I would suggest the FPJ approach. I dug up a small plant, chopped it up, added an equal weight of molasses, and a shot of LAB to get it going. I let it ferment in a glass jar with an air lock for a week or two. Strain and use about a teaspoon per gallon.
Here is how I made a powder. This was more effort, but worked really well. Once dry I ran it throght a sieve and added it at about 1/4 teaspoon per gallon.