You can use dawn if you are rehydrating old soil. So if you had like some pots with some old dried up root balls sitting around. Then yes, you can use dawn. A drop or 2 per gallon of water. However I would not recommend using dawn while in bloom. Dawn will kill some of the microbiology when you first apply (they bounce right back in a couple days) and you dont really want that 2 weeks into bloom. But if you got plants growing you would be better off using something plant based, Yucca, Aloe, or Quillaja Saponin Extract. I like the Q and Aloe. Thats not to say that if you have none of these that a Dawn cant work in a pinch. It just isnt my first choice.