Most scalp treatments are liquid, like the DIY tisanes or birch water. I used to apply them with my fingers but it was messy and I had a hard time doing the back of my head. Then I remembered how a girl I knew a long time back had done it. She was applying a solution of apple cider vinegar and water to help against dandruff.
You take a cotton pad, a small sponge, or even a small rag. You dip it into the solution and systematically apply onto the scalp, squeezing lightly. I like to do my hairline first, then part my hair inch by inch. Don't forget the back of the head and behind the ears!
Another alternative is to transfer the product into a small spray-pump bottle. These are usually available in DIY stores, you can save bottles from used-up cosmetics. I have also spotted Dr Hauschka pump tops which fit over their bottles. It is important that the pump is just right, some shoot out an annoying jet while other shoot out a very fine mist, you want something in between.
The third option would be a squeeze bottle, but here it is really hard to find something that will work with liquids. They work best for oils.
How do you apply hair treatments? Do share.