How to Grow Alligatorweed
iNaturalist
Alligatorweed
Alternanthera philoxeroides
herbAlligatorweed is a semi-aquatic perennial plant with small oval leaves and insignificant white flowers, native to South America. It thrives in wet environments, ditches, marshes, and along waterways, and is considered highly invasive in many regions outside its native range. The plant spreads rapidly via fragmentation and creeping stolons, making it a significant ecological pest in North America, Europe, and Australia.
When should you plant Alligatorweed in your zone?
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Example Alligatorweed timeline · Pittsburgh, PA (Zone 6b)
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Plant Alligatorweed
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 Alligatorweed
Around Apr 21≈ 4 days after planting
Sample dates for Pittsburgh, PA. Sign up to get exact Alligatorweed dates for your own zip code.
Growing Conditions
Soil
Growing Zones
Find your zone →Thrives in zones 8-11; frost-sensitive but spreads vigorously in warm, wet climates
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Establishment
2-4 weeksFragmented stems or cuttings develop roots and establish in wet soil or water within 2-4 weeks
Keep cuttings in consistently wet conditions; propagation is highly successful even from small fragments
Vegetative Spread
Ongoing throughout growing seasonPlant develops creeping stolons and new rooting nodes, expanding laterally across wet substrate
Growth is vigorous and difficult to control once established; spreads both horizontally and vertically
Stem Elongation
6-12 weeksStems grow 4-12 inches tall with opposite, oval leaves in a compact arrangement
Regular trimming can slow spread but does not eliminate the plant; remove before flowering to prevent seed production
Flowering
Episodic throughout warm monthsProduces small, inconspicuous white flowers in leaf axils; flowering is sporadic and sparse
Remove flower buds if possible to prevent seed development; seeds are viable but less important than vegetative spread
Dormancy
Winter months (zones 8-9)Growth slows or stops in frost-prone zones; foliage may die back or discolor below 50°F
Surviving root systems can regrow from any fragment in spring; do not compost or discard fragments near water
Companion Planting
Plan your garden →Plant with:
Avoid planting near:
Common Pests
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Natural pest in native range; rarely controlled in cultivated settings as plant is not typically grown intentionally
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Remove affected leaves; improve air circulation; not a significant concern
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Occurs in stagnant water; improve water quality; remove severely rotted stems
Uses
Traditional herbal medicine
MedicinalUsed in traditional Chinese and Ayurvedic medicine for anti-inflammatory and diuretic properties. Some evidence suggests compounds may have antimicrobial and antioxidant activity. [source]
Aquatic animal habitat (native range)
WildlifeIn South America, the plant provides shelter and food sources for aquatic insects, fish, and waterfowl. However, it degrades native ecosystems in invaded regions. [source]
Biological control agent research
HouseholdThe plant is studied as a target for biological control in invaded regions. Herbivorous insects from the native range are being investigated as potential control agents. [source]
Vegetable in Southeast Asian cuisine (limited use)
CulinaryIn some parts of Southeast Asia, tender shoots are eaten as a vegetable in soups and stir-fries, though it is not widely cultivated for this purpose. [source]
Invasive species management research
EcologicalExtensively studied as a model for understanding and managing aquatic plant invasions; research focuses on control methods, ecological impacts, and prevention strategies. [source]
This is not medical advice. LizPlants is not a medical resource. Always consult a qualified healthcare professional before using plants medicinally.
Harvest Tips
Do NOT harvest for propagation in non-native regions; the plant is invasive and any harvested material (even small fragments) can establish new populations. In regions where control is necessary, remove all visible stems and roots before frost, bag material in sealed containers, and dispose of in trash or burn. Never compost or discard near waterways.
Fun Facts
- 🌱 Alligatorweed is native only to South America but has become one of the world's most problematic aquatic invasive species, spreading to North America, Europe, Asia, and Australia since the 1890s.
- 🌱 The plant reproduces with extraordinary efficiency: a single fragment as small as 5-10 mm can regenerate into a complete plant, making control efforts extremely difficult.
- 🌱 In Australia, the plant has been deliberately introduced as a biological control agent—ironically, it itself became such a severe invasive pest that millions of dollars have been spent trying to eradicate it.
Gardening Terms
New to gardening? Learn about terms used in this guide:
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