I am very familiar with Sam Biser, Dr. Schulz, and I would add these:
Hulda Reghr Clarke
Hanna Kroeger
Johanna Budwig
I have made tinctures based on above teachings, and what is usually left unsaid is: Prepare your tinctures during a NEW MOON; Harvest your tinctures on the FULL MOON. In the interim, place the dark glass container containing your receipe in a window where the moonlight can bathe it.
Shake it thoroughly at LEAST twice a day. The longer they sit, the stronger they become!