Hoffman Volcanic Lava Rock is a decorative soil cover that can be used indoors or outdoors. Product Details Genuine Red Colorado lava rock soil cover A great decorative moisture retainer for potted or bedded plants This product weighs 2 quarts Packaging appearance may vary Please note: lava rock attracts heat, direct contact can cause your plants to overheat Hoffman Volcanic Lava Rock is a decorative soil cover that can be used indoors or outdoors. It helps retain soil moisture and reduces compaction caused by frequent watering. Using lava rock screened (to remove large pieces and also dust) as mulch will not only keep weeds down due to the shading of the ground (most weed seeds need light to germinate) it also retains moisture in the shaded soil beneath it.