A group of hardy annuals and herbaceous perennials. Most are fully hardy and some are only semi-hardy but all bear sprays or spikes of miniature, bell-shaped, flowers.
This easy to grow, tough and reliable plant is good for mid and late season colour. When massed flower spikes, in shades of pink or white, appear above a dense cover of green leaves. Any mixed border would appreciate one or two varieties of this reliable plant.
Botanical Name: Persicaria
Common Names: Knotweed
Foliage: Deciduous. Green or reddish, simple oval, lance-shaped or elliptic leaves. Many forms turn red or bronze in autumn. A selection of variegated leaf forms are also available.
Flowers: Vertical, long-lasting heads of small red, white or pink flowers, on spikes or panicles.
Flowering Period: Early summer to autumn.
Soil: Any good moisture retentive soil. Chalk, clay, sand or loam. Acid, alkaline or neutral pH.
Conditions: Full sun or partial shade. Any aspect. In an exposed or sheltered position.
Habit: Compact and vigorous, low-growing. Clump/mat forming.
Type: Annuals, herbaceous or evergreen perennials.
Hardiness: Most varieties are fully hardy throughout the UK.
Origin: Native to Europe and West Asia.
Toxicity: Contact with any part of the plant may irritate skin.
Plant in any moisture retentive soil in full sun or partial shade. The best flower and leaf colour is obtained in an open sunny position. Although the low growing forms will tolerate dryish situations, most taller types prefer moist conditions.
Plant from autumn to spring. Divide herbaceous species in early autumn or late winter.
A good choice for mixed borders, cottage gardens, informal gardens or wildflower meadows. Excellent as ground cover. Grow towards the front or middle of the bed. Certain varieties, such as P. bistorta, make good marginal plants.
Cut back flower stems after flowering. Alternatively, flower heads can be left on over winter for effect, then cut back in the spring.
Generally pest and disease free.
Divide mature herbaceous clumps in early autumn or late winter.
Sow the seed under glass in spring and grow-on until large enough to plant out in late summer.
There are many different cultivars of Persicaria available from medium to dwarf height. Flower colours range from red to pink and white
P. affinis (Himalayan bistort) a compact, low-growing variety with pink or red flowers that last from summer through to autumn. Dark green leaves that turn red and bronze in autumn. Height & spread 2ft (60cm).
P. amplexicaulis, dense herbaceous
perennial with small, pale pink or purple flowers on
tall stems from summer through to autumn.
Height: 4ft (1.2m), Spread: 4ft (1.2m).
P. amplexicaulis 'Firedance' (red bistort) a robust, clump-forming perennial with mid-green, wavy-edged, heart-shaped leaves. Salmon-red flowers from midsummer to early autumn. Height to 3ft (90cm).
P. bistorta (snakeweed) vigorous mat forming ground cover. Long lasting pale pink or white flower spikes from early summer onwards. Ideal for pond margins (can be invasive). Height: 2.5ft (75cm), spread: 2ft (60cm).
P. bistorta ‘Superbum’ a fast growing herbaceous form. Clumps or mats of light green oval leaves, above which spikes of pink flowers are produced in early summer. Height up to 3ft (90cm), spread to 2ft (60cm).
P. campanulata (lesser knotweed) compact form with green mat-forming foliage covered by clusters of fragrant pale pink flowers. Native to the Himalayas. Height 3ft (1m), spread 3ft (1m).
Persicaria microcephala 'Red Dragon' a vigorous semi-evergreen perennial with lance-shaped, purplish-green leaves that have a central splash of purple, edged with silver markings. Rounded clusters of tiny white flowers from late summer to autumn. Hardiness H5.
P. milletii clump forming with dense round blooms from mid to late summer. Native to Nepal and China. Height 2ft (60cm), spread 2ft (60cm).
P. mollis tall variety with dense clusters of white flowers. Late summer flowering. Height 8ft (2.4m), spread 2.5ft (75cm).
P. virginiana (jumpseed) tall spikes of creamy white pink-tinged flowers. Bright green, ovate leaves. Native to japan and the Himalayas. Height 4ft (1.2m), spread 2ft (60cm).
P. virginiana ‘Painter’s Palette’ a lovely variegated form with pink and gold spots.