Persicaria: how to grow persicaria and the best cultivars

By Daisy Bowie-Sell

Published: Sunday, 22 May 2022 at 12:00 am

Until recently, the genus that we now know as Persicaria used to sit within a much broader genus called Polygonum. As with so many other genera, molecular studies conducted this century have blown it apart into smaller constituent genera, including Polygonum, Fallopia and Fagopyrum. By a happy accident, most of the pre-eminent horticultural species now reside in one genus, Persicaria, although this is by no means completely settled.

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Persicaria ‘Taurus’
© Jason Ingram

The broader grouping contained some plants of infamously expansive vigour, including Russian vine (now Fallopia baldschuanica), and Japanese knotweed (Fallopia japonica). They may have damned some of their better-behaved cousins by association; however, although many of the species recommended here display a robust constitution and an agreeable self-sufficiency, they are all fairly easy to control when required.

Persicaria contains a broad variety of versatile garden plants, from vibrant, flowering dynamos and statuesque landscape plants to denizens of shady corners with atmospheric foliage.

Persicaria amplexicaulis can be considered among the most floriferous of cultivated plants available to gardeners in temperate regions, and breeding has spawned a wide variety of cultivars in vivid shades of a spectrum between crimson and scarlet, although for the faint of heart there are also some white and soft pink-flowered cultivars.

Its late season, spanning four months of intense flowering effort from July to October, combined with its general hardiness, versatility and natural charm, has won it an important place in the plant catalogues of the New Perennial Movement as well as in more traditional gardening paradigms. The versatility of the species is highlighted by Piet Oudolf’s planting at the Hauser & Wirth gallery in Somerset. Discover more about Persicaria below.

What is Persicaria?

A varied and versatile genus of around 100 species of robust and colourful perennials. Along with other members of the Polygonaceae family, they are commonly known as knotweed with the self-seeding Persicaria virginiana also known as jumpseed.

Origins of Persicaria

Persicaria are found in pretty much every country worldwide. The species covered here are found in a wide area emanating from the Himalayan region, while Persicaria virginiana is widespread throughout eastern North America.

When does Persicaria flower?

Most of the species featured here will flower from July to September or October; some species have a late flourish of blooms in September but these may be considered primarily as foliage plants.

Size

From 30cm to 2.5m, Persicaria have a general preference for rich soil and sun, with a few exceptions, but most species are adaptable.

Persicaria hardiness

Most species are hardy to -20ºC with a hardiness rating of RHS H6 to H7, and are generally suitable for gardens within USDA zones 4a to 8b.

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Persicaria amplexicaulis ‘Firedance’
© Dianna Jazwinski

How to grow Persicaria

Persicaria cultivation

The various species within the genus Persicaria are rather varied in their garden uses and cultivation requirements, but they tend to have in common a completely robust approach to life and will generally flourish with a minimum of fuss. Slugs and snails may make an impression on the foliage of Persicaria virginiana and its cultivars, but even they are not bothered too much. In general, the gardener’s problems when dealing with the genus are more likely to concern containment of growth rather than its encouragement. As a tribe they tend particularly to enjoy rich, moist soil, but are surprisingly adaptable to poorer, drier conditions.

Where to plant persicaria

Although they do not have the insidious habit of travelling hither and thither by root, the most vigorous clump-formers, such as Persicaria x fennica ‘Johanniswolke’ and Persicaria amplexicaulis, may surprise you with their competitive zeal above ground, and can swamp adjacent plants unless they are similarly competitive. Poorer conditions will restrict their vigour somewhat, as well as splitting and re-planting their clumps regularly in autumn. But the best approach is to let them jostle with other big beasts of prairies, meadows and flower borders, such as Eupatorium maculatum and the aster Doellingeria umbellata, as well as anemones, Vernonia arkansana, Silphium perfoliatum and larger grasses such as Miscanthus sinensis, Molinia caerulea subsp. arundinacea ‘Transparent’ and Panicum virgatum ‘Northwind’, which all have suitable vigour.

Persicaria virginiana (known as jumpseed) and its cultivars may self-seed quite prolifically, but this is quite an innocuous habit as it is easy to remove and indeed, many of its volunteers may be quite welcome. Persicaria runcinata and Persicaria affinis are both much more likely to pose problems and need to be sited with some consideration. Persicaria runcinata travels underground but needs decent light, so being hemmed in by shrubs or paving should be enough to contain its spread. Persicaria affinis is also quite a rapid coloniser, forming a solid interlocking mat of running stems. Its foliage is semi-evergreen so it makes a fairly formidable groundcover plant. This can be a considerable virtue if you are looking to cover a wide area with something attractive that will exclude even the most determined weeds; however, in the mixed border it can become a bit of a nuisance as the wiry stems gain considerable purchase on the soil with their roots, and are hard to extricate from neighbouring plants.

The best Persicaria to grow

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Persicaria amplexicaulis ‘Firedance’

 

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© Dianna Jazwinski

This selection by Dutch designer Piet Oudolf has extraordinarily vibrant colouring. As the flower spikes are slender and accompanied by a proportionate amount of green leaf, as with wildflowers in nature, the colour does not appear too hard. 1.2m. RHS H7, USDA 4a-7b.