Persicaria

( per - sih - KAR - ee - ah )

At-A-Glance Information

Commonly referred to as Knotweed, Fleeceflower or Smartweed, this genus includes flowering perennial plants that need full sun to partial shade and regular water to perform well. They are considered easy to grow and have handsome foliage. Spikes of flowers bloom in shades of pink or white. Use Persicaria plants in mixed beds and borders, in depressions or moist areas of the garden, around water features, or as members of prairie, meadow, informal, cut flower, or cottage garden landscapes. They can be mass-planted on hillsides to provide erosion control, and can also serve as groundcover. Take care when planting these flowers in the landscape, as ingestion of plant parts of certain species can be fatal to livestock and mildly toxic to humans, cats and dogs.

Persicaria Species and Varietals

The genus Persicaria is a member of the plant family Polygonaceae and includes 132 species. The plants in this genus are related to those in Polygonum (Knotweed), Rumex (Dock) and Rheum (Rhubarb). The best growing zones for Knotweed vary depending on the species. For more information, see the descriptions below. To find your zone, click here: Zone Map.

Persicaria amphibia (Longroot Smartweed, Water Knotweed, Water Smartweed, Amphibious Bistort)
These plants are native to much of North America, Asia, Europe, and some areas in Africa. It is considered a weed in some parts of the world. These plants prefer wet habitats, like ponds, streams, and marshes. They can be fully aquatic, growing submerged or floating in bodies of water. Flowers are typically in shades of pink. Best in USDA hardiness zones 3-10.

Persicaria bicornis (Pink Smartweed, Two-Horned Smartweed)
These plants are native to areas in the central and southwestern United States, and is an annual planting that reaches up to 6 inches tall. Pink Smartweed is suited for USDA hardiness zones 3-9, and produce pink flowers with pink or red anthers and are present from June through October. Blooms are fringed. Leaves are green and narrow. These plants typically grow in ditches or other disturbed areas, or along the shores of ponds and reservoirs.

Persicaria bungeana (Prickly Smartweed, Bunge's Smartweed)
These annuals are common weeds of soybean fields in the midwestern United States, and forms a small plant that reaches between 11 and 31 inches tall when mature. Leaves are pale green with a reddish tint, and flowers are pink to cream-white. It is native to China, Manchuria, Korea, and Japan and is considered a weed of agricultural fields in the midwestern United States.

Persicaria capitata (Polygonum capitatum) (Pink-Headed Persicaria, Pink Bubble Persicaria, Japanese Knotweed, Pink Knotweed, Pinkhead Smartweed)
This species is suited for growing in USDA hardiness zones 7-10 or Sunset growing zones 8, 9 and 12-24, and is native to the Himalayas. This cool-weather loving plant forms a trailing groundcover 3-6 inches tall. Leaves are bronze when new, and mature to green blushed with pink. Stems and flowers are pink, and this plant will bloom year-round in mild climates. Best in containers. This species is considered invasive in Hawai'i, California, and regions of the southern United States, Australia, South Africa, The Azores and Ireland.

Persicaria chinensis (Polygonium chinense) (Creeping Smartweed, Chinese Knotweed, Flowery Knotweed, Huǒ Tàn Mǔ, 火炭母)
These plants are native to India, China, Japan, Indonesia, Malaysia, and Vietnam. It is used in its native range as a traditional medicinal plant. These perennial climbing plants reach between 6.5 and 10 feet tall when mature, and produce small white to pink flowers. Fruits that follow are edible but quite sour. Chinese Knotweed is considered invasive in Hawai'i, Australia, New Zealand, Jamaica, Madagascar, and Réunion.

Persicaria decipiens (Slender Knotweed, Willow Weed, Snake Root, Spotted Smartweed)
These trailing plants reach about a foot tall and have narrow spear-shaped green leaves. They grow well in USDA hardiness zones 9-13. Flower spikes support pink flowers from November through June, peaking in February. Plants die back in wintertime and regenerate after the first rains. They are native to Australia and Asia and are considered invasive in Madagascar, regions of Europe, and the Canary Islands.

Persicaria hydropiper (Polygonum hydropiper) (Arse Smart, Tade, Water Pepper, Marshpepper Knotweed)
These plants are widespread across Australia, New Zealand, Asia, Europe and North America, where they grow in damp areas and shallow waters. Some varieties are cultivated for culinary purposes; they have a pungent flavor (hence the common name Water Pepper). Water Pepper grows well in USDA hardiness zones 5-9 and is considered invasive across much of North America, Australia, and New Zealand.

Persicaria lapathifolia (Polygonum lapathifolium) (Pale Persicaria, Pale Smartweed, Curlytop Knotweed, Willow Weed, Dock-Leaved Smartweed)
These variable species of Knotweed is native to most of the world, and is considered a weed in Europe. Stems are erect and reddish, holding tiny pink flowers. Foliage typically has darker markings towards the center of leaves. These plants are typically found growing on seashores and disturbed areas, such as gardens, agricultural lands, waste grounds, and roadsides. They are suited for USDA zones 5-9 and are considered invasive in South America, southern Africa, Europe, and the United Kingdom.

Persicaria longiseta (Oriental Lady's Thumb, Bristly Lady's Thumb, Asiatic Smartweed, Long-Bristled Smartweed, Low Smartweed, Asiatic Waterpepper, Bristled Knotweed, Bunchy Knotweed, Tufted Knotweed)
These plants are native to Asia, and have been introduced to North America and Europe, where it is typically considered a weed. These annuals reach between 12 and 32 inches long, and have hairless, branching stems. Inflorescences reach up to 3.2 inches long and hold many small pink flowers. This species is highly invasive in much of the eastern United States, southeastern Canada, and regions of Europe.

Persicaria odorata (Vietnamese Coriander, 越南香菜, Ram, Laksa Leaf, Vietnamese Cilantro, Phak Phai, Praew Leaf, Hot Mint, Cambodian Mint, Vietnamese Mint)
These herbs are used extensively in southeast Asian cuisines as fresh garnish or seasoning. They have a flavor profile that blends Cilantro, Mint, and Citrus with a peppery aftertaste. They grow well in warm, damp conditions and reach up to 24 inches tall and wide. Tops of leaves are dark green with spotting, and undersides are burgundy-red. Vietnamese Coriander grows well in USDA hardiness zones 5-11. It is considered invasive in tropical and subtropical regions of Australia and southeast Asia.

Persicaria orientalis (Kiss-Me-Over-The-Garden-Gate, Prince's Feather, Princess Feather, Prince's Plume)
These plants are native to Eurasia, and is widely cultivated and naturalized in many places in the world. Leaves are simple and green, and flower inflorescences are somewhat drooping and various shades of pink. This species grows well in USDA hardiness zones 1 through 12. Prince's Feather is considered invasive in New England and the southeastern region of the United States.

Persicaria perfoliata (Polygonum perfoliatum) (Mile-a-Minute, Devil's Tail, Giant Climbing Tearthumb, Asiatic Tearthumb)
This species forms a trailing herbaceous annual vine with barbed stems and triangular leaves. It is native to temperate and tropical areas of Asia and produces reddish stems, green foliage and small white flowers. Metallic blue fruits are edible raw, with a flavor similar to Grapes or mild Blueberries. Tender young greens are used in salads and soups. They are considered highly invasive in the mid-Atlantic, northeast, and midwestern regions of the United States.

Persicaria tinctoria (Chinese Indigo, Japanese Indigo, Dyer's Knotweed)
These plants are a source of indigo dye in many areas of Eastern Europe and Asia. They produce green leaves (the source of the dye). Flowers are bright pink with white bases, and stems are typically red. This species is suited for growing in USDA hardiness zones 10-12.

Persicaria virginiana (Polygonum virginianum, Tivara virginiana) (Jumpseed, Virginia Knotweed, Woodland Knotweed)
This species is best in USDA hardiness zones 3-8 or Sunset growing zones 2-9 and 14-17 and is native to the eastern areas of North America and Asia. It spreads by creeping rhizomes. 'Painter's Palette' has marbled foliage, as does 'Variegata' (pictured). Plants reach up to 1 to 4 feet tall with flower stalks extending above the foliage and form clumps 2-4 feet wide.

Caring for Persicaria

Persicaria plants grow well in a space that receives full sun to partial shade. The amount of sun these plants prefer depends on the species grown; for specific information, see the species descriptions above. Ensure that soil is well-draining, moderately fertile, and has a pH of between 5.5 and 7.5 (though they are not typically too picky about soil acidity). If local soils are particularly poor in nutrients or do not drain well, make sure to amend the planting area with plenty of organic compost before installing. Water newly planted Persicaria regularly to help it develop a strong root system. At maturity, the amount of water these plants needs varies by species. Do not allow soil to dry out completely between waterings. Apply a thick layer of mulch around the planting area to suppress weed growth, maintain consistent soil temperatures, and increase soil moisture retention.

Fertilize yearly in early springtime with an application of 2 inches of compost around the base of plants. Pull mulch back before applying, work the compost gently into the soil a bit, water it in, and then replace mulch. These plants are not heavy feeders, and this should be sufficient to provide the necessary nutrients for the active growing and flowering seasons. Prune to remove spent flowering heads and any dead, damaged, or diseased foliage. If you are looking to propagate these plants through harvesting and sowing seeds, leave a few flower spikes alone to mature. There are annual and perennial species of Persicaria. Annuals are typically pulled at the end of the growing season and composted or left in place to enrich the soil, replaced in the next year with new plants. Perennial species can survive for 3-5 years in the garden before needing to be replaced.

Propagation

Persicaria can be propagated either by division or from seed. To ensure that your propagated plant will have the exact same qualities and characteristics as the parent plant, use the division method. If you would like to experiment and see what plant you can grow from seed, just keep in mind that it will not necessarily be the same as the parent plant. To propagate your Persicaria, follow the instructions below:

Propagating Persicaria by Seed

Keep in mind that the plant you get from seed will not necessarily mimic all of the characteristics of the parent plant. To propagate by seed, you will need a paper bag, a pot or tray filled with well-draining compost or other organic material, a spray bottle and a fork. The best potting medium for seed germination is a light blend of 1/3 pasteurized soil or compost, 1/3 sand, vermiculite or perlite, and 1/3 coconut coir or peat moss.
Harvest your seeds. The seed heads on plants are pretty easy to spot, they're left behind after flowers have faded. Once they have dried out and begun to split open, you can harvest the seeds inside. Cut them off of the plant, placing them in a paper bag. Harvest as many as you can, and place the paper bag in a dry, cool, dark area. They will continue to split open and release the seeds contained inside. Once they have been released, take them out of the bag and put them in a container so you can work with them.
In either late winter or early springtime, get your container prepared. Water your prepared seed tray or pot filled with soil, and ensure that good drainage is occurring. Place your seeds in your prepared pot or seed tray about a quarter inch to a half-inch under the soil surface. Cover them with soil and water with your spray bottle. Place your tray of seeds in a warm area that receives bright, indirect light. A greenhouse is the most ideal climate, but a planting tray inside a window will do as well. Germination usually takes 10-14 days from sowing. Once you begin to see seedlings sprout and they are able to be handled, transplant them to their own individual 3-inch pots, filled with the same potting medium as described in Step 1. Loosen the seedlings from the potting medium by digging down with the tines of your fork about an inch and a half, gently working the seedling up until it is out. Then, replant the seedling in its individual pot.
Keep the seedling's potting medium moist, but not wet, by spraying the soil with your spray bottle. Keep your new plant in an area with bright light (though not direct sunlight) and temperatures between 65 and 72 degrees Fahrenheit. Ensure that the soil stays moist, but not wet, until the next spring (after the danger of frost has passed), when you can transplant it to its new home.

Propagating Persicaria by Division
This type of propagation is relatively simple; you will need a clean shovel, mulch, fresh soil, compost and pots (only necessary if you will be saving divided plants for transporting elsewhere). Division is best done in very early spring (after the plant has entered dormancy, but before it has begun its new spring growth), and needs to be done every few years regardless of whether you have the goal of propagating the plants for best performance. To propagate by division, follow these steps:

Using a shovel, dig up your existing plant. Start from the outside and work your way in to avoid damaging the root(s). Once you have worked it up out of the ground, lay it out.
Start to tease apart the roots with your fingers. Once the roots are untangled, separate your plant into segments, ensuring that each one has at least one thick root section attached.
Prepare your pot(s) or new planting site(s) with amended, well-draining soil. You can either bring in new soil or simply amend your existing soil with compost to complete this task. Then, plant your divisions and water thoroughly.
Apply a thick layer of mulch over the new planting to protect it from cold weather as it acclimates to its new home. Then, enjoy watching it sprout in the next growing season.

Persicaria seed pods will develop where flowers once bloomed.

Persicaria seeds are typically small and black to reddish-brown in color.

Problems and Pests

Certain Persicaria species are considered invasive in some regions; see the species descriptions above for more information. Check with local authorities before planting. Persicaria plants are typically resistant to pests and diseases in the garden, though they can have issues from time to time with: