After a number of experiments, I’ve come up with an almost perfect way to breakdown charcoal – just add water. In my quest to make terra preta, I have tried to breakup charcoal to a usable size by using blenders and bricks, but my latest test proved the best. If you use charcoal briquettes and submerge them in water, the glue which hold them together breaks down and with a little gentle coaxing and kneading they break down into a black gruel. If you then let it dry out about 90% you can then easily break it up with your hands. You then have a great soil amendment.
At this point, spread it around your garden and try to work it into the soil.