annualN. America Native

Palmer Amaranth

The Story

Plant Bio

Amaranthus palmeri, known as Palmer amaranth, is a fast-growing summer annual native to North America that reaches heights of six to ten feet. It develops a robust taproot and a highly branched, erect habit, thriving in full sun and adapting to almost any soil type.

This species is dioecious, meaning individual plants are exclusively male or female, with female plants producing dense, spiny seed spikes up to three feet long. It is distinguished from other pigweeds by its completely hairless stems and exceptionally long petioles that often exceed the length of the leaf blades.

Uses & Benefits:

This plant has no recognized ornamental value and is managed strictly as an agricultural and garden weed.

It serves as a subject for agricultural research regarding herbicide resistance and weed management strategies.

The abundant seeds are heavily consumed by ground-feeding birds and small mammals, and the flowers are visited by generalist insect pollinators.

Essentials

At a Glance

Plant Type

Annual

Height

118"

Width

24"

Light

Full Sun

Zones

4, 5, 6, 7, 8, 9, 10

Water

Low

Humidity

High to Low

Lifespan

Annual

Native To

North America

Toxicity

Toxic to livestock (nitrates/oxalates)

Bloom period

Summer – Fall

In flower about 6 months of the year

Planting

How to Grow

Sow seeds directly into disturbed, well-drained soil in a full-sun location after the danger of spring frost has passed.
Water lightly to establish the root system, though the plant quickly becomes extremely drought-tolerant.
Monitor the fast-growing stems, which can grow up to three inches per day, and ensure they do not crowd out desirable species.
Uproot and destroy the plants completely before the female spikes set seed to prevent aggressive colonization.

Pro Tip

To prevent this aggressive agricultural weed from self-seeding and spreading, manually pull or destroy the entire plant before the green flower spikes mature and release seed.

Keep It Thriving

Care Guide

Do

Identify and remove female plants early to prevent seed production.
Wear thick gardening gloves when handling mature female plants to avoid injury from the sharp, stiff floral bracts.
Dispose of pulled plants securely so that developing seeds do not contact the soil.

Don't

Do not allow livestock to graze on this plant, as it accumulates toxic levels of nitrates and oxalates.
Do not apply standard herbicides blindly, as many populations have developed widespread resistance to multiple chemical classes.
Do not plant this species near agricultural fields or home vegetable gardens where it can quickly become a destructive weed.

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Pest Check
Plant
Propagate
Prune

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

None recommended due to invasive weed status

Multiply

Propagation Methods

Good to Know

Common Questions

Palmer Amaranth questions

What zones can Palmer Amaranth grow in?

Palmer Amaranth is hardy in USDA Zones 4–10. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

Is Palmer Amaranth deer resistant?

Yes — Palmer Amaranth is rated deer-resistant. Deer typically pass it over, though extreme hunger can override any plant's defenses.

When does Palmer Amaranth bloom?

Palmer Amaranth typically blooms in summer through fall. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Palmer Amaranth need full sun?

Palmer Amaranth does best in full sun (6+ hours).

Is Palmer Amaranth drought tolerant?

Yes — once established (usually after the first full season), Palmer Amaranth handles dry spells with minimal watering. Water deeply its first year to build the root system that makes that possible.