When does American cow-parsnip bloom?

American cow-parsnip typically flowers in June and July, producing large, flat-topped clusters of small white flowers held above coarse, broad leaves.

What pollinators visit American cow-parsnip?

Bees, beetles, and flies are frequent visitors to the wide, flat flower clusters, which offer easy access to nectar and pollen.

What growing conditions does American cow-parsnip prefer?

This forb does best in part sun with medium to consistently moist soil, and is often found along stream banks, wet meadows, and forest edges.

Is American cow-parsnip a shrub or a perennial forb?

It is a tall herbaceous forb, not a woody shrub, dying back to the ground each year and regrowing from its root system in spring.

Is American Cow-parsnip toxic to dogs?

Yes. American Cow-parsnip is listed as toxic to dogs by the ASPCA Animal Poison Control Center (aspca.org). If your pet has been exposed, call the ASPCA Animal Poison Control Center at (888) 426-4435.

Is American Cow-parsnip toxic to cats?

Yes. American Cow-parsnip is listed as toxic to cats by the ASPCA Animal Poison Control Center (aspca.org). If your cat has been exposed, call the ASPCA Animal Poison Control Center at (888) 426-4435.

Is American Cow-parsnip toxic to livestock?

American Cow-parsnip is listed as toxic to grazing livestock such as cattle, sheep, and goats (slight severity) by the USDA PLANTS Database. This is separate from pet (dog and cat) toxicity.

Is American Cow-parsnip HOA-friendly?

American Cow-parsnip takes more care to look intentional in a front yard. Consider it for backyard or mid-zone beds rather than the street edge.

American Cow-parsnip

Name: Pollinator Patch
Author: Pollinator Patch

Heracleum maximum

Last reviewed: October 2026

Heracleum maximum, or American cow-parsnip, produces broad flat clusters of small white flowers in June and July. It thrives in moist meadows, streambanks, and open woodland edges across much of the northern and eastern United States.

American Cow-parsnip (Heracleum maximum) — Photo: no rights reserved

American Cow-parsnip is toxic to dogs and cats.

Listed as toxic by the ASPCA Animal Poison Control Center (opens in new tab) (last reviewed 2026-05-21). If your pet has been exposed, call the ASPCA Animal Poison Control Center at (888) 426-4435 and your veterinarian's emergency line.

Pollinator Patch flags toxic plants so you can choose a pet-safe native alternative for your yard.

Native swaps for a yard with pets

American Cow-parsnip is listed as toxic to dogs by the ASPCA Animal Poison Control Center. These natives fill a similar role in a planting and are not on the ASPCA toxic plant list for dogs or cats. Each plant's page carries its dated record.

American Cow-parsnip is listed as toxic to grazing livestock such as cattle, sheep, and goats at a slight level by the USDA PLANTS Database (opens in new tab). This is a livestock indicator and is separate from pet toxicity.

Light

part sun

Water

medium

Size

36"–96" H × 24"–48" W

Bloom

Jun, Jul

Native to

AZ, CA, CO, CT and 36 more states

Pollinators

bees, beetles, flies

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Browse plants for this ecoregion

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American cow-parsnip is a large, dramatic native perennial that can reach 8 feet tall with massive umbrella-shaped white flower clusters in summer. This bold architectural plant has huge compound leaves and creates a striking focal point in the landscape. It prefers partial sun and consistent moisture to reach its full impressive size.

Growing American Cow-parsnip

Grow American Cow-parsnip in part sun and medium water. Mature plants reach 36 to 96 inches tall and spread 24 to 48 inches wide. Expect moderate maintenance to keep it looking intentional in a front yard.

In an HOA neighborhood

American Cow-parsnip takes more care to keep looking intentional in a front yard. Maintenance level: moderate. Consider it for backyard or mid-zone beds rather than the street edge.

Works well in: backyard only.

Extremely large size may appear uncontrolled
Can look messy when stems die back
May be confused with invasive giant hogweed

Wildlife value

The large white flower umbels attract diverse pollinators including native bees, beetles, and flies during its June-July bloom period. Its substantial size and abundant nectar make it particularly valuable for supporting pollinator populations.

Common questions

When does American cow-parsnip bloom?: American cow-parsnip typically flowers in June and July, producing large, flat-topped clusters of small white flowers held above coarse, broad leaves.
What pollinators visit American cow-parsnip?: Bees, beetles, and flies are frequent visitors to the wide, flat flower clusters, which offer easy access to nectar and pollen.
What growing conditions does American cow-parsnip prefer?: This forb does best in part sun with medium to consistently moist soil, and is often found along stream banks, wet meadows, and forest edges.
Is American cow-parsnip a shrub or a perennial forb?: It is a tall herbaceous forb, not a woody shrub, dying back to the ground each year and regrowing from its root system in spring.
Is American Cow-parsnip toxic to dogs?: Yes. American Cow-parsnip is listed as toxic to dogs by the ASPCA Animal Poison Control Center (aspca.org). If your pet has been exposed, call the ASPCA Animal Poison Control Center at (888) 426-4435.
Is American Cow-parsnip toxic to cats?: Yes. American Cow-parsnip is listed as toxic to cats by the ASPCA Animal Poison Control Center (aspca.org). If your cat has been exposed, call the ASPCA Animal Poison Control Center at (888) 426-4435.
Is American Cow-parsnip toxic to livestock?: American Cow-parsnip is listed as toxic to grazing livestock such as cattle, sheep, and goats (slight severity) by the USDA PLANTS Database. This is separate from pet (dog and cat) toxicity.
Is American Cow-parsnip HOA-friendly?: American Cow-parsnip takes more care to look intentional in a front yard. Consider it for backyard or mid-zone beds rather than the street edge.

These answers were drafted with an AI model from this plant's data. Verify care details with a local expert.

Native range data from vouchered herbarium specimen records and regional native plant society lists. Pollinator and host plant associations compiled from GBIF, iNaturalist, and published ecological literature.

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