Island alum root

Sun

Partial shade; tolerates full sun near the coast if the soil does not dry out completely. Protect from hot afternoon sun inland.

Water

Water regularly during establishment. Established plants tolerate some summer dryness in shade, but occasional deep watering keeps the foliage fuller; avoid constantly wet soil.

Soil

Well-drained soil, preferably with some leaf mould or compost. Tolerates clay where drainage is good, but dislikes waterlogged winter soil.

Height

1-2 ft (0.3-0.6 m) in leaf; 3-4 ft (0.9-1.2 m) in flower

Spread

2-3 ft (0.6-0.9 m)

Flowers

Spring to early summer; small creamy-white to pale pink flowers on tall, branching stems.

Foliage

Broad, rounded, shallowly lobed green leaves form a substantial basal clump. Foliage is generally evergreen in mild climates but may look worn after frost or drought.

Growth

Moderate

Care needed

Low

• Pollinators
• Drought tolerant
• Heat tolerant
• Low allergen

Northern hemisphere months. In Australia, shift them by six.

Difficulty

Moderate

Toughness

Fairly tough

Pick your zone, country, light and whether you have pets.

1. Planting day

   1 ft (0.3 m)

2. After 1 year

   1.1 ft (0.35 m)

3. After 2 years

   1.3 ft (0.4 m)

4. After 3 years

   1.5 ft (0.45 m)

   full size

About 3 years to full size.

From a typical nursery size, at an average rate for this kind of plant. A rule of thumb, not a forecast.

Cats and dogs

Safe

Native to

the US

Growth rate

Moderate

• Plant with the crown at soil level, not buried beneath soil or mulch.
• Water deeply during the first growing season, allowing the surface soil to dry slightly between waterings.
• Apply a thin layer of leaf mould or compost in spring; routine heavy feeding is unnecessary.
• Mulch around the clump to conserve moisture, keeping the crown clear.
• Divide ageing clumps in spring if the centre becomes woody or growth weakens.

Pruning. Remove dead or damaged leaves in late winter or early spring without cutting into the crown. Cut spent flower stems back to their base after flowering.

Early spring

Remove winter-damaged leaves and check that soil or mulch has not covered the crown.

Spring

Plant or divide clumps, water them in well, and add a light compost dressing.

Late spring

Enjoy the flower sprays; leave some standing while insects are visiting.

Summer

Water established plants occasionally during prolonged dry spells and remove finished flower stems.

Autumn

Plant in mild climates while the soil is warm, leaving enough time for roots to establish before winter.

Winter

Check drainage and clear wet debris from around the crown.

• Plant in loose groups beneath open-canopied trees for a broad-leaved, evergreen ground layer.
• Edge shaded paths with clumps, allowing room for the leaves to spread without covering the walkway.
• Combine with ferns and fine-leaved grasses to contrast bold leaves with softer textures.
• Use in coastal California native planting, where the pale flower sprays lighten shaded areas.

Garden styles it suits: California native, Woodland, Coastal, Wildlife garden, Low-maintenance and Mediterranean.

Plant it with: Western sword fern, Douglas iris, California fescue, Hummingbird sage and Western columbine.

Wildlife: The flowers provide nectar and pollen for visiting insects, including bees. Hummingbirds may also visit within their range.

• Crown or root rot in wet soil: improve drainage, reduce watering and keep mulch away from the crown.
• Leaf scorch in hot sun or dry wind: provide afternoon shade and water deeply during extended dry weather.
• Vine weevil larvae, especially in pots: inspect declining plants for root damage and use an appropriate biological control where available.
• Slugs and snails on young foliage: remove hiding places near the crown and use traps or locally approved controls if damage is significant.

Not known to be toxic to people, cats, dogs or horses; no poisonous parts are recognised. It is an ornamental plant, not a food crop.

• Small-flowered alumroot (Heuchera micrantha)

  Usually has smaller, more angular or sharply lobed leaves and a less substantial clump; island alum root has notably broad, rounded foliage.

• Coral bells (Heuchera sanguinea)

  Usually has smaller leaves and conspicuous red or deep pink flowers, rather than the large leafy clump and pale flower sprays of island alum root.

Heuchera honours the German physician and botanist Johann Heinrich von Heucher, while maxima means largest, referring to its unusually large size among heucheras.

Propagation. Divide healthy clumps in spring, retaining roots and growing points on each section. Sow seed in a free-draining seed compost with only a very light covering; seedlings from plants growing near other heucheras may be hybrids.

Accepted botanical name

Heuchera maxima

In the US and Canada

Native in the lower 48 states.

Native range

California.

Sources: GBIF (CC BY 4.0), USDA PLANTS and Trefle (CC BY 4.0). The care and design notes are LandscapeGPT's own.