Aeration stones promote healthy root growth by creating air pockets in the soil and absorbing excess water in the basin of your planter. These porous clay stones are a natural, efficient and invaluable material to set your plant up for success. * Small stones are ideal for 4"- 8" planters, and their increased density allows for extra water absorption insuring younger plant don't dry out. * Medium stones are versatile and can be used in any planter.