There is a growing interest in converting organic wastes to charcoal for use as a sustainable soil amendment with a potential to improve soil productivity and sequester C. Three consecutive greenhouse experiments were conducted to investigate the effects of charcoals with different ash and volatile matter (VM) contents on soil properties and maize (Zea mays) growth and to evaluate the effect of time on charcoal performance. Five charcoal (high VM corncob, low VM corncob, kiawe, binchotan and a gasification charcoal of Leucaena leucocephala) amendments applied at a 2.5% (wt/wt) rate were compared with a zero-charcoal control with and without fertilization. Only the gasification charcoal significantly increased maize growth without fertilization. The low VM corncob charcoal with fertilization significantly increased maize growth by 164% compared with the fertilized control in the first planting cycle. Maize growth in the high VM corncob charcoal supplemented with fertilizer treatment was significantly lower than that of the fertilizer alone treatment in the first planting cycle. The negative effect of the high VM charcoal on the fertilizer was due to bioavailable carbon in the charcoal, which increased soil microbial activity and could have caused N immobilization. Both the beneficial and detrimental effects of charcoal did not persist beyond the first planting cycle suggesting charcoal impacts are temporary. While charcoal ash and VM content appear to be important parameters for predicting charcoal behavior in the short-term, more research is need to examine a broader spectrum of feedstocks exposed to varying thermal treatments.