annualN. America Native

Pennsylvania Smartweed

The Story

Plant Bio

Persicaria pensylvanica is an upright to sprawling summer annual herb native to moist, disturbed habitats and wetlands across North America. The plant features lanceolate leaves on branching stems with characteristic swollen nodes.

This species produces dense, upright terminal spikes of tightly packed pink, rose, or white flowers on glandular stalks. It is distinguished from similar smartweeds by its lack of a prominent bristle fringe at the summit of the sheathing stipules.

Uses & Benefits:

Dense, upright spikes of pink, rose, or white flowers provide color in damp areas from summer to fall.

Thrives in wet, disturbed clay soils where other garden plants struggle to establish.

Provides critical high-energy seeds for waterfowl, game birds, and songbirds, while flowers attract native bees, wasps, and butterflies.

Essentials

At a Glance

Plant Type

Annual

Height

48"

Width

24"

Light

Full Sun, Partial Sun

Zones

4, 5, 6, 7, 8

Water

High

Humidity

High

Lifespan

Annual

Native To

North America

Toxicity

Skin Irritant

Bloom period

Summer – Autumn

In flower about 6 months of the year

Planting

How to Grow

Sow seeds directly onto moist, disturbed soil in full sun to partial shade during spring.
Maintain consistent soil moisture, as seedlings thrive in damp floodplains, clay, or silt.
Allow the plants to flower and set seed naturally through summer and fall to ensure next year's crop.
Monitor the area in subsequent springs to manage self-sown seedlings and prevent unwanted spreading.

Pro Tip

To distinguish this species from the invasive lady's-thumb, check the sheathing stipule at the leaf node; this native species lacks a fringe of long bristles and features glandular hairs on the flower stalks.

Keep It Thriving

Care Guide

Do

Sow seeds in consistently moist, rich soils or wetland margins.
Provide full sun to partial shade to maximize flower spike production.
Allow the annual plants to die back naturally after a hard freeze.

Don't

Do not apply supplemental fertilizers, as the plant thrives in unamended soils.
Do not allow the soil to dry out completely during prolonged dry spells.
Do not handle the sap without gloves if you have sensitive skin, as it can cause minor irritation.

Seasonal Care Calendar

Task	Jan	Feb	Mar	Apr	May	Jun	Jul	Aug	Sep	Oct	Nov	Dec
Pest Check
Plant
Propagate
Spring Cleanup

Watch Out For

Pests & Diseases

Common Pests

Common Diseases

In the Garden

Landscape Uses & Companions

Landscape Uses

Rain GardenBog GardenNative RestorationWildlife Forage Plot

Companion Plants

Chelone glabra Mimulus ringens

Multiply

Propagation Methods

Good to Know

Common Questions

Pennsylvania Smartweed questions

What zones can Pennsylvania Smartweed grow in?

Pennsylvania Smartweed is hardy in USDA Zones 4–8. Inside that range it survives winter in the ground; outside it, grow it as an annual or a container plant you protect.

When does Pennsylvania Smartweed bloom?

Pennsylvania Smartweed typically blooms in summer through autumn. Exact timing shifts a week or two with your zone — Sow's bloom calendar maps it to your garden.

Does Pennsylvania Smartweed need full sun?

Pennsylvania Smartweed does best in full sun to part shade. In hot climates, afternoon shade keeps blooms fresher longer.