The Persicaria pensylvanica is native to parts of North America. It can reach up to 2 m tall with upright and ribbed stems that can be branching or unbranched. There may be a dark blotch on the leaf blade and its flowers have five pinkish or greenish sepals each only a few millimeters long. The plant’s fruit serves as an important source of food for almost 50 species of birds.
I. Appearance and Characteristics
Persicaria pensylvanica (syn. Polygonum pensylvanicum) is a species of flowering plant in the buckwheat family, Polygonaceae. It is native to parts of North America, where it is widespread in Canada and the United States. It has also been noted as an introduced species in parts of Europe and South America. Common names include Pennsylvania smartweed and pinkweed.
Pennsylvania smartweed is a variable annual herb reaching 10 cm (3.9 in) to 2 m (6.6 ft) tall. The upright, ribbed stems are branching or unbranched. The lance-shaped leaves have a short petiole and a blade about 4–17 cm (1.6–6.7 in) long, sometimes up to 23 cm (9 in). The blade may be marked with a dark blotch. The brownish ochrea at the base is up to 2 cm (0.79 in). The inflorescences grow at the top of the stem and from the leaf axils. The flowers have five pinkish or greenish tepals each a few millimeters long.
This plant grows in moist, disturbed habitat types, such as ponds, reservoirs, riverbanks, irrigated fields, and ditches.
This plant is an important part of the habitat for waterfowl and other birds, which use it for food and cover. At least 50 species of birds have been observed feeding on the seeds, including ducks, geese, rails, bobwhites, mourning dove, and ring-necked pheasant. The seeds and other parts are eaten by mammals such as the white-footed mouse, muskrat, raccoon, and fox squirrel.
II. How to Grow and Care
Sunlight
Pennsylvania smartweed thrives in full sun environments, receiving at least six hours of direct sunlight daily. Its preference for such conditions significantly enhances its growth, fostering robust health and vibrant foliage. While Pennsylvania smartweed possesses a degree of tolerance to light variations, prolonged exposure to less-than-ideal light levels—such as substantial shade—may result in reduced vigor and sparse flowering. In an outdoor setting, Pennsylvania smartweed should be planted in areas that are bathed in unfiltered sunlight, away from larger plants or structures that could create excessive shade. Adaptive traits such as leaf orientation help maximize light absorption, ensuring Pennsylvania smartweed’s resilience in diverse lighting circumstances.
Watering
Thriving in its native moist environments, pennsylvania smartweed exhibits a strong preference for consistent moisture levels. This species is well-adapted to the wetlands it commonly inhabits, showing resilience in saturated conditions. Watering should be maintained at once every week to mimic these natural damp surroundings. As an outdoor plant often found along waterways, Pennsylvania smartweed benefits from regular rainfall patterns which support its vigorous growth during the active season.
Fertilizing
Fertilizing Pennsylvania smartweed is vital for robust growth and bloom enhancement. Employ balanced nutrition fertilizers in spring for all-around vitality and switch to high-nitrogen variants in early summer to boost leafy expansion. Apply quarter-strength solutions bi-weekly during active growth, tapering off in late summer. For seedlings or young plants, dilute to half strength to prevent root burn. Seasonal adjustments and moderate quantities are crucial for Pennsylvania smartweed’s health. Always water soil before application to aid nutrient absorption and minimize root shock.
Planting Instructions
As it is an annual, Pennsylvania smartweed is usually planted using its seeds. In protected areas or in regions with warm winters, the seeds can be planted as early as fall. If you intend to germinate them directly outdoors, you may wait for the final frosts of early spring to pass. The seeds can be buried in about 1 – 2 inches (2.5 – 5 cm) of soil in drawdown zones or in patches with supplementary irrigation. Keep in mind that consistent moisture is necessary for germination.
To facilitate the development of a uniform Pennsylvania smartweed stand, this species may need to be re-planted annually. Harrowing the soil can aid in the natural re-establishment of its previously grown stands. For purposes associated with supporting wildlife, this species’ seeds can be distributed around the drawdown zones of water features or in mudflats. Once the seedlings reach a height of around 6 inches (15 cm), they can be re-flooded. The duration of each flooding period would depend on the maturity of the smartweed stands, with mature stands tolerating longer exposure periods to shallow water.
Over time, mature smartweed stands should begin to generously produce seeds, which will naturally become lodged into bottom substrates and grow dormant through winter. A fair portion, particularly those that are closer to exposed topsoil, are likely to germinate as soon as temperatures rise and waters recede.
Overwintering
As Pennsylvania smartweed naturally occurs as an annual plant, it does not tolerate cool temperatures in winter. Its stands are most likely to die back once they have released hundreds to thousands of seeds. The seeds will remain dormant through winter, after which they will germinate if spring conditions are suitable. The seeds can be left in the ground and will not adversely be affected by being submerged or buried through winter.
III. Uses and Benefits
- Medicinal uses
Native Americans have various uses for the plant. The Chippewa use it for epilepsy. The Iroquois use it for horse colic. The Menominee takes a leaf infusion for hemorrhage of blood from the mouth and postpartum healing. The Meskwaki use it on bleeding hemorrhoids.
IV. How to Solve Trouble
Because of smartweed’s ample seeding ability, step one in controlling an outbreak is removing plants before the flowers have a chance to set seed and fuel ongoing outbreaks.
Plants are fairly easy to pull, hoe, or dig out since they’re new plants each season. Just try to remove all of the underground rhizomes and rooting points to head off regrowth.
Smartweed is also susceptible to several readily available weed-killers, so spraying is another option. Check product labels for usage directions and to make sure Pennsylvania smartweed is listed.
In sidewalk cracks, paver patios, and other non-flammable surfaces, flame weeders can be used to kill smartweeds with heat.