Lava rock is an excellent addition to your potted plants! Being porous allows water to filter through them, making them a breathable top dressing that won't trap moisture. Alternatively, create a layer of lava rock at the bottom of your planter for an additional bit of drainage. As a naturally occurring material, it won't leech any harmful substances into your soil. 

How much lava rock? This product is a 6 oz glass jar filled to the brim. You can bring this jar back for 15% off your refills! Discount potting material galore!