@dobber
The owner of my house prior to me loved them some lava rock rather than mulch in the planters around the house. Rock, for some reason, loves it some crab grass(only place I have much of it at all is in these planters). Can I torch that crap with something that will kill it without killing my moss rose, cone flower, rhododendron, hybiscus, knockout roses, mums, astors, silvia, rubeckia, gailardia, flocks, etc or do I need to actually pull weeds like every other night for the rest of my life(or at least until I get the time to replace the rock with something else)?