White top, Congress weed
parthenium hysterophorus
Also known as: ["Carrot weed","Bitter weed","Santa Maria feverfew"]
Overview
An invasive annual herb native to the Americas, known for its rapid spread and allergenic properties.
Benefits & Perks
["fast growing","wildlife attractant (bees, butterflies, birds)","drought tolerant"]
Botanical Classification
| Phylum: | Magnoliophyta |
| Class: | Magnoliopsida |
| Order: | Asterales |
| Family: | Asteraceae |
| Genus: | Parthenium |
| Botanical Name: | Parthenium hysterophorus |
Plant Characteristics
Basic Information
- Category: Herbs & Weeds
- Suitable Location: outdoor garden bed or container in warm climates
- Suitable For:
- Is Weed: No
- Allergenicity: high
Environmental Needs
- Climate: {"temperatureRange":"10–35°C"}
- Hardiness: {"zones":"8–11"}
- Misting: rarely required
- Drainage: Fast-draining to prevent waterlogging.
- Soil Type: Well-draining, sandy loam with organic matter; avoid heavy clay.
Maintenance Level
- Maintenance Level: very low
- Toughness Level: very high
- Pruning Frequency: As needed; lightly prune throughout growing season; major pruning after flowering.
- Pruning Intensity: Moderate; remove up to one-third of growth if overgrown.
Care Details
Ideal Sunlight Coverage:
Full sun (6–8 hours/day); tolerates partial shade but may become leggy.
Sunlight Tolerance Tips:
Acclimate gradually if moving from shade to sun; protect from intense midday sun in hot climates; ensure good air circulation to prevent fungal issues.
Care Requirements
Care Difficulty
expert onlymoderate
Sunlight
full sun to partial shade
Rotate plant for even growth; use sheer curtains in intense sun; avoid direct afternoon sun in summer.
Watering
every 7–10 days during active growth, less frequently in dormant periods
Water thoroughly but infrequently; ensure good drainage; avoid wetting foliage.
Soil
well-draining, sandy or loamy soil
pH: Slightly acidic to neutral (pH 6.0–7.0).
Use raised beds for better drainage; avoid compacted soil; mulch to retain moisture.
Temperature
Warm conditions (65–85°F/18–29°C); sensitive to frost.
Avoid sudden temperature changes; protect from drafts; maintain consistent warmth.
Fertilizing
rarely required, if used then every 3 months with balanced fertilizer
Fertilize only when actively growing; flush soil occasionally to prevent salt buildup; use organic options for gentle feeding.
Propagation
Methods
Stem cuttings or seeds; stem cuttings are faster and more reliable.
Step-by-Step Propagation Guide
- Take 4–6 inch cuttings.
- Remove lower leaves.
- Dip in hormone.
- Plant in medium.
- Keep moist and warm.
Best Time: Spring or early summer when growth is active.
Environment
Warm (70–75°F/21–24°C), high humidity, and bright indirect light.
Medium
Well-draining mix like perlite and peat moss or cactus mix.
Hormone
Rooting hormone is optional but recommended for faster rooting.
Timeline
Roots develop in 2–4 weeks; establish in new pot within 6–8 weeks.
Tools Needed
Pruners, rooting hormone, small pots, well-draining medium.
Quick Tips
Use healthy, non-flowering stems; maintain humidity with a plastic cover; avoid overwatering.
Pruning & Repotting
Pruning Guide
Method
Pinch back tips for bushiness; cut just above a leaf node or bud.
Pruning Plan
Remove dead or leggy growth to encourage bushier form; prune after flowering to promote rebloom.
Tools
Clean pruners or scissors, disinfectant.
Checklist
Sanitize tools; prune dead/damaged growth; shape plant; clean up debris.
Repotting Guide
Best Season
Spring, before active growth begins.
Pot Size
One size larger pot (e.g., +2 inches in diameter).
Method
Remove plant gently; trim roots if needed; place in new pot with fresh soil; water lightly.
Suggestions
Repot every 1–2 years or when roots fill the pot; beneficial for growth and health.
Checklist
Choose appropriate pot; prepare new soil; handle roots carefully; water after repotting.
Advanced Care Tips
Watering Mastery
Watering Checklist
Check soil moisture; water deeply; ensure drainage; avoid wetting leaves.
How to Apply Water Properly
Water directly at the root zone until water drains from the bottom; allow excess to drain away; water early in the day to minimize evaporation.
Watering Schedule Tips
Water deeply once the top inch of soil is dry; reduce frequency in winter to prevent root rot.
Soil Improvement
Add perlite or sand for drainage; incorporate compost for fertility; ensure aeration with organic matter.
Temperature Stress Management
Signs of Temperature Issues
Wilting, yellowing leaves, stunted growth, or bud drop in extreme heat or cold.
Cold Stress
Growth slows or halts; leaves may turn yellow or brown; risk of frost damage.
Solution: Move to a warmer location; provide frost protection if outdoors; avoid overwatering in cold conditions.
Hot Stress
Leaf scorch, wilting, or drooping; reduced flowering; potential for heat stress.
Solution: Provide shade during peak heat; increase humidity; water early in the day.
Fertilizing Guide
Fertilizing Checklist
Check growth phase; dilute fertilizer; apply to soil; avoid foliage contact.
Fertilizing Method
Use balanced liquid fertilizer diluted to half strength every 4–6 weeks during growing season; avoid fertilizing in winter.
Common Problems & Solutions
Toxicity Warning
Cats
ToxicCats are susceptible to toxicity from Parthenium hysterophorus upon ingestion. The plant can cause severe gastrointestinal irritation and allergic responses.
⚠️ Symptoms:
🌿 Toxic Parts:
⚡ Toxic If:
if eaten
Dogs
ToxicIngestion of Parthenium hysterophorus by dogs can cause significant gastrointestinal upset and allergic reactions. The plant contains compounds that are irritating to the digestive tract.
⚠️ Symptoms:
🌿 Toxic Parts:
⚡ Toxic If:
if eaten
Humans
ToxicParthenium hysterophorus is known to cause severe allergic reactions and dermatitis upon contact. Ingestion can lead to gastrointestinal distress and systemic toxicity due to its irritant compounds.
⚠️ Symptoms:
🌿 Toxic Parts:
⚡ Toxic If:
if eaten or touched
Frequently Asked Questions
Q: Is Parthenium hysterophorus toxic to humans?
A: Yes, it is toxic and can cause dermatitis and respiratory issues upon contact or inhalation.
Q: How does this plant spread?
A: It spreads rapidly through wind-dispersed seeds and vegetative growth, making it highly invasive.
Q: Can this plant be controlled?
A: Control is challenging due to its high resilience; mechanical removal and herbicides are often required.
Quick Reference
| Family: | Asteraceae |
| Care: | expert only |
| Light: | full sun to partial shade |
| Water: | every 7–10 days during activ |
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