Pennsylvania smartweed
Polygonum pensylvanicum
Last reviewed: October 2026
Pennsylvania smartweed (Polygonum pensylvanicum) is a annual forb native to AL, AR, AZ, CA and 42 more states. It blooms in July, August, September, and October. The flowers draw native bees, flies, and butterflies.
Toxicity unknown
Pennsylvania smartweed (Polygonum pensylvanicum) is not listed by the ASPCA Animal Poison Control Center (opens in new tab) or the other sources we check, so we have no verdict for it either way. Absence from those lists is not a clearance. If your pet shows symptoms after eating any plant, call the ASPCA at (888) 426-4435.
Light
full sun
Water
high
Size
24"–48" H × 18"–30" W
Bloom
Jul, Aug, Sep, Oct
Native to
AL, AR, AZ, CA and 42 more states
Pollinators
native bees, flies, butterflies
Before you buy
Your city may pay you to plant this
Cities and water utilities offer rebates for replacing lawn with native and water-wise plants. We track 458 programs across 44 states, each with a link to the provider and the date we last checked it.
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Browse plants for this ecoregion
A vigorous annual with jointed, reddish stems and dense, bristly spikes of bright pink flowers. It grows in wet, disturbed ground and along pond edges, often forming dense stands by late summer.
Growing Pennsylvania smartweed
Grow Pennsylvania smartweed in full sun and high water. Mature plants reach 24 to 48 inches tall and spread 18 to 30 inches wide.
Wildlife value
Its abundant late-season flowers provide nectar for native bees, flies, and butterflies, and the seeds are an important food source for waterfowl and songbirds.
Common questions
- How much sun does Pennsylvania smartweed need?
- Pennsylvania smartweed grows best in full sun conditions.
- When does Pennsylvania smartweed bloom?
- Pennsylvania smartweed blooms in July, August, September, and October.
- Where is Pennsylvania smartweed native?
- Pennsylvania smartweed (Polygonum pensylvanicum) is native to AL, AR, AZ, CA and 42 more states, per the World Checklist of Vascular Plants (Kew).
- What pollinators does Pennsylvania smartweed attract?
- Pennsylvania smartweed draws native bees, flies, and butterflies.
Native range data from the World Checklist of Vascular Plants (Kew). Pollinator and host plant associations compiled from GBIF, iNaturalist, and published ecological literature.
If something looks wrong
Common plant problems, and what to check first
These come up on almost any plant. Each guide lists the likely causes in the order they are worth ruling out, with one thing to check before you act on any of them, and links to the source it came from.
- It is dying right after planting
- Leaves turning yellow
- Wilting even though I watered it
- Brown crispy leaf tips
- Bugs on the plant
Ready to grow Pennsylvania smartweed? Add it to your garden in Pollinator Patch to track it and get season-by-season care guidance.