Humic substances are used in agricultural production to induce better rooting capacity of plants and to increase crop biomass and yields. Compost produced from pineapple aerial biomass has been suggested as a source for the extraction of humic substances; however, no information is available regarding the effectiveness of humic substance extracts of this compost on crop production. The effectiveness of foliar applications of a humic substance extract from pineapple aerial biomass compost was evaluated in a greenhouse experiment. The experiment evaluated the effect of three foliar fertilizers, SH (humic substances), SH+NPK (humic substances with NPK) and NPK, on the root and aerial dry biomass of pak choy and lettuce. The results of this study clearly indicate that humic substance extract of pineapple aerial biomass compost was not effective in improving pak choy or lettuce production. The lack of effect of the extract was due possibly to very low or inexistent concentrations of humic substances in the extract, which might have resulted from the use of compost in which the appropriate humification processes had not occurred.