my school put food coloring in when they grow some white flower, thay make em blue red purple all diffrent colors. they sell these flowers on holiday to make money for the school, the flowers looked healthy so i dont think the food coloring would harm the plants at all. the stuff to flavor the bud might be bad but i have researched this and supposedly it doesnt harm in any way here is a link on how to do it: Flavoring

what do you mean by "grow rock" could i just use some large pebbles?