Isocoma spp.

Asteraceae

Southwestern United States and northern Mexico

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant Fragrant (light)

Native to North America

SunFull Sun

WaterVery Low · drought-tolerant

HardinessZones 7–10

Overview

Isocoma spp. is a genus of about sixteen species of bushy, resinous shrubs and subshrubs in the daisy family, Asteraceae, native to the southwestern United States and Mexico. Plants form rounded, much-branched bushes 1 to 4 feet (0.3 to 1.2 m) tall, with narrow, often sticky or gland-dotted leaves and a strong scent. Unlike many daisies, the small yellow flower heads have no spreading ray florets and are made up only of tubular disc florets, gathered into dense flat-topped clusters at the branch tips. Flowering comes mainly in late summer and autumn, when the bushes turn yellow with bloom. The genus grows across arid and semi-arid country, on alkaline flats, desert grassland, roadsides, and rangeland, often on poor or saline soils. Several species, including I. pluriflora (rayless goldenrod), contain the toxin tremetol; livestock that eat the plant can be poisoned, and the toxin can pass into milk and cause illness in people who drink it. The resinous foliage and late bloom suit dry gardens, though the plants can look weedy and spread on disturbed ground.

Native Range

Isocoma spp. is native to the southwestern United States and northern Mexico. The plants grow in arid and semi-arid grassland, desert scrub, alkaline flats, and disturbed ground.

Suggested Uses

Isocoma spp. is used in dry, desert, and native gardens and in restoration of arid disturbed sites in its native range. The resinous foliage and late-season yellow bloom support pollinators when little else flowers. Because of the toxic foliage, the genus is planted in ornamental settings rather than on grazing land.

How to Identify

Plants are low, rounded, much-branched shrubs 1 to 4 feet (0.3 to 1.2 m) tall with narrow, resinous, gland-dotted leaves that are often sticky and aromatic. The small yellow flower heads lack spreading ray petals and consist only of tubular disc florets, packed into dense flat-topped clusters in late summer and autumn. The rayless yellow heads on a resinous desert shrub separate Isocoma spp. from true goldenrods (Solidago spp.) and rabbitbrush (Ericameria spp.).

Appearance

Size & Dimensions

Height1' - 4'

Width/Spread1' - 4'

Colors

Flower Colors

Foliage Colors

Fall Foliage Colors

Bloom Information

Bloom Period

~8 weeks

Summer Fall

Flowering occurs from late summer into autumn, roughly August to October. The heads are yellow and rayless, made only of tubular florets, and are clustered at the branch tips. Bees, wasps, and butterflies visit the late-season flowers for nectar.

Detailed Descriptions

Foliage Description

green to grey-green

Growing Conditions

Sun Requirements

SunFull Sun

Requires 6-12 hours of direct sunlight daily

• Full Sun: 6+ hours of direct sunlight

• Partial Shade: 3-6 hours of direct sunlight

• Full Shade: Less than 3 hours of direct sunlight

Soil Requirements

pH Range6.5 - 8.5(Alkaline)

357912

Soil Types

sand loam rocky clay

Drainagewell drained

Water & Climate

Water Needs

Very Low

Frost Tolerance

hardy

Time to Maturity

2-3 years

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Isocoma spp. grows in full sun in dry, well-drained, often alkaline or saline soils, and tolerates poor, rocky, and disturbed ground. The genus is adapted to heat and drought and is hardy in roughly USDA zones 7 to 10, depending on species. Plants need little or no supplementary water once established and decline in rich, moist, or poorly drained soil. Several species are toxic to grazing animals through the compound tremetol, so they are unwelcome on grazing land. Propagation is by seed sown in autumn or spring, or by cuttings of semi-ripe wood.

Pruning

A light trim in late winter or early spring keeps the bushes compact and removes old flowering stems. Cutting back hard into bare wood is left undone, as the plants resprout slowly from old stems. Spent flower clusters can be sheared after bloom.

⚠️ Toxicity Warning

Toxic to pets and humans

Shrubs

Isocoma spp.

Asteraceae

Southwestern United States and northern Mexico

Attracts Pollinators Attracts Butterflies Deer Resistant Drought Tolerant Fragrant (light)

Native to North America

SunFull Sun

WaterVery Low · drought-tolerant

HardinessZones 7–10

Overview

Native Range

Isocoma spp. is native to the southwestern United States and northern Mexico. The plants grow in arid and semi-arid grassland, desert scrub, alkaline flats, and disturbed ground.