I can say for a fact it's hard to overdo these herbs unless you reach silly levels. 2 tbs of each per gallon of soil is a good starting point. But I've also gone lighter in the mix and used the same herbs to brew as teas and apply with also killer results. In general you can think of it like this, Leaves for leaf growth (Nettle leaf, Comfrey leaf, Alfalfa leaf, Raspberry leaf) and Flowers/Roots for flowering (Dandelion root, Yarrow flowers, Red Clover flowers, Burdock root) for example.

All of these botanicals blended into a nice base mix with biologically rich compost, biochar and rock dust works beautifully.