Applying a layer of gravel in the bottom of a pot actually reduces drainage because the depth of soil decreases resulting in an increase in the relative water table. To improve plant growth in a container, always use a pot with drainage holes and fill the entire container with potting soil. If better drainage is still needed, mix additional perlite (heat expanded amorphous volcanic glass) into the potting soil when transplanting. For more information, visit the eXtension website: Indoor Plants.