To use coal cake residue to plant flowers, you should first put it into the water to soak, it should be fully soaked, so that it can filter out the substances harmful to flowers. After that, it is crushed and dried, but be careful not to get powdered. Finally, when used, if the particles are large, you can pad in the bottom of the pot, if the particles are small, you can mix with the soil, fully mixed, you can plant flowers.