Our planter boxes and raised garden beds have built in drainage, and excellent airflow! Therefore, adding materials such as river rocks or other stones for drainage is not needed, and actually discouraged due to the unnecessary weight of the rocks. If you wanted to add materials to reduce the amount of soil needed, you can simply add leaves, sticks, or compostable materials such as cardboard, to the bottom of the planter box or raised garden bed. You can even use the cardboard packaging from your Cedar Planters order!