Is giant ragweed the same as goldenrod?

No, they are different plants, though they often bloom at the same time.

How do I stop it from spreading?

Pull the plants before they set seed in late summer.

Plant guide

Giant ragweed.

Ambrosia trifida

Pronounced am-BRO-zee-uh TRY-fih-duh

Also known as Blood Ragweed, Buffalo-weed, Giant Ragweed, Great Ragweed, Great Ragweed, Buffalo-weed, Horseweed, Perennial Ragweed, Tall Ragweed

Giant ragweed is a fast growing annual plant often found in disturbed soils and along roadsides. It is well known for producing large amounts of windborne pollen that can trigger allergies. You will typically see it reaching impressive heights by late summer.

Another photo of Giant ragweed — Photo by Roz Hunter (CC BY) via iNaturalist

At a glance

Care level: Easy
Plant type: Annual herb
Light: Full sun
Indoor light: Direct sun
Water: Every 3 to 7 days
Mature size: 3 to 6 meters
Growth rate: Fast
Hardiness: USDA 2 to 11
Bloom time: Mid summer to early autumn

Care

This plant thrives in full sun and moist, fertile soil conditions. Watch for rapid expansion as it can easily outcompete other vegetation in the area. It does not require special care as it is considered a common weed.

Watering: Keep the soil consistently moist for optimal growth.
Feeding: Fertilizing is generally not necessary for this vigorous grower.
Pruning: Cut back or remove plants before they go to seed to manage spread.
Repotting: This plant is an annual and is not typically grown in containers.
Soil: Moist, nutrient rich soil
Soil pH: 6.0 to 7.5
Temperature: -30 to 35°C
Humidity: 40 to 70%
Drought tolerance: Moderate
Lifespan: Annual, completes its life cycle in one growing season.
Deer and rabbits: High

Safety

People: The plant is generally non-toxic if touched, but it is not meant for human consumption.
Children: Keep children away from the dense, tall stalks as they can be brittle and prone to snapping.
Contact allergens: The foliage can cause mild skin irritation in sensitive individuals upon direct contact.
Airborne allergens: This species is a primary source of highly allergenic windborne pollen that triggers severe hay fever.
Edibility: This plant is not considered edible and can cause digestive distress if consumed.

How to identify it

Large palmately lobed leaves
Opposite leaf arrangement on stem
Rough hairy stems and foliage
Tall stature reaching several meters
Small greenish flowers in spikes

Height: 1 to 4.5m
Spread: 0.6 to 1.5m
Leaves: green, deciduous
Flowers: green, yellow, 0.5 to 1cm
Fruit: brown, Autumn

Common problems

Powdery mildew — A fungal infection that leaves a white, dusty coating on the leaves during humid weather.

Growing it

Propagation: seed
When to plant: spring
Overwintering: The plant dies back completely after the first hard frost, leaving only seeds in the soil.
In containers: Not recommended for containers due to its massive size and aggressive root system.

Direct Sowing

Collect mature seeds in late autumn.
Scatter seeds on bare, moist soil in early spring.
Ensure the area receives full sun for best germination.

This plant is highly competitive and will likely crowd out smaller, slower growing native perennials.

Grows well with

Common Sunflower — They share similar moisture and light requirements in open fields.
Big Bluestem — This grass provides structural support in prairie restoration settings.

Similar species

Common Ragweed — It is a smaller relative with more finely divided, fern like foliage.

Science

Family: Asteraceae
Genus: Ambrosia
Order: Asterales
Class: Magnoliopsida
Native range: Most of North America, excluding the far north and extreme southwest.
Conservation: It is considered a common, often aggressive, native weed across much of its range.

It thrives in moist, nitrogen rich soils and is highly adapted to colonizing areas after flooding or soil disturbance.

Value to wildlife: seeds provide food for songbirds, larval host for certain moth species
Pollinators: bees, butterflies
Uses: wildlife habitat restoration, soil erosion control

Through the year

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Flowering

Fruiting

Foliage

Ecological indicators

Salinity: 2/9
Soil reaction: 6/9
Light: 7/9
Temperature: 5/9
Moisture: 6/9
Nutrients: 8/9

Taxonomy resolved against GBIF.

Questions people ask

Is giant ragweed the same as goldenrod?: No, they are different plants, though they often bloom at the same time.
How do I stop it from spreading?: Pull the plants before they set seed in late summer.

Where the name comes from

The genus name Ambrosia comes from the Greek word for food of the gods, while trifida describes the three lobed leaves.

Good to know

It is one of the fastest growing annual plants in North America.
The name trifida refers to the three distinct lobes found on its large leaves.
It often colonizes disturbed soil, such as roadsides and floodplains.

Also in

Deer-resistant plants

Is your giant ragweed looking unwell?

This page is a general guide. Pocket Botanist diagnoses problems from a photo of your actual plant, works out watering for your light and conditions, and reminds you when care is due.

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This guide was generated with AI and checked against GBIF taxonomy. It is general information, not horticultural or veterinary advice. Read about how we build these guides.