Can I mix root organic with top soil?

I have a friend who threw his plant into my grow after he tried to sprout in mud. I transplanted it into some of my roots organic but don't want to use all my good stuff on someone else's plant. Can I cut the roots Organic with some all purpose topsoil to fill a 10 gallon bucket? I also have steer manure loaded with nitrogen. His plant is the small one in the very middle. I don't want to go out and buy anything so that isn't an option.