Knotweed (Persicaria microcephala 'Red Dragon')
Discover Persicaria microcephala 'Red Dragon' (Knotweed), a low-maintenance perennial prized for striking purple-tinged foliage and summer white flowers.
Complete Plant Information
Overview
Persicaria microcephala ‘Red Dragon’, commonly known as Knotweed, offers dramatic visual impact with foliage that changes color throughout the season. This herbaceous perennial is especially valued for its unique leaf coloration, distinguishing it significantly from its spreading relatives. Gardeners appreciate this cultivar for providing reliable, eye-catching texture in partially shaded borders.
Unlike the stoloniferous species plants, the cultivar ‘Red Dragon’ maintains a desirable clump-forming habit, offering structure without overwhelming garden space. It reaches a modest height of 2 to 2.5 feet, making it an excellent mid-border component. The mild flowers appear in mid to late summer, complementing the evolving leaf tones.
This Knotweed variety provides excellent visual interest from spring emergence through fall dormancy, demanding minimal effort for maximum reward. Its low maintenance level and adaptability to various light conditions establish Persicaria microcephala ‘Red Dragon’ as a flexible and rewarding choice for cottage or woodland-style gardens seeking consistent color contrast.
Fast Facts
- Plant Family: Polygonaceae
- Plant Type: Herbaceous perennial
- Hardiness Zones: USDA Zones 6-8
- Size at Maturity:
- Height: 2-2.5 ft
- Spread: 2.5-3 ft
- Bloom Time: July to August
- Bloom Description: White
- Sun Exposure: Full sun to part shade
- Water Needs: Medium
- Maintenance Level: Low
How to Grow
For the best performance, establish your Persicaria microcephala ‘Red Dragon’ in the spring or early fall when temperatures are mildest. This Knotweed variety thrives best in moist, moderately fertile, well-drained soils. While it tolerates full sun, partial shade helps protect the vibrant leaf color, ideally receiving protection from intense afternoon heat.
Maintain soil moisture consistency throughout the growing season; these plants thrive when kept evenly moist but not waterlogged. Due to its moderate water needs, supplemental irrigation during dry spells is often necessary, especially in hotter climates. Fertilization requirements are generally low; rich soil is often sufficient, and heavy feeding can sometimes encourage excess, less vibrant foliage growth.
Pruning is generally minimal for this clump-forming cultivar. Deadheading spent flower spikes is optional but can tidy the appearance post-bloom in late summer. As a sterile cultivar, unlike the standard Knotweed, you do not need to worry about aggressive runners; simply trim back the foliage in early spring before new growth emerges to clean up the area.
Landscape Uses
The distinctive foliage of Persicaria microcephala ‘Red Dragon’ makes it a fantastic anchor plant in mixed containers, providing deep, complex color that contrasts well with lighter green or variegated companions. It is highly recommended for mass plantings in woodland or cottage gardens where a rich tapestry of texture is desired.
Use this Knotweed variety strategically in borders to provide mid-level structure. Its reddish stems and developing purple-brown leaves offer early-season intrigue before the summer flowers appear. Because deer and rabbits generally ignore this plant, it can be safely placed near edible garden edges where other perennials might be browsed.
Consider pairing this variety with plants that appreciate similar moist, partial-shade conditions, such as Hosta, Tiarella (Foamflower), or Astilbe. The white blooms of the Knotweed in July and August harmonize beautifully with pink or blue shade-loving flowers.
Standout Features
Flower Qualities
- Showy
- Good Cut
Noteworthy Characteristics
Persicaria microcephala, commonly known as knotweed or fleeceflower, is an herbaceous perennial that typically grows to 24” tall. It is native to forests and grassy areas in China. It is a stoloniferous spreader that is noted for having green stems clad with broad-ovate to triangular-ovate green leaves (to 2-4” long), each leaf being decorated with a lighter green chevron. Leaves remain green throughout the growing season. Campanulate white flowers (each to 1 1/4” long) bloom in late summer. Polygonum microcephalum is a synonym.Genus name comes from the Latin persica meaning peach-like and sagittata meaning barbed or arrow-shaped in reference to the shape of the leaves.Specific epithet comes from Greek meaning small-headed in reference to flower size.‘Red Dragon’ is a cultivar that typically grows to 30” tall and to 36” wide. In comparison to species’ plants, it is distinguished by having (a) red stems, (b) leaves which emerge purple-brown with a gray-brown to mint green chevron in spring, with the leaves turning silver-purple and finally green with maturity, and (c) a clump-forming rather than stoloniferous habit. ‘Red Dragon’ was discovered as a naturally occurring mutant seedling that appeared in a crop of Persicaria microcephela being grown for medicinal purposes in Nanjing, China. Pollen and seed parents are Persicaria microcephala. First asexual reproduction of ‘Red Dragon’ occurred in April of 1997 when the inventor, C. Greg Speichert, took cuttings of this new plant in St. John, Indiana. Flowers bloom July-August. U.S. Plant Patent PP12,062 was issued on August 21, 2001
Tolerances
- Rabbit
- Deer
Potential Problems
Fortunately, Persicaria microcephala ‘Red Dragon’ rarely faces significant challenges from pests or diseases under appropriate conditions. Gardeners should monitor for signs of fungal issues if the plant receives poor air circulation or stays perpetually soggy, though this is uncommon for the species. Proactive cultural care—ensuring well-drained soil and adequate airflow—is the best defense against any potential problems.
Frequently Asked Questions
What hardiness zones is Knotweed (Persicaria microcephala ‘Red Dragon’) suitable for?
This specific Knotweed cultivar is hardy in USDA Zones 6 through 8, requiring protection or consideration for overwintering if planted outside this range.
How large does Knotweed (Persicaria microcephala ‘Red Dragon’) grow?
Mature specimens of Persicaria microcephala ‘Red Dragon’ typically reach a height between 2 and 2.5 feet, spreading to a width of 2.5 to 3 feet.
When does Knotweed (Persicaria microcephala ‘Red Dragon’) bloom?
Persicaria microcephala ‘Red Dragon’ produces its attractive white flowers during the peak summer months, specifically blooming from July through August.
What sun exposure does Knotweed (Persicaria microcephala ‘Red Dragon’) need?
This plant performs well in locations receiving full sun to part shade, though some afternoon shade may help preserve the richest leaf coloration.
Conclusion
The unique, evolving foliage color and manageable, clump-forming nature make Persicaria microcephala ‘Red Dragon’ a standout perennial for textured, low-maintenance gardens. If you seek dark, contrasting foliage punctuated by delicate white flowers, this Knotweed is an excellent choice. Always confirm your local hardiness zone compatibility before planting this superb ornamental.
Companion Planting
Choosing thoughtful partners enhances the appeal of Persicaria microcephala ‘Red Dragon’. Look for varieties that thrive in medium moisture and partial shade, which complements the Knotweed’s cultural preferences. Low-growing, bright green groundcovers, such as creeping Jenny (Lysimachia nummularia ‘Aurea’) or Japanese Forest Grass (Hakonechloa macra), create a luminous base beneath the darker leaves of the Knotweed.
For taller accents in a woodland garden setting, consider pairing this perennial with ferns that appreciate moisture or deep purple foliage plants like certain Heuchera cultivars. The subtle white blooms of this Knotweed provide a cool contrast against warmer-toned flowers like pink Astilbe or coral Heuchera blooming simultaneously in mid-summer.
Seasonal Care Calendar
Early spring cleanup involves removing any remaining winter debris and cutting back old stems of the Persicaria microcephala ‘Red Dragon’ just as new growth begins to emerge from the crown. This timing keeps the plant tidy and encourages fresh, vibrantly colored stems and leaves.
Summer care centers primarily on irrigation; ensure your Knotweed receives consistent medium watering, especially during dry heat waves, as soil moisture directly impacts foliage quality. Deadheading spent white flower clusters is optional but recommended if you are using the plant as a cut flower or prefer a neater border appearance into the late season.
As fall approaches, minimal intervention is needed, as this herbaceous perennial naturally dies back. Simply allow the foliage to wither naturally unless you wish to tidy the area before winter. In colder regions near the zone 6 edge, a light layer of mulch applied after the ground freezes can offer extra insulation for the root zone of your Persicaria microcephala ‘Red Dragon’.
