Marrubium rotundifolium Silver Edged Horehound is one our very best xeric groundcovers for poor soil areas with hot, sunny growing conditions. The soft felted leaves are green with a bright silver underside that curls up to give the leaves a silver edge. Drought resistant/drought tolerant plant (xeric). Zone 4, Zone 5, Zone 6, Zone 7, Zone 8, Zone 9