Smartweed, Big Seeded Smartweed, Pink Knotweed, Pinkweed, Pennsylvania Smartweed
Persicaria pensylvanica

Family: Polygonaceae
Genus: Persicaria (per-sih-KAR-ee-uh) (Info)
Species: pensylvanica (pen-sill-VAN-ee-ka) (Info)
Synonym:Polygonum bicorne
Synonym:Polygonum mexicanum
Synonym:Polygonum mississippiense
Synonym:Polygonum pensylvanicum
Synonym:Persicaria mississippiensis

Category:

Annuals

Herbs

Height:

36-48 in. (90-120 cm)

Spacing:

18-24 in. (45-60 cm)

Hardiness:

Not Applicable

Sun Exposure:

Full Sun

Sun to Partial Shade

Light Shade

Danger:

Handling plant may cause skin irritation or allergic reaction

Bloom Color:

Pale Pink

Pink

Rose/Mauve

Bloom Time:

Late Spring/Early Summer

Mid Summer

Late Summer/Early Fall

Foliage:

Smooth-Textured

Shiny/Glossy-Textured

Other details:

May be a noxious weed or invasive

This plant is attractive to bees, butterflies and/or birds

Self-sows freely; deadhead if you do not want volunteer seedlings next season

Soil pH requirements:

4.5 or below (very acidic)

4.6 to 5.0 (highly acidic)

5.1 to 5.5 (strongly acidic)

5.6 to 6.0 (acidic)

6.1 to 6.5 (mildly acidic)

6.6 to 7.5 (neutral)

7.6 to 7.8 (mildly alkaline)

7.9 to 8.5 (alkaline)

Patent Information:

Non-patented

Propagation Methods:

From seed; direct sow outdoors in fall

From seed; winter sow in vented containers, coldframe or unheated greenhouse

From seed; stratify if sowing indoors

Seed Collecting:

Bag seedheads to capture ripening seed

Allow seedheads to dry on plants; remove and collect seeds

Properly cleaned, seed can be successfully stored

Regional

This plant has been said to grow in the following regions:

Prescott Valley, Arizona

Deer, Arkansas

New Milford, Connecticut

Demorest, Georgia

Leavenworth, Kansas

Benton, Kentucky

Melbourne, Kentucky

Brookeville, Maryland

Cumberland, Maryland

Vicksburg, Mississippi

Ogdensburg, New York

Orient, Ohio

San Antonio, Texas

show all

Gardeners' Notes:

1
positive
2
neutrals
3
negatives
RatingContent
Positive

On Jul 1, 2013, plant_it from Valparaiso, IN wrote:

Polygonum pensylvanicum is native to the U.S. and I can't get enough of the beautiful flowers, so it's a positive in my book.

Don't confuse this native plant with Polygonum persicaria. P. persicaria is a non-native invasive. You can tell them apart from their ocreas. The ocrea is a thin membranous sheath that encircles the stem at the base of each leaf petiole. The ocreas of P. persicaria have small (2mm) stiff hairs arising from the top. The ocreas of the native P. pensylvanicum do not.

Negative

On Jul 9, 2011, KyWoods from Melbourne, KY (Zone 6a) wrote:

I thought these were pretty when they showed up in one area, so I let them stay. Big mistake--now I am pulling them up everywhere! If you want these in a small area, make sure you pluck off the flowers before they go to seed!

Neutral

On Feb 28, 2009, NatureLover1950 from Vicksburg, MS (Zone 8a) wrote:

I like to find this weed when it's flowering in local fields. When the flowers are at the pink stage I clip a big bunch to use in dried flower arrangements. They not only dry well but hold their color very well.

Negative

On May 24, 2005, CaptMicha from Brookeville, MD (Zone 7a) wrote:

Me no likey.

This plant is a pest in recently disturbed earth, which means any new gardens or freshly dug up gardens.

Also pops up in the lawn.

Neutral

On Jan 17, 2005, JodyC from Palmyra, IL (Zone 5b) wrote:

This native annual plant is 1-4' tall, branching occasionally. It is more or less erect, often bending toward the light in partially shaded locations.

The flowers attract many kinds of insects, including long-tongued bees, short-tongued bees, wasps, flies, small butterflies, skippers, and moths. Almost all of these insects seek nectar. The caterpillars of several moths feed on the foliage of this smartweed and others, including Lithacodia synochitis (Black-Dotted Lithacodia), Lithacodia carneola (Pink-Barred Lithacodia), Haematopsis grataria (Chickweed Geometer; often flies during the day), and Dipteryia rosmani (Noctuid Moth sp.). The caterpillars of the butterflies Lycaena helloides (Purplish Copper) and Strymon melinus (Gray Hairstreak; eats flowers & buds) are occasion... read more

Negative

On Jan 2, 2005, melody from Benton, KY (Zone 7a) wrote:

An invasive weed that has the ability to reproduce itself from even the tiniest bit of stem. It grows in cultivated fields, gardens and damp meadows. Vast amounts of seeds are produced that have the capability of remaining dormant for quite some time.

The seeds are attractive to birds and wildlife, but so many of these plants are produced each year, there is no need to propogate it on purpose.

The sticky sap can cause irritation if it comes in contact with the skin, thus, the name Smartweed.