Persicaria - Growing Guide

(formerly Polygonum)

Knotweed

Persicarias come in a great range of sizes and overall heights ranging from creeping, rockery or edging species and varieties to much more vigorous clump forming and spreading varieties with very different positioning in the herbaceous border. Some are fully evergreen, some partially so, and some completely deciduous. All are however totally hardy and will grow perfectly well in sun or partial shade providing the soil does not dry out completely.

Propagation is readily achieved by dividing perennial varieties when they go dormant in autumn or in early spring. Creeping varieties can be similarly lifted and divided as they will have rooted themselves as they go.

All Persicarias produce spikes or panicles of flowers on stalkless stems. These are long lasting and some varieties produce a good crop of brown-red seeds.

The other former name for Persicaria is Polygonum which still causes confusion amongst our older customers.

1. Alpine or rockery Persicarias

P. affinis has elliptic lance-shaped dark green leaves and has panicles of bright rose-red flowers fading to pale pink into autumn. It grows to only 8-10in in height with a spread of double this. This is an evergreen.

P. affinis ‘Darjeeling Red’ is a similarly good groundcover plant with flowers which open pink and turn to red when mature.

P. vaccinifolia grows to 6-8in in height with a spread of twice this. The leaves turn an attractive red in autumn and the flower spikes, which also appear in late summer and autumn, are a deep pink. This creeping species is semi-evergreen.

2. Herbaceous border Persicarias

P. bistorta ‘Superbum’ is a vigorous spreading variety which will also naturalise itself in a woodland context if given the chance. It grows to 30in or so in height and can readily spread far wider than this. This is a semi-evergreen perennial with upright spikes of dense soft pink flowers in late summer and well on into autumn. This species will tolerate very dry soil conditions.

P. amplexicaulis ‘Blackfield’ grows a bit taller and is equally vigorous. Its foliage is bronzy and the flowers are a deep red-black but it dies down completely in winter.

P. microcephala ‘Red Dragon’ is another vigorous deciduous perennial with very attractive brownish-red leaves with black markings. It grows to perhaps 3ft or more.