How to Grow Purple Knight Alternanthera
Purple Knight Alternanthera
Alternanthera dentata 'Purple Knight'
shrubPurple Knight is a striking ornamental foliage plant prized for its deep burgundy to purple leaves that intensify in color under bright light. This compact, bushy cultivar grows 12-18 inches tall and is commonly used in containers, borders, and as a tender annual in temperate climates. The plant produces small, insignificant white or pale flowers, but is grown primarily for its stunning year-round foliage.
When should you plant Purple Knight Alternanthera in your zone?
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Example Purple Knight Alternanthera timeline · Pittsburgh, PA (Zone 6b)
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Plant Purple Knight Alternanthera
Around Apr 17Near Pittsburgh's average last spring frost.
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Tend & protect
Late spring–summerWatering, feeding, and pest-watch reminders.
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Harvest Purple Knight Alternanthera
Around May 17≈ 30 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Purple Knight Alternanthera dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 10b-11; grown as an annual or container plant in cooler zones
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Seedling
2-3 weeksTiny green seedlings emerge with opposing oval leaves. Plants are delicate and grow slowly.
Maintain consistently moist (not soggy) soil. Provide bright, indirect light. Keep in warm environment (70-75°F). Thin or transplant when 2-3 true leaves appear.
Vegetative Growth
4-6 weeksPlant develops multiple stems and bushy form. Leaves are initially green or light purple, gradually deepening in color with increased light exposure.
Pinch growing tips regularly to encourage bushiness. Gradually acclimate to brighter light and outdoor conditions if growing indoors. Feed with balanced fertilizer every 2-3 weeks.
Mature Foliage
Ongoing during growing seasonPlant reaches full compact, mounding form with dense, rich purple foliage. Color deepens to deep burgundy under full sun.
Maintain regular watering and feeding schedule. Continue pinching to maintain shape. Increase sun exposure to intensify color. Monitor for pests.
Flowering
Spring to fallSmall white or pale pink flowers appear in terminal spikes among the foliage, though they are inconspicuous.
Deadheading is optional since flowers are not showy. Plant is grown for foliage rather than flowers.
Dormancy/Winter
November-FebruaryIn zones 10-11, growth slows but plant remains evergreen. In cooler zones grown as annual, plant dies back after frost.
Reduce watering in dormant period. Move container plants indoors if frost threatens. In warm climates, may prune back to 6 inches in late winter to rejuvenate.
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Spray with insecticidal soap or neem oil; encourage air circulation to reduce humidity
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Increase humidity by misting; spray with water to dislodge; use neem oil if severe
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Remove with cotton swab dipped in rubbing alcohol; spray with neem oil or insecticidal soap
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Spray with water to remove; use insecticidal soap or horticultural oil if infestation is severe
Uses
Traditional medicinal leaf tea
CulinaryIn some tropical regions, Alternanthera dentata leaves are brewed as a traditional herbal tea believed to have diuretic and health-promoting properties. The leaves have a mild, slightly bitter flavor. [source]
Ornamental container and landscape design
HouseholdPurple Knight is widely used in container gardens, hanging baskets, borders, and bedding displays for its striking burgundy foliage that adds color and texture. It serves as an excellent focal point or accent plant in mixed plantings. [source]
Indoor houseplant
HouseholdWhen grown indoors near a bright window or under grow lights, Purple Knight makes an attractive compact houseplant that adds color to interior spaces. It tolerates typical indoor temperatures and humidity. [source]
Butterfly garden nectar plant
WildlifeAlthough small and inconspicuous, the flowers attract butterflies and other small pollinators, making Purple Knight a useful addition to wildlife-friendly gardens. [source]
Harvest Tips
This is an ornamental foliage plant not typically harvested. However, stem cuttings can be taken year-round for propagation in water or moist soil. Pinch off growing tips and stems regularly to maintain compact, bushy form and remove any leggy growth.
Fun Facts
- 🌱 Purple Knight's intense burgundy color is enhanced by high light levels; plants grown in shade will be predominantly green, demonstrating how light intensity directly affects pigment production.
- 🌱 The plant is sometimes called 'Joseph's Coat' due to its multi-colored foliage in some conditions, though Purple Knight is specifically bred for deep purple coloration.
- 🌱 Alternanthera dentata is native to South America and is part of the amaranth family, making it a relative of both ornamental celosia and edible amaranth.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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