Silvery beachweed
Ambrosia chamissonis
Care
full sun
low
Fast; Prefers beach sand.
4–4ft tall , 7–7ft wide
Jun-Nov
Evergreen
Resistant
Friendly
Coastal beaches and dunes from Humboldt County to San Diego County, below 500 ft elevation in sandy coastal habitats.
Care Guide
Planting
Plant silvery beachweed in full sun with fast-draining soil - ideally sandy soil like what you'd find on a beach. Space plants several feet apart since they sprawl widely (up to 10 feet across at maturity). Plant in spring or fall when soil moisture is naturally higher to help establishment. This plant tolerates poor, sandy soils where other plants struggle, so don't amend with rich compost.
After Planting
Water weekly for the first summer to establish, then transition to low water once the plant is mature (by year two). Silvery beachweed is evergreen and will grow year-round in the Bay Area with minimal intervention - no pruning needed unless you want to contain its sprawling growth. The biggest mistake is overwatering; this coastal native prefers dry conditions and will decline in wet soil, so err on the side of dry once established.
Endangered & Threatened Species Supported
California Endangered Species Act listed
Wildlife Supported
Mammals
primary seed harvest and caching for winter food stores
Insects
larvae feed on plant foliage during spring and early summer generations
larvae induce galls on flowers and developing seeds; multiple generations
larvae develop within seed pods and developing seeds
overwinter larvae feed on foliage and buds in coastal dune habitat
parasitic plant that weakens Ambrosia chamissonis in coastal salt marsh ecotone
nest in sandy areas around Ambrosia chamissonis in beach and dune habitat