you are ending with and the genetics of the plant you are growing. This is one you will have to judge for yourself. A common rule of thumb is: 4×4 Tray: 8-15 Plants. 4×8 Tray: 14-30 Plants What causes pH fluctuation and how do I fix it? I have yellow spots on the leaves, what is this?