Island Alum Root (Heuchera maxima) is a species of flowering plant in the saxifrage family. It is endemic to three of the eight Channel Islands of California, where it grows on cliffs. It is rare in the wild due to its limited distribution. However, it is also cultivated as an attractive garden plant, valued for both its foliage and flowers.
Island Alum Root is a two-foot-tall perennial growing a broad patch of large, rounded, multi-lobed green leaves with long leaf stalks and a fringe of hairs along the edges with 3-foot-tall spikes of small pinkish flowers emerging from February to April. Each flower is rounded with fleshy white or pink lobes and tiny petals curling away from the center. The protruding stamens are tipped with large anthers.
This alum root likes part to full shade. A good edging plant in a shady border. The large 3″to 5″ dark green leaves and spikes of small pinkish flowers make it appear very delicate but it’s surprisingly drought tolerant. These plants are very lush near the coast as long as salt spray doesn’t reach them. It is the preferred groundcover under evergreen oaks in California. Beautiful in massed plantings under evergreen oaks. Plant about 2 feet apart with shredded redwood bark or shredded cedar bark as a 2″-4″ mulch, unless there are sufficient oak leaves to use as mulch. This Heuchera species is hardy to about 12 degrees F.
Island Alum Root reproduces vegetatively as a rhizome.
Heuchera maxima tolerates alkaline soil and clay.
It performs best in coastal gardens where it can take full sun to part shade. In inland gardens it may require full shade and additional water. It looks good in woodland gardens.