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Persicaria amplexicaulis 'Firetail'
Red knotweed
Himalayas (Pakistan, India, Nepal, Bhutan), southwestern China, central AsiaLearn more
Overview
A vigorous, clump-forming perennial in the family Polygonaceae, a cultivar of Persicaria amplexicaulis native to the Himalayas, China, and central Asia, growing in moist mountain meadows, woodland margins, and stream banks. 'Firetail' forms bold, spreading mounds of large, lance-shaped to ovate, corrugated leaves 4–8 inches (10–20 cm) long on sturdy, branching stems 36–48 inches (90–120 cm) tall. From July through October — one of the longest bloom seasons of any hardy perennial — the plant produces a continuous succession of slender, tapering flower spikes 2–3 inches (5–8 cm) long densely packed with tiny deep crimson-red flowers. The vivid, nearly pure red color of 'Firetail' is among the most saturated reds available in hardy perennials. Plants spread steadily by short rhizomes but are not invasive; the bold foliage and long bloom season make this one of the most reliable and floriferous perennials for the Pacific Northwest, where the cool, moist summers suit it perfectly. Non-toxic.
Native Range
Persicaria amplexicaulis (the parent species) is native to the Himalayas (Pakistan, India, Nepal, Bhutan), southwestern China, and central Asia, growing in moist mountain meadows, open woodland margins, and stream banks at elevations of 6,000–14,000 feet (1,800–4,300 m).Suggested Uses
Planted in mixed perennial borders, woodland edges, and rain gardens at 36–48 inch (90–120 cm) spacing. The deep crimson flower spikes combine dramatically with yellow or orange late-season perennials (rudbeckia, helenium, kniphofia) and ornamental grasses. Effective as a bold specimen in moist, partially shaded positions. One of the most reliable and long-blooming perennials for the Pacific Northwest, particularly in the cool, moist conditions west of the Cascades.How to Identify
Appearance
Size & Dimensions
Height3' - 4'
Width/Spread3' - 4'
Bloom Information
Blooms July through October in zones 4–8 — approximately 16 weeks of continuous flower production, one of the longest bloom seasons among hardy perennials. New flower spikes emerge continuously from the base throughout the season. No deadheading is required to maintain bloom. Peak flower production is in August and September; the display continues until hard frost. In the Pacific Northwest, bloom persists reliably until mid-October.Detailed Descriptions
Flower Description
deep crimson-red; slender, tapering bottlebrush spikesFoliage Description
medium to dark green, lance-shaped to ovate, large, corrugated, stem-claspingGrowing Conditions
Sun Requirements
Requires 3-6 hours of direct sunlight daily
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Care & Maintenance
Care Guide
Plant in full sun to partial shade in consistently moist, fertile, humus-rich soil with a pH of 5.5–7.0. Requires consistent moisture — performance declines significantly in dry conditions. Tolerates clay soils and occasional waterlogging. Best performance in cool, moist Pacific Northwest summers where it blooms for 4 months. Space at 36–48 inches (90–120 cm) — plants spread steadily by short rhizomes. Divide every 3–4 years in early spring to control spread and maintain vigor. No staking required; stems are sturdy.Pruning
Cut all stems to ground level in fall after frost or in late winter before new growth emerges. No deadheading needed during the growing season — spent spikes can be removed for tidiness, but new spikes emerge continuously without intervention. Divide every 3–4 years in early spring by lifting the clump and separating rhizome sections; replant vigorous outer portions at 36 inch (90 cm) spacing.Pruning Schedule
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fallearly spring