Redroot pigweed (Amaranthus retroflexus
) is a spring and summer annual broadleaf weed which is commonly found throughout the United States. Seedlings emerge over an extended period, with major flushes in late spring or early summer. Redroot pigweed flowers bloom from July to September.
The reddish or pinkish taproot is shallow compared with the size of the weed. The erect stems are green to slightly reddish and have many branches. Lower portions of the stem are thick and relatively smooth; upper portions are very hairy. It is drought tolerant and thrives in hot temperatures. There is also evidence that it releases chemicals that interfere with the growth of nearby plants.
Redroot pigweed is a nitrate accumulating plant, having the potential to cause nitrate poisoning
in horses, under certain environmental conditions. Nitrate levels are at their highest just prior to flowering, following droughts, and if treated with herbicides.