How often malted barley should be used:
every 7 - 10 days especially during the flower cycle. The increase in the resin set more than justifies whatever monies or effort you put out.
But more importantly is the huge increase in the overall health of your plants. There's a lot of reasons but one has to consider the chitinase from the malted barley grain with the internal and added levels of salicylic acid from regular applications of
aloe vera extract that gives you the increased SAR dynamic via
chitinase-salicylic acid pathways and
ethylene-salicylic acid pathways...