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Plant type

Perennial herb


4 - 7 ft Tall
1 ft Wide




Winter Semi-deciduous



Flowering season

Summer, Fall

Common uses


Ambrosia psilostachya is a species of ragweed known by the common names Cuman ragweed, perennial ragweed, and western ragweed. It is native to most of North America including all of southern Canada, nearly all of the continental United States, and the northern half of Mexico. It is a common plant in many habitat types, including disturbed areas such as roadsides. It can be found in parts of Eurasia as an introduced species. This is an erect perennial herb growing a slender, branching, straw-colored stem to a maximum height near two meters, but more often remaining under one meter tall. Leaves are up to 12 centimeters long and vary in shape from lance-shaped to nearly oval, and they are divided into many narrow, pointed lobes. The stem and leaves are hairy. The top of the stem is occupied by an flower cluster which is usually a spike. The species is monoecious, and the flower cluster is composed of staminate (male) flower heads with the pistillate heads located below and in the axils of leaves. The pistillate heads yield fruits which are achenes located within oval-shaped greenish-brown burs about half a centimeter long. The burs are hairy and sometimes spiny. The plant reproduces by seed and by sprouting up from a creeping rhizome-like root system. This plant had a number of medicinal uses among several different Native American groups.


Full Sun


Low, Moderate, High

Summer irrigation

Max 1x / month once established

Cold tolerance

Tolerates cold to 15° F

Soil drainage


Soil description

Soil PH: 5.2 - 8.2

Ambrosia psilostachya can do well in a variety of conditions, so the soil type of your garden will best inform which other plants to choose. Consider using other natives that do well in sunny, sandy sites, such as Nuttall's scrub oak (Quercus dumosa), Desertbells (Phacelia campanularia), or the Bristly Matilija poppy (Romneya trichocalyx).


Phacelia campanularia

Nuttall's Scrub Oak

Quercus dumosa

Bristly Matilija Poppy

Romneya trichocalyx


Butterflies and moths supported

2 confirmed and 20 likely

Confirmed Likely

Garden Webworm Moth

Achyra rantalis

Ambrosia Plume Moth

Adaina ambrosiae

Ancylosis morrisonella

Oso Flaco Flightless Moth

Areniscythris brachypteris

Site type

Commonly occurs throughout California on roadsides, disturbed areas, and dry fields.

Plant communities

Weed (disturbed places), Wetland-Riparian,