Western ragweed
Ambrosia psilostachya
Care
full sun
low
Fast, Medium, Slow; Adaptable.
4–7ft tall , 1–1ft wide
Jun-Nov
Deciduous
Friendly
Grasslands and open areas from northeastern California south to San Diego County, below 5000 ft elevation, extending east to the Great Plains.
Care Guide
Planting
Plant western ragweed in full sun with well-draining soil - it's highly adaptable to fast, medium, or slow drainage, so soil type is flexible. This native perennial spreads via both seeds and underground rhizomes, so give it space to expand; it typically grows 4–7 feet tall but can be kept under one meter with management. Plant in spring or fall to establish before the growing season.
After Planting
Water weekly during your first summer, then cut back to once a month or less once established - this plant thrives on low water and needs minimal irrigation. The biggest mistake is overwatering; western ragweed is drought-tolerant and will rot in soggy soil. The plant is deciduous and will die back in winter; you can cut it back after frost. Year one focus is root establishment; after that, expect vigorous growth and flowers from June through November with almost no maintenance needed.
Wildlife Supported
Birds
Important winter seed source in California; visits ragweed for nutrition during lean months
Regularly forages on ragweed seeds; year-round resident in California
Irruptive winter visitor; opportunistically feeds on small seeds including ragweed
Winter visitor; supplemental seed source during invasion years
Ground forager; feeds on fallen ragweed seeds in southwestern California
Insects
Adult butterfly visitor to ragweed flowers; California desert and foothill populations
Migratory butterfly; multiple generations utilize ragweed nectar
Spring-active mining bee; provisions nests with ragweed pollen
Halictid bee specialist on ragweed pollen; multiple California populations