Key Facts
- Perennial herb in the carrot family with large compound leaves
- Umbel of white flowers arranged in flat topped clusters
- Native to much of North America and found in moist meadows and forest edges
- Sap can cause phytophotodermatitis resulting in painful blisters after sun exposure
- Reproduces primarily by seed and forms clumps from the root crown
- Prefers moist, fertile soils and full sun to part shade
Cow parsnip is a tall North American perennial in the carrot family valued for large compound leaves and flat topped clusters of white flowers, useful as a meadow or edge plant where moisture is reliable. Handle with care because the sap can cause painful phototoxic skin reactions when exposed to sunlight.
Identification
Stout stems bearing very large compound leaves and umbrella shaped white flower umbels make cow parsnip conspicuous in late spring and early summer. Plants typically reach about 3 to 8 feet tall with a mature spread of roughly 2 to 4 feet depending on site fertility and moisture.
Where to grow and best uses
Grow cow parsnip in moist meadows, along streambanks, and at forest edges where it can naturalize into clumps. Use it as a background or meadow accent in large plantings rather than a small garden specimen because of its size and the risk of sap burns.
Site and soil
Plant where soils are moist to mesic and rich in organic matter. The species tolerates clay and intermittent wetness but declines in extended drought. Provide full sun to part shade for best flowering and vigor.
Planting time and spacing
Establish cow parsnip from seed sown in fall or spring, or move small clumps by dividing the root crown. Allow 2 to 4 feet between plants to accommodate natural clumping and to reduce competition for light.
Watering and maintenance
Keep soil consistently moist during establishment and the growing season. Plants in dry soil become stunted and may die back. After flowering, cut back stems to the crown to tidy the patch and to reduce seed production.
After flowering and controlling spread
Cow parsnip reproduces mainly by seed and forms colonies from the root crown. Prevent unwanted spread by removing or cutting flower heads before seeds mature and by pulling young volunteers. Division of established clumps gives a controlled way to relocate plants.
Safety and toxicity
The sap contains furanocoumarins that cause phytophotodermatitis. Avoid skin contact, wear gloves and eye protection when cutting or handling plants, and wash exposed skin promptly. Do not feed the plant to livestock or pets.
Seasonal notes
Blooming is commonly from May to July in the Northern Hemisphere and shifts earlier or later with latitude and elevation. Plants die back to the root crown in winter and resprout in spring in most temperate areas.
Frequently asked questions
- How fast does Cow parsnip grow?
- Plants commonly achieve their typical height range of about 3 to 8 feet in a single season depending on soil moisture and fertility.
- Is Cow parsnip invasive?
- The species readily self seeds and forms clumps that can expand into stands in suitable moist sites so monitor volunteers and remove flower heads to limit spread.
- What hardiness zones will Cow parsnip grow in?
- It is generally associated with USDA zones about 3 to 7 and performs best where winters are within that temperate band.
- When should I remove seed heads?
- Cut or remove flower heads before seeds form to prevent local reseeding and reduce spread.
- How do I handle the plant safely?
- Wear gloves and eye protection, avoid skin contact with sap, and wash any exposed skin promptly if sap makes contact, especially before going into sunlight.
Related Plants
