Production
Prepare 1kg fresh, thick-featured herbs in 10litre of water, best in wooden barrels, stoneware or polyethylene. You can also buy dried herbs or dry mixtures, then 150-200g/litre water are enough.
Place the barrel in a sunny and warm place, cover it with a grate. Now the sullage must ferment for 1-2 weeks, for the active ingredients like silicic acid can discharge.
The unavoidable smell nuisance can be kept in a limit by adding rock-flour with the daily agitation. The sullage is done, when it got a dark color and stopped foaming.

Exercise
The sullage will be sieved and with water 1:10 attenuated, then you can spray the plants preventive upside and underneath their leaves or you can fertilize them. Apply sullages best in the evening, because leave-burns could happen. The ingredients for preparing the sullage or adequate plant extracts are listed as plant-strengthener by the "Federal Office of Consumer Protection and Food Safety" and offered by various companies in stores:

• Weblinks
  www.bvl.bund.de - A list of plant-strengthener (PDF)