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A Colorful and Cohesive Tan for the Winter Garden

by Bruce Crawford, Manager of Horticulture, Morris County Park Commission

Winter interest is a very personal topic. What one gardener finds attractive another may find mediocre at best. I have long been a fan of tan foliage in winter, a color I think most people do not associate with the term attractive nor even with the term living! Interestingly, the color tan is a mixture of the very lively hues of green and red. For some plants the tan foliage of winter has a touch more red, making the foliage appear more glowing and warm for the winter garden. A low maintenance groundcover I have long appreciated for its warm winter foliage is Persicaria affinis, commonly called Himalayan Bistort or Lesser Knotweed (as seem in Picture 1).

Zoom in Persicaria affinis.
Picture 1: Persicaria affinis in June.

Might I first mention—unlike many of its ill-mannered relatives—Persicaria affinis is not invasive! It is a member of the Polygonaceae or Buckwheat family with around 130 species native to nearly all regions throughout the world, although it is most abundant in the northern hemisphere. As the common name implies, Himalayan Bistort is native to the mountainous regions of Afghanistan and Eastern Nepal into China at elevations of 9,500–15,500 feet.

Secondly, and sadly for my limited memory, the botanical name I first learned for Himalayan Bistort is no longer the name of the plant! For well over a century, the plant was known as Polygonum affine, with the genus name properly described in 1753 by the Swedish botanist Carl Linnaeus (1707–1778). The name Polygonum comes from the Greek Polu for many and Gonu for knees, referring to the many swollen joints along the stem. At each joint, the orientation of the stem changes, resembling the flexing of a leg at the knee. The joint is also the point of leaf emergence and is covered by a membranous sheath called an ochrea. As a side note, Linnaeus did not actually create the name, but rather adopted it! For centuries the name Polygonum was associated with a medicinal plant (Polygonum perfoliatum) with swollen nodes known for reducing swelling and bleeding.

The species of Polygonum affine was initially described in 1825 by the Scottish Botanist, David Don (1799–1841). Although he never traveled to the Himalayan region, he studied plants collected by the Scottish physician and botanist Francis Buchanan Hamilton (1762–1829) during his excursions to Nepal in 1802–1803 and from the Danish physician and botanist Nathaniel Wolff Wallich (1786–1854). From 1820–1821 Wallich explored Nepal and worked with artists to produce exquisite images of the plants he discovered, all of which aided Don in describing this particular species. The epithet of Affine is from the Latin meaning 'related' or 'similar to', describing how this species appears similar to the medicinal Polygonum.

Zoom in Himalayan Bistort.
Picture 2: Himalayan Bistort in Mid-November with frost.

This name remained unchanged until the latter part of the 20th century when it became apparent the genus Polygonum was polyphyletic, meaning the various species within the genus did not have one evolutionary lineage of ancestors, but several. In other words, it had not one but several different family trees under the umbrella of one genus and that genus needed to be split into several unique genera for each family tree. The membranous ochrea was in fact one of the distinguishing features used to separate the various unique genera lumped under Polygonum. In 1988 some of these family trees were teased out by the Belgian botanist Louis Ronse de Craene (1962– ) and Himalayan Bistort was renamed Persicaria affinis. To lend further confusion to this story, Persicaria was not a new name. Rather, it had been described in 1754 by the Scottish Horticulturist and Botanist Philip Miller (1691–1771). The name comes from the Latin Persicum for peach, referencing how the leaves resemble that of a peach tree (as seen in Picture 2).

The common name of Himalayan Bistort obviously reflects its native geographic territory, while the name of Bistort comes from the Latin Bis for twice and Torta for twisted. This term may describe how the roots are often twisted into a mass or how the swollen nodes on the stem resemble twisted knots, which also led to the term Knotweed. Polygonaceae is still a subject of much study and it is possible the genus name might yet change again. In fact, the name Bistorta affinis was proposed by the American botanist Edward Lee Greene (1843–1915) in 1904 and although it is seen in some literature as the accepted name, it is certainly not universally accepted. Fortunately, the plants' name does not impact the beauty nor the garden worthiness of this plant.

Zoom in Persicaria affinis 'Dimity' foliage.
Picture 3: Tan foliage in late March.
Zoom in Persicaria affinis in April.
Picture 4: Newly emerging foliage in late April.

I am a huge proponent of groundcovers. Their blooms and texture can enhance shrubs or taller growing herbaceous materials, while reducing the likelihood of weed growth. As we well know, less weeding also benefits the weary backs of many a gardener! Persicaria affinis has trailing stems allowing it to creep along the ground, with the basal foliage reaching heights of 4–6". It spreads at a moderate rate, expanding from 6" to 18" in diameter over the course of several years and if planted 18" apart, it will form a dense mat in 3–5 years (Picture 3).

Zoom in Persicaria affinis 'Dimity'.
Picture 5: Close-up of flowers in September.

Much as the genus name implies, the 3–4" long foliage is shaped much like that of a peach with the elliptical leaves coming to a point at either end. The central mid-rib is light grey to white, while the remainder of the upper surface is an attractive medium green. Typical to plants growing in windy and mountainous regions, the bottom of the leaf has a glaucus or waxy coating, giving it a light blue or grey appearance. This coating helps to protect the plant from losing excessive amounts of water, making it more drought tolerant. Come the heavy frosts of autumn, most of the foliage develops a showy orange or red coloration while other leaves remain green (as seen in Picture 2). The central midrib of many of the leaves, even those that are still green, also turns red making for a particularly showy autumn display.

Come late fall, all the leaves transition to a reddish tan and remain firmly attached to the stems, covering the ground throughout winter (as seen in Picture 3). Come spring, the fresh green foliage emerges from the jointed stems (Picture 4), displaying a strong white central vein and red overtones along the leaf margins. The new leaves cover and conceal the previous year's tan foliage, which remains firmly attached to the stems. This benefits the gardener since nothing needs to be cut back nor any of the previous year's foliage removed. The older foliage slowing breaks-down under the new foliage and effectively serves as a water retaining mulch. Clearly, this also eliminates the effort and expense of adding any additional mulch. A very environmentally sustainable plant!

Come June through September, plants develop 10–12" tall floral spikes with the top 2–3" bearing dense displays of flowers arranged radially around the central stem (Picture 5). The flowers typically consist of 5 light pink sepals with 8 pollen releasing stamens, although I have seen flowers with 6 sepals and 10 stamens (Picture 5). The sepal is the leafy bract that covers the flower bud and, in many plants, it is modified to assume the insect attracting role of petals. Two to three arching female pistils protrude from the center (Picture 5). As the flowers age, the sepals transition to a deep attractive rusty-red as seen in Picture 6, providing the plant with a two-tone appearance since new spikes of light pink flowers continue to be produced. The remnants of the floral stalk often remain standing into winter, although I do not believe they provide the winter interest some authorities suggest.

Zoom in Persicaria affinis 'Superba'.
Picture 6: Old and new flower spike in June.

As previously mentioned, Himalayan Bistort is not invasive although the plants will gradually spread via the creeping stems and may need to be curtailed if they exceed their boundaries. Plants grow best in full sun and in moisture retentive yet well-drained soils in zones 5–8. Plants will tolerate light shade, especially in more southern regions where the coolness of the shade proves beneficial. I have had plants decline in hot microclimates containing well-drained soils in full sun that is compounded by heat reflected from nearby pavement.

Plants look great when paired with the dark purple foliaged Ophiopogon planiscapus 'Nigrescens' (Mondo Grass) as seen in Picture 7 or purple foliaged forms of Ajuga reptans (Bugle Weed). In these cases, it is the artistic hand of the gardener that keeps the plants in check from overwhelming each other. The cultivar 'Superba' provides pale pink or nearly white flowers to start, transitioning to deep rose red and may be synonymous with the form named 'Dimity'. 'Border Jewel' is another attractive form that looks similar to the previous two forms. The one advantage to the selections is their tendency to be more floriferous and are certainly worth seeking out.

Clearly, Persicaria affinis has a lot to offer the garden throughout the year, including the winter. To me, the winter garden should be a blend of various shades of tan complimented with a backbone of evergreens. Many gardeners may not agree but, the more you work with various tans the more you learn of their beauty and ability to unify the winter garden. Himalayan Bistort provides a magical touch of texture and color that will convince even the most questioning of gardeners that tan is not mediocre, but a cohesive color for the winter garden!

Ophiopogon planiscapus 'Nigrescens' with Persicaria in November.
Picture 7: Ophiopogon planiscapus 'Nigrescens' with Persicaria in November.