Plant Problem Diagnostic
Redroot Pigweed (Redroot Amaranth) Identification and Control
The short answer
Redroot pigweed (Amaranthus retroflexus), also called redroot amaranth, is a summer annual named for its distinctive pinkish-to-red taproot. It grows commonly around 3 feet, occasionally up to nearly 10, on coarse stems that are hairy toward the top, with alternate, dull green, egg- to diamond-shaped leaves and small green flowers packed into dense, prickly terminal spikes.
It matters because it seeds so heavily: a single plant can produce an average of 13,000 to 35,000 seeds, which germinate over several years, so early removal before seed set is the whole ballgame. Because seedlings germinate in only the top inch of soil, hand-pulling works well (and is easier after rain or watering), and cutting larger plants at the base before seeds develop prevents future infestation.
Its constant companion and lookalike is lambsquarters: pigweed has the red taproot, coarse hairy stems, and prickly seed spikes, while lambsquarters wears a white mealy coating and has no red root.
How to identify it
Check the root and the stem. Pigweed is named for its pinkish-to-red taproot, and its coarse stem is pale green to reddish, usually nearly red at the base, with upper stems ranging from hairy to densely hairy. The leaves are alternate, dull green, and egg- to diamond-shaped lower down grading to lance-shaped above, with the seedling's first true leaf notched at the tip and often reddish beneath.
The flowers are the giveaway later in the season: small and green, packed into dense, bristly, prickly spikes at the stem tips and leaf axils, blooming from summer into fall. The plant stands erect, commonly around 3 feet but occasionally much taller in rich soil.
Why the seed bank is the real problem
One plant is a seed factory. Penn State reports a single pigweed can produce an average of 13,000 to 35,000 seeds, and those seeds germinate over several years, so a plant that seeds this year keeps you weeding for many more. The math is sobering: it can take three years to reduce the soil seed bank by half, and up to 20 years to reach 99 percent.
That is why the entire strategy points at stopping seed set. Every plant you remove before it flowers is thousands of future seedlings that never happen, and every plant you let seed resets the clock.
Control
Pull early and shallow. Because pigweed germinates in the top inch of soil, seedlings hand-pull easily, and doing it after rain or watering makes the job cleaner. For larger plants that are hard to pull, cut them off at the base of the stem before seeds develop, which prevents future infestation just as well as pulling. A mulch layer shades out emerging seedlings.
If you consider a herbicide to manage the seed bank, note Extension warns that pigweeds have evolved resistance to a range of herbicides, including glyphosate, so chemical control is not a shortcut; follow the product label and county Extension guidance, as no rates are given here. Distinguish it from lambsquarters (white mealy coating, no red root) so you know both are prolific seeders worth removing young.
Sources
Reviewed 2026-07-18. We cite university Extension, government, and established horticultural sources — and never invent pesticide rates or dangerous treatments.
- Penn State Extension - Managing Pigweed in the Home Garden — Pigweeds are annual Amaranthus weeds 3 to 6 feet tall with alternate oval to diamond-shaped leaves tapering to a point and smooth or hairy stems; one plant can produce an average of 13,000 to 35,000 seeds that germinate over several years, taking three years to reduce the soil seedbank by 50 percent and up to 20 years to reach 99 percent; because germination occurs in the top 1 inch of soil, hand-pulling seedlings (easier after rain or watering) and cutting larger plants at the base before seeds develop are effective, mulching shades out seedlings, and pigweeds have evolved resistance to herbicides including glyphosate.
- UC IPM - Redroot Pigweed (Weed Gallery) — Redroot pigweed (Amaranthus retroflexus) is a summer annual named for its pinkish to red taproot, growing to about 3 ft and up to nearly 10 ft tall with coarse stems and upper stems ranging from hairy to densely hairy; cotyledons are long narrow lance-shaped with reddish undersides, the first leaf is egg-shaped with a notched tip, and true leaves are broader with notched tips and often reddish lower surfaces and veins; it flowers June through November and produces glossy dark reddish-brown to black seeds roughly 1-1.5 mm in diameter.