Heuchera maxima is endemic to the Channel Islands of California, where it colonizes shaded canyon walls and rocky outcrops on Santa Cruz, Santa Rosa, and Anacapa islands. It is significantly larger than most heucheras, producing bold lobed foliage and tall wands of small white to pinkish flowers that attract hummingbirds. In coastal and mild-climate gardens it functions as an evergreen groundcover for dry shade, a niche few perennials fill reliably.
Established plants tolerate summer drought, which is unusual among shade perennials. Plant in sharply drained soil with good air circulation; wet, heavy soil in winter is the primary driver of crown rot and Phytophthora loss. A gritty or rocky planting medium closely mimics the native cliff habitat and improves long-term vigor. Divide clumps every four to five years when the crown becomes woody and heaves above the soil surface.
Like other alum roots, the roots and leaves are high in tannins, which gives the genus its common name and accounts for its documented astringent properties. Indigenous peoples of coastal California used related Heuchera species as astringents for wounds, gastrointestinal complaints, and mouth inflammations.
Crown Rot
Lower leaves yellow and wilt; the base of the rosette turns brown and soft, sometimes with white fungal threads at the soil line. Plants collapse in wet conditions.
Remove and destroy affected plants. Improve drainage and avoid overhead watering. Do not mulch directly against the crown. Space plants for airflow and avoid replanting in the same wet spot.
Powdery mildew
White or grey powdery coating on leaves — usually starting on older growth in humid conditions or when nights cool.
Improve air circulation by thinning plants. Apply neem oil or potassium bicarbonate spray at first sign. Avoid overhead watering.
Phytophthora Root Rot
Wilting despite moist soil, yellowing leaves, stunted growth, and dark, decayed roots and crown tissue. Vines may collapse during hot weather.
Plant in well-draining soil and avoid waterlogging. Remove and destroy affected vines. Improve drainage with raised beds or amended soil and avoid overwatering.