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Amaranthus palmeri

Palmer's amaranth

Amaranthaceae

Desert Southwest US and northern Mexico

Drought Tolerant

Native to North America

SunFull Sun

WaterLow · drought-tolerant

Overview

Amaranthus palmeri is an erect, fast-growing summer annual reaching 3-8 feet (0.9-2.4 m) tall, occasionally taller in rich soil, with a stout, smooth, often reddish central stem. The plant branches into a broad, candelabra-like form. Alternate leaves are oval to diamond-shaped, 1-3 inches (2.5-7.5 cm) long on long stalks, and often carry a small notch and a tiny bristle at the tip. The species is dioecious, with male and female flowers on separate plants in dense, slender terminal spikes 6-18 inches (15-45 cm) long. Female spikes bear sharp, rigid bracts that make them prickly to handle. A single female plant can produce 200,000 to 600,000 small seeds in one season. Flowering runs from June to October. It grows on disturbed ground, croplands, riverbanks, and roadsides, tolerating heat and drought through a deep taproot and water-efficient C4 photosynthesis. The species has evolved resistance to several herbicides and is a major weed of cotton and soybean fields. The young leaves and seeds are edible and were eaten by Indigenous peoples of the Southwest.

Native Range

Amaranthus palmeri is native to the desert Southwest of the United States and northern Mexico, centered on the lower Colorado River basin. It has spread widely across North America as an agricultural weed and grows on cultivated fields, disturbed soil, floodplains, and roadsides.

Suggested Uses

Grown occasionally as a warm-season leaf and grain crop, where young leaves and seeds are harvested for food. In the wild it serves mainly as a seed source for birds and small mammals. It is more often managed as a weed than planted, given its rapid spread and herbicide resistance.

How to Identify

Identify by the tall smooth stems, long-stalked diamond-shaped leaves, and the slender flower spikes that can reach 18 inches (45 cm). Female spikes are sharply prickly to the touch, while male spikes are softer. Separate plants bear only male or only female flowers, unlike many similar pigweeds.

Appearance

Size & Dimensions

Height3' - 8'

Width/Spread1' - 3'

Colors

Flower Colors

green

Foliage Colors

green

Fall Foliage Colors

no change

Bloom Information

Bloom Period

~18 weeks

Summer Fall

Greenish flowers crowd dense terminal spikes from June to October, peaking in late summer. The wind-pollinated flowers have no petals and little visual presence. Female plants set enormous quantities of seed that ripen from late summer into fall.

Detailed Descriptions

Foliage Description

Green, stems often reddish

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 Range5.5 - 7.5(Neutral)

357912

Soil Types

loam sand clay silt

Drainageaverage

Water & Climate

Water Needs

Low

Drought Tolerance

Drought tolerant when established

Care & Maintenance

Care Guide

Amaranthus palmeri grows readily in full sun on warm, fertile, disturbed soils and is rarely planted on purpose. It tolerates heat, drought, and a wide pH from 5.5 to 7.5 through a deep taproot and efficient warm-season photosynthesis. Seeds germinate over a long season once soils warm, and plants grow several inches a week in summer. The species is dioecious, so seed forms only where male and female plants grow together. It is regulated as a noxious weed in several US states because of its herbicide resistance and heavy seed production. Removal before the female plants set seed is the main means of control.

Pruning

Pruning is not a normal practice for this weedy annual. Cutting or pulling plants before the female spikes mature prevents the large seed set. Severed stems can resprout from the base if soil moisture is high.