A few growers place charcoal in the bottom of containers to absorb excess salts and maintain sweet soil, if plants are grown more than a few months.
People who put charcoal at the bottom of their pots make sure to use special fertilizers 
( z1 ensure :ARG0 ( z2 person :ARG0-of ( z3 put :ARG1 ( z4 charcoal ) :ARG2 ( z5 bottom :part-of ( z6 pot :poss z2 ) ) ) ) :ARG1 ( z7 use :ARG0 z2 :ARG1 ( z8 fertilize :ARG1-of ( z9 special ) ) ) )