Photo: Le.Loup.GrisCC BY-SA 3.0via Wikimedia Commonsresized / cropped
Giant ragweed Plant Care
Ambrosia trifida L.
Updated · Sources · How we source care data
This plant has large, three-lobed leaves that are deeply toothed and can grow up to 12 inches long. Originating from North America, Ambrosia trifida is sought after by plant collectors for its unique foliage and ability to attract pollinators like bees and butterflies.
Every 3–5 days
Full sun to partial shade
60–80°F
40–60%
At a glance
How do you care for Giant ragweed?
Water Giant ragweed every 3–5 days, letting the top layer of soil dry out between waterings, and give it full sun to partial shade. It prefers temperatures of 60–80°F (16–27°C) and 40–60% humidity. Fertilize it every 6 months during the growing season. It is reported as toxic to pets, so keep it out of reach of pets.
Where Is the Giant ragweed Native To?
What Is the Giant ragweed?
Giant ragweed (Ambrosia trifida) belongs to the Asteraceae family within the Ambrosia genus. Giant ragweed is native to North America. Giant ragweed is also known as Great ragweed, Horseweed, Bitterweed.
Giant ragweed displays a spreading herbaceous perennial growth habit, reaching up to 2 ft tall with a spread of approximately 3 ft. Giant ragweed produces small green flowers in inconspicuous clusters.
Leaf size: approximately 4 inches.
How Often Should You Water a Giant ragweed?
Ambrosia trifida requires watering every 3–5 days. Allow the top layer of soil to dry between waterings to prevent root rot. Reduce watering frequency during winter when growth slows.
Watering Frequency
Every 3–5 days
Let soil partially dry between waterings
What Light Does the Giant ragweed Need?
Giant ragweed thrives in full sun to partial shade.
Light Requirement
Full sun to partial shade
What Temperature and Humidity Does the Giant ragweed Prefer?
Ambrosia trifida grows best at temperatures of 60–80°F. Giant ragweed prefers humidity levels of 40–60%.
Temperature
60–80°F
Humidity
40–60%
What Soil Mix Works Best for a Giant ragweed?
Well-draining sandy soil mix with added organic matter. Good drainage is essential for Giant ragweed to prevent waterlogging, which leads to root rot and fungal issues.
How Often Should You Fertilize a Giant ragweed?
Feed Giant ragweed every 6 months during the growing season (spring and summer) with a balanced fertilizer diluted to the strength on the label.
Pause feeding in autumn and winter, when growth slows, and never fertilize dry soil — water first.
Fertilizing
Every 6 months
During the growing season
The PlantoScan app can remind you when to water and when to fertilize each plant.
How Do You Repot a Giant ragweed?
Repot every 1-2 years in early spring. Choose a pot one size larger than the current container, and ensure it has drainage holes to allow excess water to escape.
How Do You Propagate a Giant ragweed?
Giant ragweed can be propagated through seeds. Similar propagation techniques also apply to common ragweed plant care, which shares the same genus.
Is the Giant ragweed Toxic to Pets and Children?
Toxic (caution)
Reported as toxic in our plant data. Not verified by the ASPCA.
Toxic to humans and pets if ingested
This is a general caution, not veterinary or medical advice. If your pet ate a plant, contact your vet or animal poison control.
See all plants toxic to cats and plants toxic to dogs.
What Pests and Diseases Affect the Giant ragweed?
Giant ragweed is susceptible to aphids, spider mites, whiteflies. Inspect the foliage regularly, especially along leaf undersides and stems. Treat infestations promptly with insecticidal soap or neem oil to prevent spread.
Yellow leaves, brown tips or drooping? See common plant problems and how to fix them.
What USDA Hardiness Zone Does the Giant ragweed Need?
Giant ragweed grows outdoors in USDA Zone 3a – 10b. It survives winters down to planting zone 3a. Giant ragweed is native to North America.
Hardiness Zone
Zone 3a – 10b
Keep exploring plants
Giant ragweed is one of many species covered in the complete plant care and identification guide, which groups plants by genus, attribute, and popularity.
It belongs to the Ambrosia genus — compare its care with other Ambrosia species on PlantoScan.
Ambrosia is part of the Asteraceae plant family — browse all Asteraceae genera and species.
Giant ragweed thrives in bright light and direct sun — see other bright-light plants.
More Ambrosia Species
Other Ambrosia species in PlantoScan's care catalogue share similar watering, light, and soil preferences:
Sources
- Scientific name & taxonomy: Ambrosia trifida L., family Asteraceae (first published in Sp. Pl. : 987 (1753)) — World Flora Online record, IPNI name record.
- Pet toxicity: Giant ragweed is reported as toxic to pets in our plant data (not verified by the ASPCA), so treat it with caution. Checked against the ASPCA plant list; any other toxicity note on this page comes from PlantoScan's plant database.
- Photo: Le.Loup.Gris, CC BY-SA 3.0, Wikimedia Commons — original.
- Hardiness zone: USDA Zone 3a – 10b, estimated from the plant's typical growing conditions.
- Care values(watering, light, temperature, humidity, soil, fertilizing): PlantoScan's plant database, filtered by automatic plausibility checks — values that fail them are hidden. How we source and check plant data.
Spotted a mistake? Email info@upvision.media with the page link — we check and correct reported errors.
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