from what i could tell.. most recipes use heather, yarrow, mugwort, and sweet gale... sometimes mixed in equal proportions, and sometimes all equal except for the sweet gale.. i guess whats best for me is to study what each of these do and when to add them... then i could taste the product and see what needs to be adjusted.. so i think experimentation is best
im going to brew a very basic scottish wee heavy using golden promise and roasted barley as the only grains, and EKG or fuggles hops with scottish ale yeast... when i have this recipe tuned im going to remove the hops and start testing it with gruit
this one recipe i found for a scottish ale using gruit was 2 ounces of each mugwort, heather, and yarrow with just a dash of sweet gale, so i think ill grow these in a garden this summer to harvest for making an old fashioned medieval ale... in fact, my recipe is going to be very similar to the one here
http://www.gruitale.com/rec_st_emilian_gruit.htm except i will be using golden promise and roasted barley so i could follow the quantities and time for each step with my recipe... yeah, i like that idea, thats what ill do this fall and if it comes out well, i will have to determine how much of the herbs ill need to grow next year to satisfy my brewing habits